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Asian Journal of Plant Pathology

The possible carryover effect of three fungicides and one insecticide on results
of PCR and Multiplex-PCR for detection of bacterial pathogens was studied. The
potato brown rot caused by phylotype II, sequevar I of Ralstonia solanacearum
and the potato ring rot bacteria Clavibacter michiganensis ssp. sepedonicus
were considered in this study. Under optimized conditions for PCR activity,
the potato extract prepared from the Cara potato cultivar did not interfere
with band development of DNA’s
extracted from the organisms in concern. Regardless of their mode(s) of action,
the studied pesticides exerted different effect(s) on band development according
to their chemical grouping. The dimethomorph (Acrobat), systemic fungicide,
caused complete inhibition of band development of DNA extracted from either
potato brown rot or potato ring rot bacteria which may be considered as false
negative reaction(s). The propamocarb carbamate (Previcur N), systemic fungicide,
did not inhibit band development of the organisms in concern. The dithiocarbamate
plus zinc and manganese (Diathane M45), contact fungicide however, caused a
complete band inhibition of ring rot DNA contrary to that being reported for
brown rot, indicating a preferential polymerase activity. The organophosphate
(Malathion), penetrative non-systemic insecticide, did not inhibit DNA band
development for both organisms. Multiplex-PCR of mixed DNA’s
of R. solanacearum and C. michiganensis ssp. sepedonicus
caused a false negative reaction through inhibition of band development of R.
solanacearum but not for C. michiganensis ssp. sepedonicus,
under the effect of propamocarb carbamate (Previcur N) fungicide and organophosphate
(Malathion) insecticide. It could be concluded that the pesticides carryover
effect on PCR results of potato brown rot and ring rot bacteria are being variable
according to the pesticide grouping. The dimethomorph (Acrobat) fungicide caused
false negative effect with both organisms under study followed by dithiocarbamate
(Diathane) fungicide in case of ring rot bacteria. The false negative multiplex-PCR
is being evident only in case of R. solanacearum under the stress of
both propamocarb carbamate (Previcur N) fungicide and on the organophosphate
(Malthion) insecticide. The mode of action of the used pesticide, either contact
or systemic, had no effect on PCR or multiplex-PCR results. Further investigations
are needed with different groups of pesticide. 2014/03/29 - 11:21

Study for the genetic diversity of P. oryzae populations, under natural
inoculation, trapping of virulence races present in ecosystems, was done during
the period of 2008 to 2010 in two countries. One location/country was surveyed
to highlight that resistance genes: Pi1; Pi11; Pi12; Pi19; Pib; Pi20; Pi5; Pi7;
Pia; Pia+Pi19; Pia+Pish; Pif, Pii, Pik, Pik-p, Pish, Pit, Pit, Pita-2, Piz,
Piz-t, Piks at M'be and and those at Ouedeme: Pi1, Pi12, Pi19, Pi1b, Pi3, Pi5,
Pi7, Pia, Pii, Pik, Pi-p, Pit, Pita, Piks incidence. It was shown that they
were overcome by a large proportion of the virulence gene of P. oryzae
population. However, virulence genes that are capable of overcoming resistance
genes: Pi33, Pi5 (t), Pi7, Pi9, Pikh+Pi-1+Pita+Pita, Pik-m ,Pish, Pitta-2, Piz-5,
were absent or rare. These genes were effective against the pathogen population
studied. This study also showed that Pi5 and Pi7, Pikh +Pi-1+Pita+Pita, genes
association which were individually inefficient, has conferred a sustainable
resistance to blast that was observed in Moroberekan and Tetep. This work will
help rice breeders and plant pathologists to select rice varieties with durable
resistance to blast disease. 2014/03/29 - 11:21

In the present study, the pathogenic fusaria viz., Fusarium solani f. sp. melongena and F. oxysporum f. sp. lycopersici causing brinjal and tomato wilt were isolated from soil as well as from the infected plant parts. In vitro efficacy of three medicinal plants viz., Azadirachta indica (leaf extract), Psidium guajava (leaf extract), Eucalyptus camaldulensis (bark extract) and three fungal antagonists viz., Trichoderma harzianum, T. atroviride and T. longibrachiatum were tested at 25, 50 and 75% (v/v) by poisoned food technique against both the pathogens. The assessment of fungitoxicity was carried out in terms of percent mycelial growth inhibition against the test fungi. Among different medicinal plant extracts, Azadirachta indica (leaf) was found significantly superior to the rest in suppressing the growth of F. oxysporum f. sp. lycopersici as 100% inhibition was recorded at 50 and 75% concentration followed by Psidium guajava and Eucalyptus camaldulensis on 7th day of inoculation. On the other hand, among different microbial antagonists, T. longibrachiatum against both the test fungi was highly effective and there was 100% inhibition of mycelial growth at 50 and 75% concentration, while T. harzianum was effective against F. oxysporum f. sp. lycopersici followed by T. atroviride as it completely inhibited the mycelial growth at 75% concentration. 2014/03/29 - 11:21

Four dominant fungi viz., Alternaria alternata, Aspergillus niger,
Penicillium rubrum and Fusarium moniliformae were selected after
isolation from mungbean seeds genotype HUM-12 and HUM-4. The seeds were infested
with above dominant fungi. Moisture content of (fresh and infested both) were
determined during different period of storage. Moisture content of mungbean
seed was decreased due to infestation of selected dominant seed mycoflora. The
results showed that Aspergillus niger infested mungbean seeds showed
minimum moisture content followed by Penicillium rubrum. Highest Moisture
content was recorded in freshly harvested mungbean seed genotype HUM-12 followed
by HUM-4. 2014/03/29 - 11:21

Among diseases affecting rice production, blast, sheath and bacterial leaf blight causes significant losses. This study was aimed to control multiple rice diseases using beneficial bacterial consortium as an alternative biocontrol strategies. In vitro, greenhouses and field test were carried out to study antagonistic effect of bacterial consortium against rice pathogens. The bacterial isolates used in single or in mixture combination were apparent to reduce sheath blight, neck blast and bacterial leaf blight under in vitro test. The suspension formulation mixture of A6 (B. firmus E 65, P. aeruginosa C32b, B. cereus II 14), A8 (B. firmus E65, Serratia marcescens E31, P. aeruginosa C32b, B. cereus II 14), talc based-A8 and animal compost granule-A8 had percentage inhibition to P. oryzae of 71.04, 79.19, 63.87 and 66.68%, respectively. P. aeruginosa C32a produced glucanolytic index of 2.26 and specific activity of 0.448 U mg-1. In greenhouse test, the lowest intensity of neck blast was shown by A6 treatment. Bentonite formulation showed good effect in suppressing bacterial leaf blight lesion length in greenhouse test. The cell viability decrease was ranged from 2.39 to 18.30% among different bioformulations. Talc-A8 based formulation was stable at period of storage showing no viability lost. Talc-A5 (Bacillus firmus E65, Pseudomonas aeruginosa C32b) formulation was effective against sheath and bacterial leaf blight but showed lower effect on neck blast disease in the field. Further studies should focus on the evaluation of different carriers other than talc-based powder as stable and cheaper media, then scale-up possibilities for further applications. 2013/10/24 - 19:48

This study was designed to evaluate the antagonistic effects of rhizobacterial
antagonists against Coffee Wilt Disease (CWD) caused by Gibberella xylarioides
under in vitro and in vivo conditions. Arabica coffee is Ethiopia’s
main export crop. However, the production and productivity of coffee is being
challenged primarily by coffee vascular disease (tracheomycosis).The greenhouse
antagonism study was conducted with four antagonistic bacteria of one Bacillus
(JU544) and three Pseudomonas spp. (JU941, JU13 and JU23). Out of 81
rhizobacterial antagonists tested on Half Strength King’s B (HSKB) medium
against G. xylarioides, 13.6% of them significantly (p<0.0001) reduced
the radial mycelial growth of the pathogen. From 11 rhizobacterial isolates
tested for their phytobeneficial traits, eight of them produced protease. Nevertheless,
five of them produced Hydrogen Cyanide (HCN) and other lytic enzymes. The bio-control
agents, time of applications and the interaction of the two were significantly
(p<0.0001) reduced the CWD severity and incidence under greenhouse conditions.
The CWD control efficiency was significant (p<0.0001) and the highest bio-control
efficiency was 72.64% when the coffee seedlings were treated with Bacillus
spp. (JU544) seven days before the pathogen. The bacterial antagonists, time
of applications and interaction of the two significantly (p<0.001) reduced
the progression of CWD incidence. The rhizobacterial antagonists especially
Bacillus spp. (JU544) effectively reduced CWD severity and incidence
under greenhouse condition and can be further evaluated under field condition
to ascertain their future applicability for inoculum development. 2013/10/24 - 19:48

The present study was to investigate the variation among Glomus species.
Standard method used for Extraction, purification of Vesicular Arbuscular Mycorrhizal
(VAM) fungi, during summer and winter season. Study Effect of some factors on
number of spores collected from the rhizosphere of various plants in Egypt.
Used single spores technique inoculated on maize root to purified and identified
isolates of Glomus spp. The highest number of spores was found in summer
season while the lowest number was found in winter season. Variation of Glomus
spp. isolates among polymorphic DNA markers was studied. Species 2, 3, 4
and 7 identified by VANS1/VALETC primer as Glomus etunicatum. Fatty Acid
Methyl Ester (FAME) profiles were analyzed to assess the diversity and quantity
of fatty acids in 8 isolates of Glomus species. Spores and endomycorrhizal
roots of Sudan grass (Sorghum sudanense) were examined. Analysis of lipid
for species found that affinity specific and generic levels. Differentiation
on the genus level using lipid profiles and content which was carried out by
evaluating the methyl esters of fatty acids, revealed convergence between studied
isolates. Palmitic acid (16:0), Oleic acid (cis18:1n9) and Stearic acid (18:0)
were the dominant fatty acid of the Glomus spp., while the dominant fatty
acids of Glomus etunicatum isolates were myristic acid (14:0) palmitoleic
acid (16:1n7 cis), archidic acid (20:0), palmitic acid (16:0), oleic
acid (cis18:1n9) and stearic acid (18:0). This study indicates that using lipids
as biochemical markers to identify the different genus of AM fungi and differentiate
between the species. 2013/06/30 - 03:41

The study was conducted to estimate yield and quality losses attributed to potato seed tuber cycle and latent infection at Shashemene Ethiopia. Four consecutive seasons (2009B to 2011A) at five ‘kebeles’ using three improved potato varieties of Jalene, Gudenie and Awash and two local varieties, ‘Nech abeba’ and ‘Agazer’ was done using previous harvest seed for the following season. The results indicated that seed tuber cycle significantly (p<0.05) affected the progress of the disease on the local varieties as compared to improved varieties. The incidence of the disease in the field and the incidence of latent infection in tubers was highly significant (p<0.001) between varieties and among progeny tubers produced in different seasons. In the inception of the trial year, in the field, in the first cycle, the local variety had significantly (p<0.05) higher (20.93%) BW incidence than the improved varieties (3.98%), whereas in the 4th cycle the disease incidence increased to 26 and 53%, respectively. In the 4th cycle of progeny tubers, the incidence increased by 75 and 50% from the 1st cycle, respectively. Under ware potato production, in the first cycle, the yield loss was 4 and 7% in improved and local varieties whereas, in the 4th cycle, it increased to 21 and 32%, respectively. When potato was produced for seed, in the first cycle, the loss was 5.34 and 20.78% on improved and local varieties but in the 4th cycle it increased to 28.6 and 67.34%, respectively. Therefore, the study revealed that source of seed and year after year seed revolving were found to be the major factor and the main path for the dissemination of BW disease. 2013/06/30 - 03:41

Microbial contamination of vegetables, especially leafy ones, is a common problem
during growth under field conditions and their consumption without washing can
create human health hazards. Therefore, the main objective of this study was
to assess the microbial quality and determine suitable treatments of lettuce
produced in Hofuf, Saudi Arabia. A total of 150 lettuce samples were collected
for the study. The samples were treated with vinegar (5% acetic acid) and with
disinfection tablets containing sodium dichloroisocyanurate for microbial infection
treatment. The contamination of different microbes was determined under different
growth media and temperatures. Mean counts of mesophilic aerobic bacteria were
5.06-6.70, 3.38-4.80 and log 4.97-5.99 CFU g-1 in outer leaves, inner
leaves and composite samples of whole head leaves, respectively. Mean counts
of coliforms, yeasts and molds didn’t reach log 3 CFU g-1. The
counts of mesophilic aerobic bacteria seem to increase during handling, counts
of coliforms and yeasts remain constant while those of molds decrease. The E.
coli 1 was detected in 5 out of 45 samples tested for this bacterium while
no Salmonella or S. aureus were detected in these samples. Soaking
in vinegar was effective against mesophilic aerobic bacteria, coliforms and
yeasts at concentrations 25-100% and reduced contamination by up to 3 log cycles
but it was less effective against molds. In conclusion, treatments such as washing
with tap water and vinegar (5% acetic acid) reduced the microbial contamination
level significantly for safe human consumption. 2013/06/30 - 03:41

Pepper yellow leaf curl disease which is caused by Pepper Yellow Leaf Curl Virus (PepYLCV) is one of the major problems in chili pepper (Capsicum annuum) cultivation in Indonesia. Reducing of the yield could reach 100% in some condition. For this reason, well understanding of virus distribution as well as their genome structure is very crucial for combating the disease. Based on this rationality we characterized genome structure of PepYLCV isolate designated as PepYLCWSV-TD21 which was collected from chili cultivation pepper population in West Sumatera. The result indicated that the PepYLCWSV-TD21 had a monopartite genome and dominantly infected compared to its bipartite counterpart. This was confirmed by analysis of DNA-β presence by specific primer pair Beta01/Beta02. Annotation of both genome structure successfully identified 6 open reading frames designated as V1, V2, C1, C2, C3 and C4 in the DNA-A like genome, whereas only 1 open reading frame designated as C1 was identified in DNA-β. Further characteristics of each open reading frame were further elucidated. These results provided us information on distribution of monopartite PepYLCV in West Sumatera Indonesia, as well as its genome characteristic that in turn could be used as our start point for development of resistant chili pepper cultivar. 2013/05/31 - 05:57

Tomato (Solanum lycopersicum L.) is one of the world's most widely cultivated
vegetable crops. Among the tomato-inflicting diseases, wilt caused by Ralstonia
solanacearum (Smith) is a major yield-limiting factor. Management of the
disease has been hampered by use of ineffective pesticides and lack of resistant
varieties. This study aimed at using two antagonistic bacteria and three chemical
inducers to inhibit the disease. The dual-culture technique was used to test
the in vitro inhibition of R. solanacearum by two antagonistic bacteria
(Paenibacillus polymyxa MB02-1007 and Paenibacillus macerans MB02-992)
and three chemical inducers (sodium benzoate, ascorbic acid and isonicotinic
acid). The effects of the two antagonistic bacteria and three chemical inducers
on control of Ralstonia wilt and promotion of tomato growth were evaluated
in pots in a randomized block design under greenhouse conditions. The antagonistic
bacteria significantly improved seed germination and seedling vigour of tomato
plants. Disease incidence and the population of Ralstonia solanacearum
in tomato plants were considerably reduced by the two antagonistic bacteria
and the three chemical inducers, singly or in combination, compared to the control.
In particular, the combination of antagonistic bacteria with isonicotinic acid
at 3 mg mL-1 increased height, fresh and dry weight of tomato plants
by more than 89%, while the combination of antagonistic bacteria with sodium
benzoate at 40 mg mL-1 or ascorbic acid at 8 mg mL-1 or
isonicotinic acid at 3 mg mL-1 inhibited tomato bacterial wilt by
more than 72% compared to the control. Overall, this study revealed that chemical
inducers, in combination with antagonistic bacteria, have a powerful effect
on tomato growth promotion and control of tomato bacterial wilt. 2013/05/31 - 05:57

Chilli is an important cash crop and India is the largest grower, consumer
and exporter of dry chillies and other products to over 90 countries around
the world. This crop suffers heavy losses in yield due to many diseases especially
dieback and fruit rot diseases the frequent epiphytotics of the diseases in
the Kashmir valley. During the past few years and extend of damage infelicated
necessitated us to generate basic information on the important aspects like
status, variability, hostrang and integrated management of the disease. Thus,
the present study was undertaken to know the behavior of the disease and biology
of the pathogen so as to device better managemental practices of the diseases
to avoid losses. The objectives of the study were carried out as per the latest
methodologies adopted by various workers in the world. Pathogenic behavior of
twenty isolates of C. capsici, developed from fruits of chilli, was established
following Koch’s Postulates.
Colonies varied in their cultural behavior ranging from cottony to fluffy, mostly
suppressed with regular to irregular margins. Colour of colonies ranged between
white to grey. Growth rate of isolates was between 32.0-67.5 mm. Morphological
studies of isolates revealed variations in their colour, size, shape, acervuli
production, setae size and shape, conidia. Average conidial size varied from
2.23-33.6 μm and average setae size varied from 4.48-177.21 μm. On
the basis of disease reaction expressed by differential hosts, ten groups (races)
of C. capsici were identified. The group 1 comprised of isolates Cc-1,
Cc-15 whereas group 2 included the isolate Cc-2, Cc-6, Cc-16. The Cc-3, Cc-10
were included in group-3 whereas group-4 included the isolate Cc-18, Cc-20,
Cc-12, Cc-9. The group 5 comprised of isolates Cc-13, Cc-14. The group 6 comprised
of Cc-17, Cc-19. The group 7 comprised of isolates Cc-5, Cc-11. Similarly, the
isolate Cc-7 was clubbed under group 8. 2013/05/31 - 05:57

Owing to its high protein content, faba bean (Vicia fabae L.) leaves’
phylloplane harbors many microorganisms besides Botrytis fabae which
could have antagonistic potential. The use of chemical fungicides against chocolate
spot has been a common practice, but negative effects to the environment forces
a search for alternative options. The objective of this study was to explore
fungal isolates residing on faba bean leaves and evaluate their antagonistic
potential against B. fabae. For this matter, 236 leaf samples were collected
from different districts of West Hararghe and Bale zones, which yielded 72 fungal
isolates. These isolates were evaluated for their biocontrol potential against
B. fabae in vitro. ANOVA (Analysis of Variance) for Antibiosis, percent
growth inhibition, growth rate and parasitism tests showed significant difference
(p<0.0001) among fungal isolates. In antibiosis test, two isolates, Trichoderma
harzianum and Penicillium spp. formed higher mean inhibition zone
of 7.33 and 7.00 mm, respectively and the highest mean colony growth inhibition
were recorded from T. harzianum (69%) and T. oblongisporum (58.1%)
over the control. Trichoderma spp. showed higher mean growth rate (14-16.67
mm day-1) than any of other fungal isolates and on the other hand
higher mean diameter of lysed mycelium (12 mm) was recorded from Aspergillus
spp. and Penicillium spp. This study revealed higher distribution of
biocontrol agents and their antagonistic ability over B. fabae, in Ethiopia.
Particularly Trichoderma spp. showed better potential in controlling
B. fabae and can be further evaluated for its commercialization, either
alone or as a component of integrated disease management. 2013/05/31 - 05:57

A leaf bioassay was done in vitro to determine the effects of different mineral salts on the infection of apple powdery mildew. Calcium chloride, cupper sulfate and calcium carbonate led to more than 50% significant reduction in disease severity % and were more effective than ammonium phosphate and potassium dihydrogen phosphate. Golden Delicious and Royal Gala were found susceptible to the disease thus were subjected for post-infection treatment with some systemic fungicides or calcium chloride under field conditions. One week after the foliar spray, Triforine and Triadimenol were more effective than Carbendazim and calcium chloride in reducing the disease amount. Their reduction in disease progress was continued after one month from the day of the foliar spray. Calcium chloride was more effective at an application rate of 10 g L-1 than at 1 g L-1. Calcium chloride treatment did not give long-term efficacy especially in Royal Gala. Therefore, the use of salts as an anti-resistance strategy should be used in a rotation with chemical fungicides or combined with other control measures. 2013/05/31 - 05:57

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is a destructive disease worldwide. Recently it has emerged as a threat to soybean production in the United States (U.S.). There is limited knowledge regarding the genetic diversity and geographic distribution of P. pachyrhizi isolates in the United States. To address this issue, a survey was conducted to define the genetic diversity and possible origin(s) of U.S. isolates. The Internal Transcribed Spacer (ITS) sequence and the ADP-Ribosylation Factor (ARF) gene sequence were amplified and cloned from a collection of 59 isolates. Consequently, the cloned ITS and ARF sequences were subject to phylogenetic analyses. At least five genotypes were identified within the U.S. isolates and most states contained a mixture of isolates. Gauged by the DNA sequences derived from international and archival isolates, two groups of global isolates that are endemic to all continents were identified. This reinforces the hypothesis of a global migration of P. pachyrhizi. However, there are also two groups of isolates that appeared to be present only in Asia, Australia and U.S. This suggests the presence of a possible alternative migratory pathway. One isolate type appeared to be unique to the U.S., suggesting either a unique origin or rapid diversification of isolates collected from the U.S. The data provide the most comprehensive analysis to date of the genetic diversity of P. pachyrhizi isolates in the U.S. 2013/03/21 - 10:37

Melaleuca alternifolia (tea tree), Thymus vulgaris (thyme),
Laurel nobilis (laurel), Mentha x piperita (peppermint), Origanum
vulgare (oregano), Syzygium aromaticum (clove) and Rosmarinus
officianalis (rosemary) essential oils were tested for their antifungal
activity to investigate the possibility of their use for legumes seed treatment.
The ability of the seven oils to inhibit mycelial growth was studied by in-vitro
assay on agar medium containing different concentrations of the essential
oils. Six seed-borne pathogen fungi of large interest Peyronellaea pinodella,
Peyronellaea pinodes, Diaporthe phaseolorum var. caulivora, Phomopsis
longicolla, Ascochyta lentis and Colletotrichum gloeosporioides
were transferred on the modified medium in order to test the oils antifungal
activity, by calculating the percentage of Mycelial Growth Inhibition (MGI)
and the Minimum Inhibitory Concentration (MIC). Results showed a clear reducing
effect of the oils on fungal growth, that was dose-dependent and it differed
depending on the fungal species. The most effective were thyme, clove, peppermint
and oregano oils. Therefore, the essential oils tested can be considered very
interesting for developing alternative natural fungicides to the synthetic chemicals
and can be potentially used in organic agriculture to prevent and control seed-borne
diseases for safe and low environmental impact seed treatments. 2013/03/21 - 10:37

This study was conducted under green house conditions during summer growing seasons 2010 and 2011, to evaluate the response of 21 Jordanian tomato land races (accessions) against the vascular wilt fungus Fusarium oxysporum f.sp. lycopersici. Accessions were provided by the National Center for Agricultural Research and Extension (NCARE). Inoculation with the fungus was carried out by using the root dip method. Parameters considered in this study were discoloration, yellowing and fresh weight. Both discoloration and yellowing were measured, recorded according to 1-5 scale and their results ranged from 1-3.5, while fresh weight ranged from 33.1-76.5 g for treatments compared with 41.0-98.8 g for controls. Nine out of 21 studied tomato accessions were significantly different from other accessions and appeared to be resistant to the fungus under experimental conditions according to the 1-5 scale. Most of the resistant accessions were from the slow growing lines, while most of the fast growing accessions were susceptible. The study concluded that resistant accessions are promising ones to be used as root stocks for cultivated tomato varieties. 2013/03/21 - 10:37

Wheat stem rust severity was determined using stratified simple random sampling
technique and physiological races of Puccinia graminis f.sp. tritici
were determined using the 20 North American wheat stem rust differentials.
Results revealed a significant variation in wheat stem rust severity in the
region. Lower wheat stem rust severity of 12.5% was observed in high altitude
areas of Kipkabus having more than 2200 m above sea level. High wheat stem rust
severity of 34 and 32% was observed in Mois Bridge and Moiben, respectively.
These areas had lower altitude of less than 1900 mean sea level. Four wheat
stem rust races were reported in this region. The predominant race was TTKST
(Ug99+Sr24) at 66.7% predominance, followed by race TTKSK (Ug99)
at 21.1%, race PTKST (Sr31+Sr24-Sr21) at 10.5% and race TTTSK (Ug99+Sr36)
at 1.8%. A new race PTKST was reported at Chepkoilel, Moiben and Mois Bridge.
There was no significant correlation (r = 0.398) of stem rust severity and race
diversity. However, there was a significant negative correlation (r = -0.461)
of race diversity and altitude and a highly significant negative correlation
(r = -0.713) of altitude and stem rust severity. The study concluded that wheat
stem rust severity varied depending on altitude and location, and four races
are present in North Rift region of Kenya, where the predominant race is TTKST
(Ug99+Sr24). 2012/11/07 - 22:39

Sorghum rust is a common disease in most of the sorghum-growing areas of the
world, which increase susceptibility to other major diseases. Although, plant
resistance is the best control strategy, today, a limited number of resistance
sources are available. Therefore, identification of new resistance sources is
essential to extend the control of the disease. In this study 68 sorghum accessions
from the Zimbabwe collection maintained by the USDA-ARS, Plant Genetic Resources
Conservation Unit at Griffin, Georgia were evaluated in Isabela, Puerto Rico
during two planting seasons in 2011 to identify new sources of rust resistance.
Across the two growing seasons, 12 accessions showed resistance, 15 accessions
exhibited a moderately susceptible response and 41 accessions showed a susceptible
response. Variation in disease response was observed within and between experiments
for 37 accessions. No rust infection was detected on PI482787 across the two
growing seasons, while accession PI482795 exhibited the highest rust infection.
This study identified new sources of rust resistance and shows that PI482787
possess gene(s) for rust resistance and that this accession could be used in
sorghum improvement breeding programs. 2012/11/07 - 22:39

In Indonesia, yellow streak and necrosis symptoms were observed on banana plants.
By species-specific PCR, infection with both Banana streak Mysore virus (BSMyV)
and/or Banana streak OL virus (BSOLV) was suspected. To confirm whether the
DNAs were derived from viral particles or banana endogenous viruses (BEVs),
we used combination of two methods: PCR-based assay using long and semi-nested
PCR and southern hybridization assay using total DNA. Both of those detection
methods revealed that these two samples were infected only by exogenous BSMyV
but not BSOLV. This study is the first report of the identification of BSMyV
in Indonesia. 2012/11/07 - 22:39

Aquilaria malaccensis Lamk. (Locally known as Sasi or agar plant) is
a precious floral wealth of North-East India and has been identified as a potential
aromatic plant of this region. It is the principal producer of the dark brown
agarwood or eaglewood, produced within heartwood as a result of host-fungus
interaction. The essential oil from agarwood is valued for preparation of several
pharmaceutical and cosmetic products. Due to the abundance of agar trees in
North East India, the trade of agar has become a fascinating industry in this
region and earned a name of its own in the world market. During the survey in
the nursery of Rain Forest Research Institute, Jorhat Aquilaria malaccensis
seedlings were found to be infected with a leaf spot disease. This study
described the symptomatology and etiology of the disease. The pathogenicity
studies revealed the cause of the disease as Corynespora cassiicola (Bark
and Curt). This disease is recorded for the first time in Aquilaria
malaccensis. 2012/11/07 - 22:39

Cassava mosaic disease epidemiology and molecular characterization of the related viruses monitored during this study in the Sud-Kivu region, Democratic Republic of Congo. Collected epidemiologic data showed a negative correlation with the altitude (elevation) on the disease incidence and its vector population. Disease incidence was 9.5 to 37.8% associated to less than 3 insects per leaf when the elevation is higher than 1500 m while 65 to 100% and more than 10 insects per leaf were recorded where elevation was less than 1000 m. No impact of rainfall has been recorded. Associated molecular cassava begomovirus diagnostic focused on AC2 and AC4 genes revealed only two species occurring in this area, African Cassava Mosaic Virus (ACMV) and East African cassava mosaic virus-Uganda (EACMV-UG) with more EACMV-UG and mixed infections in low elevation area while ACMV were predominant in high elevation sites. Phylogeny analysis revealed a dual coexistence of indigenous and Ugandan spread among ACMV isolates while all EACMV isolates were restricted to Ugandan spread (95 to 100% of amino acids identity). No recombination was revealed in this study, isolates diversity was restricted to nucleotide substitution. 2012/03/21 - 20:58

Five cowpea cultivars, ITO3K -316-1, ITO4K-217-5, IT06K-154-1, IT99K-216-44 and IT03K-369-3, obtained from the International Institute of Tropical Agriculture, Ibadan were screened for resistance to Macrophomina phaseolina infection using two methods of inoculation viz, pouring of spore/mycelia suspension in the soil and wrapping of inoculum meal around wounded lower stem of the seedlings. Cowpea cultivar ITO4K-217-5 was resistant to the pathogen in both inoculation methods while the other four cowpea cultivars i.e., ITO3K-316-1, IT99K-216-44, ITO6K-154-1 and ITO3K-369-3 showed varying degree of susceptibility to the pathogen in both inoculation methods. 2012/03/21 - 20:58

Archetypal fungal resistance is marked by deform macroscopic growth on artificial medium supplemented with fungicides and the overexpression of resistance proteins weaponries at the molecular level. The interaction of Fusarium oxysporum f.sp. dianthi. with fungicides viz., copper oxychloride, metalaxyl-mancozeb and, mancozeb under heat-stress condition was studied. We evidence the pathogen interrelatedness to elude combine heat and fungicides stress is chiefly governed by the differential over expression of a 22.9 kDa Resistant Heat Shock Protein (RHSP) and a 26.3 kDa housekeeping protein (HKP). Of the assayed fungicides, resistant protein suppression was a function of temperature rise acting as a positive variance for copper oxychloride; and as a negative variance for mancozeb and metalaxyl-mancozeb. This first report suggests predicting field temperature prior to application of fungicide of choice is keyed to avert resistance resurgence. We infer within the context of global warming, the interaction of F. oxysporum f.sp. dianthi with fungicides inherently fluctuates and lends credence for the expression of adaptive RHSP responsible for its resiliency, a predicament for the farmers cry. 2012/03/21 - 20:58

Infestation of rice by the leaf blast disease caused by Pyricularia oryzae is frequent and results in severe yield losses and high production costs. Silicon has been reported to have potential for controlling the blast disease in rice. The objectives of this study were to determine the effects of silicon in suppressing the blast disease and increasing the grain yield of organic rice in northeast Thailand. Field experiments were conducted in farmers’ fields in two locations in Northeast Thailand, Buriram (experiment 1) and Surin (experiment 2) provinces. Both experiments used a randomized complete block design with four replications. Treatments consisted of four silicon application rates of 0, 250, 500 and 1,000 kg ha-1. Results showed that silicon applied to rice suppressed occurrence of the blast disease. Values of a severity index of leaf blast and neck blast were significantly decreased when silicon was applied at the rate of 250 to 1,000 kg ha-1 in comparison with the control treatment without silicon in both locations. At the highest silicon application rate, 1000 kg ha-1, leaf and neck blast severity were reduced by 83 and 75% in experiment 1 and 81 and 77% in experiment 2, respectively. Grain yield when silicon was applied was 19-43% higher than the control in experiment 1 and 2-14% higher than the control in experiment 2. The maximum grain yield was obtained at the rate of 1,000 kg ha-1 in both locations (4,538 and 4,070 kg ha-1 in experiments 1 and 2, respectively). The yield obtained when silicon was applied at the rate of 1000 kg ha-1 was not significantly different from that obtained at the rate of 500 kg ha-1 in experiment 1, but it was significantly higher in experiment 2. 2011/12/11 - 09:52

Diaporthe/Phomopsis Complex (DPC) can infect soybean seed and reduce its germination in the field and also survive on the seed during storage. Ten soybean seed lots which were stored at 0°C for up to 13 years were used to evaluate the percentage of DPC infection on them and also to identify the DPC isolates. Morphological and molecular methods were used to determine the longevity and frequency of DPC isolates in stored soybeans seeds. Conventional and nested Polymerase Chain Reaction (PCR) was used for amplification of pure cultures and seed lots. The longevity of isolates in storage was found to be <9 years which suggested that Diaporthe/Phomosis sp., can survive up to 9 years in cold storage (0°C). Six isolates of DPC were detected, identified and characterized based on morphological and molecular methods in soybean seeds for the first time in Malaysia. Most of the isolates identified belonged to Phomopsis longicolla and only one isolate identified from Diaporthe Phaseolorum var. sojae. All isolates that were identified using morphological technique were confirmed using molecular method and registered in national center of biotechnology information (NCBI). The result of this study showed that DPC isolates can survive for long time in storage. 2011/12/11 - 09:52

An experiment was conducted at “Green House Project Farm”, Watagoda, Sri Lanka from April 2011 up to August 2011 to identify the causal organisms and suggest an integrated control approach for wilting of bell pepper plants in green houses. Pathogens were isolated from infected plant parts and soil media. Six media treatment methods including Carbendazim only, Metham Sodium only, Plastic potted, Thiram and Carbendazim alternatively, Thiram only and Steam, each with two levels of irrigation including full and half irrigated were tested in field in a seven in to two factorial RCBD design. Statistical analysis of data was done by Minitab 15. Under stereo microscopic observation Fusarium spp., Pythium spp. and Phytophthora spp. were the prominent pathogenic species. Oomycetes (Pythium spp. and Phytophthora spp.) were significantly detected in the roots and fungi Fusarium spp. were detected in stem parts and soil. It was appeared that the primary infection of Pythium spp. and Phytophthora spp. killed the root cells resulting root rot. Secondary infection of Fusarium spp. through broken root cells develops up to the stem and above ground parts, hindering the vascular flow and finally causing withering of the plant in green houses. The lowest wilt percentage was recorded in Metham and Steamed treated plants. The successful media sterilization was by Steaming and followed by Metham. Irrigation levels were not significantly correlated with plant wilting. However, the results of the study suggested that wilt suppression could be achieved by placing the steam treated plants disconnecting the contact with ground. 2011/12/11 - 09:52

An experiment was conducted at “Green House Project Farm”, Watagoda, Sri Lanka from April 2011 up to August 2011 to identify the causal organisms and suggest an integrated control approach for wilting of bell pepper plants in green houses. Pathogens were isolated from infected plant parts and soil media. Six media treatment methods including Carbendazim only, Metham Sodium only, Plastic potted, Thiram and Carbendazim alternatively, Thiram only and Steam, each with two levels of irrigation including full and half irrigated were tested in field in a seven in to two factorial RCBD design. Statistical analysis of data was done by Minitab 15. Under stereo microscopic observation Fusarium spp., Pythium spp. and Phytophthora spp. were the prominent pathogenic species. Oomycetes (Pythium spp. and Phytophthora spp.) were significantly detected in the roots and fungi Fusarium spp. were detected in stem parts and soil. It was appeared that the primary infection of Pythium spp. and Phytophthora spp. killed the root cells resulting root rot. Secondary infection of Fusarium spp. through broken root cells develops up to the stem and above ground parts, hindering the vascular flow and finally causing withering of the plant in green houses. The lowest wilt percentage was recorded in Metham and Steamed treated plants. The successful media sterilization was by Steaming and followed by Metham. Irrigation levels were not significantly correlated with plant wilting. However, the results of the study suggested that wilt suppression could be achieved by placing the steam treated plants disconnecting the contact with ground. 2011/12/11 - 09:52

Lentil is one of the most important legume crops in the world, especially in developing countries. In Egypt, root rot and wilt are the most important fungal diseases. Greenhouse and field experiments were conducted to study the effect of Molybdenum (Mo) or Cobalt (Co) on lentil pathogens (Rhizoctonia solani and Fusarium oxysporum) and nitrogen fixation compared with fungicide Rizolex T50. Lentil seeds (cvs. Giza 4 and Giza 9) were soaked 8 h in Mo or Co at concentration of 2 and 5 ppm before seeding while Rizolex T50 was used as seed-coating at 3 g kg-1 seeds. A split plot design with three replicates was used under greenhouse conditions. Results showed that damping off significantly increased in Giza 9 compared to Giza 4. While both Mo and Co decreased it in both cultivars; low level (2 ppm) was more effective. In the field, Mo and Co treatments showed significant decrease in pre and post-emergence damping off as well as dead plants (resulted from root rot and wilt). Additionally, plant height of lentil varieties showed significant increase by Mo (2 ppm) and Co (2 ppm) treatments. Different concentrations of Mo and Co were found to induce high root nodules, nitrogenase activity and nitrogen fixing bacteria. Seed yield increased significantly by Mo and Co treatments except Mo (5 ppm) on Giza 4 variety in second season. Soaking lentil seeds in Mo or Co at 2 ppm is recommended to be incorporated into the production program of lentil to decrease root rot and wilt diseases as well as improve growth and productivity. 2011/09/23 - 16:56

Watermelon Mosaic Virus (WMV) is a Potyvirus with a worldwide distribution. This virus causes serious economic losses in many cucurbits in Iran. To study relative incidence and molecular variability of WMV, 620 samples of cucurbit plants were collected from the different fields and cucumber greenhouses in some regions of Iran. Three hundred and three samples were infected by WMV in DAS-ELISA using specific polyclonal antibody (The rate of infection was 48.8%). In RT-PCR assay with specific primers of WMV, a single band of about 825 bp in length was produced from the samples. The Coat Protein (CP) region of the genome from 15 representative isolates were sequenced and compared with the sequences available in GeneBank. The identity of WMV CP nucleotide sequences of the 15 Iranian isolates ranged from 95.8 to 99.2%. According to this research Iranian isolates have high variation in CP gene. In most cases, geographical isolation is consistent with the phylogenetic grouping. Molecular weights of coat protein using SDS-PAGE were estimated at 34100 Da. Data shown in this study represent the occurrence of WMV based on ELIZA, RT-PCR and CP gene analyses in some region of Iran. These results make it possible to have a better understanding of the development of WMV disease in Iran. 2011/09/23 - 16:56

Virus diseases are a limiting factor in cowpea production in all agro-ecological zones of Nigeria and yield reductions of between 80-100% have been reported. Some cowpea varieties show resistance to viruses, cultural practices such as varying plant population have been found useful in the control of these viral pathogens. Field experiments were conducted in the 2009 and 2010 cropping seasons to evaluate the effect of crop variety and varying planting density on the incidence of common viral diseases of cowpea. Vigna unguiculata (L.) Walp in the Southern guinea savannah agro-ecology of Nigeria. This is to identify tolerant varieties and an optimum planting density that could lead to lower viral incidence and high crop yields. A split-plot fitted into a randomised complete block experimental design with three replications was established with three cowpea cultivars (IT89KD-288, IAR-48 and Ife brown), in the main plots and three planting densities (25x75, 50x75 and 75x75 cm) in the sub-plots. The results of the study indicated that variety and planting density had significant effect on viral disease incidence. The lowest incidence was in variety IT89KD-288 (10.3%) while the highest was in variety IAR-48 (28.6%). The lowest mean incidence was also in plots under planting density of 25x75 cm. However, planting at a mid-level density of 50x75 cm with variety IT89KD-288 outperformed the other combinations for yields and is therefore, recommended. 2011/09/23 - 16:56

Primer pairs XOR-F/XOR-R2 was used for rapid identification and differentiation of thirty strains of Xanthomonas oryzae pv. oryzae (Xoo) were collected from rice fields in Penang, Kedah, Selangor and Melaka during the period from 2008 to 2010. Purified DNA was extracted using a modified CTAB method and was used in the PCR. Four hundred and seventy bp product was amplified from DNA of 30 strain using XOR-F/XOR-R2 primer pairs. Sequence similarities of the intergenic region in the 16S-23S rDNA in the Malaysian strains were as high as 99-100%. Cluster analysis based on the sequencing shows that the strains are grouped one main cluster and four groups. The minimum role of varietal influence on strain variability is partly due to the almost homogenous planting of two popular rice varieties in Peninsular Malaysia during the period of the study. On the other hand, phylogenetic analysis by using intergenic region 16S-23S divided the strains into one main cluster and four groups. The first group is represented by isolates collected from Penang and the second groups from Selangor. The third and fourth groups represented strains collected from Melaka and Kedah, respectively. The present study confirmed that direct DNA extraction from infected rice tissue by using CTAB method, followed by PCR effective methods for the identification of Xoo. Further more the results indicated that strains differentiation may be affected by the geographical areas. 2011/07/11 - 23:38

The present study was aimed to identify root rot pathogens of blue pine (Pinus wallichiana) in Kashmir and develop appropriate eco-friendly disease management strategy. During nursery surveys, Fusarium oxysporum, Rhizoctonia solani and Macrophomina phaseolina were found root rot incitants with isolation frequency of 47.3, 29.7 and 13.0%, respectively. Locally isolated antagonists inflicted 33.0-73.3 and 29.5-70.8% mycelial growth inhibition in F. oxysporum and R. solani, respectively, with Trichoderma harzianum and T. viride proving most effective. The mycorrhizal fungi, Pisolithus tinctorius and Laccaria laccata, significantly inhibited the growth of R. solani and F. oxysporum by 46.2 and 45.4 and 44.7 and 43.7%, respectively. Bioagents significantly improved seedling biomass and root/shoot length. Mycorrhizal plants showed 5-13 fold higher rhizosphere phosphatase activity than non-mycorrhizal ones. Four effective fungal bioagents, inoculated individually and in combination with pathogen under nursery conditions, significantly improved seedling biomass and height with maximum gain by P. tinctorius and L. laccata. Rhizoctonia infection decreased biomass and seedling height by 32.6 and 35.4%, whereas bioagents mitigated the pathogenic effect. The bioagents in R. solani/F. oxysporum-infected soil significantly improved seedling biomass and height over pathogen treatments alone. P. tinctorius and L. laccata exhibited 44.2 and 39.1% root colonization in comparison to 19.5-24.2% in presence of pathogens. The study revealed that bioagents, especially mycorrhizae, effectively mitigate root rot in blue pine and can be efficiently exploited in integrated disease management module. 2011/07/09 - 08:26

Apple scab, caused by Venturia inaequalis, is one of the most damaging diseases worldwide on apple and is currently managed mainly by scheduled applications of fungicides. The aim of the present study was to understand the pathogen population structure in Jammu and Kashmir which is important for breeding and deployment of resistant cultivars. Twenty-seven isolates of V. inaequalis were sampled from commercial apple growing areas to estimate differences in pathogen populations using Random Amplified Polymorphic DNA (RAPD) 10 -and 20-mer primers. RAPD data analysis grouped 27 isolates in to three major clusters accommodating 10, 10 and 7 isolates each. The categories did not follow any geographic or source cultivar pattern. Allele frequencies among the three populations varied from 0.00 to 1.00. The average genetic diversity within each population (HS) over all loci studied was 0.21, 0.23 and 0.20 in Ganderbal, Pulwama and Srinagar, respectively thereby showing high genetic diversity within each population. The average genetic differentiation at a single locus among all sampled populations (GST) was 0.12. The overall gene flow (Nm) was 3.54 while the gene flow values at a single locus ranged from 0.70 to 69.32. Pair-wise genetic differentiation values (FST) among all loci were low, thereby indicating high diversity among the three populations. Analysis of molecular variance (AMOVA) obtained after clustering the isolates at district level showed highly significant genetic differentiation among populations with 5.46 and 94.54% genetic variability recorded among and within district populations, respectively. Population genetic analysis of V. inaequalis is the first molecular analysis of this pathogen from the India and especially from Jammu and Kashmir, a north-western Himalayan state of India. 2011/07/09 - 08:26

Garlic extract is well known for its antibacterial and antifungal activity and is used to treat several plant pathogens. Pythium sp. was isolated from infected tomato seedlings grown in Jordan Valley (Jordan) and the species was identified as Pythium ultimum using morphological and molecular methods. The fungicidal activity of garlic extract with different concentrations in controlling the growth of the isolated Pythium sp. was determined in vitro. The control activity was highly dependent on Garlic extract concentration. For instance, undiluted garlic extract showed the highest control activity with no growth as compared to the biotic control without the extract whereas diluted garlic extracts 10 and 5% reduced the fungal growth to 15.5 and 41%, respectively. The results of this study show that garlic extract could successfully control Pythium ultimum on tomato seedlings and is considered as an environmentally friendly product. 2011/07/09 - 08:26

In the present study, we assessed the pathogenicity of the prevalent strains of Rice Yellow Mottle Virus (RYMV) present in Eastern Uganda and identified suitable donors for durable resistance among rice cultivars. Screenhouse studies were conducted using eight isolates of the virus against 16 rice cultivars. Isolate aggressiveness and cultivar resistance were assessed in terms of disease severity and percentage stunting following mechanical inoculation by the finger-rub technique. Highly significant differences (p<0.001) between rice cultivars for both parameters revealed the occurrence of different genetic factors for resistance among the rice cultivars. Mean disease severity and percentage stunting ranged between 0.9-9.0 and -1.1-32.4%, respectively for individual cultivars. The absence of significant isolate-by-cultivar interaction suggests a race-non-specific resistance. No significant differences in aggressiveness were obtained between isolates, indicating limited pathotype diversity in Eastern Uganda as evidenced by the absence of mega-environments among the prevalent strains. Based on cultivar resistance ranking, three O. sativa subspecies japonica (NERICA6, ITA257 and ITA325) and two O. sativa subspecies indica (WAC116 and WAC117) were identified as the potential sources of resistance for improving susceptible local varieties. The confirmed resistance breakdown in GIGANTE has important implications for plant breeding and disease control strategies. Therefore, pyramiding different sources of resistance is recommended for enhanced durability of resistance. In addition, the use of sufficient prerelease challenge by the combination of isolates with different levels of aggressiveness will delay the rise of susceptibility in deployed resistant cultivars. 2011/04/27 - 14:34

This study was conducted to examine the antifungal activity of some agriculture wastes (rice straw, maize and cotton wastes) against Rhizoctonia solani which is the causal agent of root rot of soybeans. For this target, it is logical start first to test the effects of different agriculture wastes extracts on the growth of R. solani under laboratory conditions, while most of the tested agriculture wastes extracts were exhibited antifungal activities against R. solani on Potato Dextrose Agar medium, so we applied them under greenhouse conditions. Furthermore, we determined the relation between the phenols, polysaccharides and protein content of the tested agriculture wastes and their antifungal activities. The results showed that maize wastes were the most active of all the tested wastes. It could be concluded from the obtained data the use of the tested biotic factors can be fruitful for controlling soybean rot root induced by R. solani. 2011/04/27 - 14:34

Phomopsis Seed Decay (PSD) is detrimental for seed quality in soybean. In this study, three varieties of soybean were evaluated to determine their sensitivity to PSD and its influence on seed quality. These varieties were planted in a factorial experiment with three replication in two plant densities and two seasons in University Putra Malaysia. The incidence of Phomopsis was determined using culture plate method. Seed quality was tested using standard germination test, tetrazolium test and electrical conductivity. Most colonies were morphologically similar with Phomopsis longicolla. Infection to Phomopsis and seed viability was significantly different between soybean varieties and plant densities in two seasons. The AGS 190 with 46% showed the most percentage of Phomopsis in higher plant density in the second season. Pershing had 10% infection in lower plant density in the first season and showed more tolerance to Phomopsis in this study. Higher plant density caused higher infection to PSD, lower percentage of seed viability and more electrical conductivity. Standard germination and tetrazolium test were 76 and 72% in higher plant density respectively. Electrical conductivity was 83 μS cm-1 g-1 in higher plant density whereas it was 68 μS cm-1 g-1 in lower plant density. Phomopsis incidence showed negative correlation with seed viability and it was positively correlated with electrical conductivity. Based on these relationships, Pershing with its low Phomopsis infection showed the highest seed viability. The values for viability were 84 and 82%. This study indicates that the incidence of Phomopsis seed decay is usually dependent on field environments and planting densities. The severity of infection is also dependent on the variety. 2011/04/27 - 14:34