Showing papers on "Leaf spot published in 2005"
TL;DR: Chitin-supplemented application of B. circulans GRS 243 and S. marcescens GPS 5 resulted in improved and stable control of LLS in a repeated field experiment and increased the pod yields by 62 and 75%, respectively, compared with the control.
Abstract: Kishore, G. K., Pande, S., and Podile, A. R. 2005. Biological control of late leaf spot of peanut (Arachis hypogaea) with chitinolytic bacteria. Phytopathology 95:1157-1165. Late leaf spot (LLS), caused by Phaeoisariopsis personata, is a foliar disease of groundnut or peanut (Arachis hypogaea) with high economic and global importance. Antifungal and chitinolytic Bacillus circulans GRS 243 and Serratia marcescens GPS 5, selected among a collection of 393 peanut-associated bacteria, were applied as a prophylactic foliar spray and tested for control of LLS. Chitin-supplemented application of B. circulans GRS 243 and S. marcescens GPS 5 resulted in improved biological control of LLS disease. Supplementation of bacterial cells with 1% (wt/vol) colloidal chitin reduced lesion frequency by 60% compared with application of bacterial cells alone, in the greenhouse. Chitinsupplemented application of GRS 243 and GPS 5 also resulted in improved and stable control of LLS in a repeated field experiment and increased the pod yields by 62 and 75%, respectively, compared with the control. Chitin-supplemented application of GPS 5 was tested in six onfarm trials, and the increase in pod yields was up to 48% in kharif (rainy season). A 55-kDa chitinase was purified from the cell-free culture filtrate of GPS 5 by affinity chromatography and gel filtration. Purified chitinase of S. marcescens GPS 5 (specific activity 120 units) inhibited the in vitro germination of P. personata conidia, lysed the conidia, and effectively controlled LLS in greenhouse tests, indicating the importance of chitinolysis in biological control of LLS disease by GPS 5.
119 citations
Journal Article•
TL;DR: Ten potent strains of marine actinomycetes isolated from the sediment samples drawn from mangroves, estuary, sand dune, and industrially polluted coast may prove to be the potent source for isolation of agrobased fungicides.
Abstract: A total of 160 isolates of marine actinomycetes were isolated from the sediment samples drawn from mangroves, estuary, sand dune, and industrially polluted coast Of these, mangrove sediments were rich sources of marine actinomycetes Each isolate was tested against four phytopathogenic fungi, viz Rhizoctonia solani, Pyricularia oryzae, Helminthosporium oryzae (causing sheath blight, blast and leaf spot diseases of rice) and Colletotrichum falcatum (causing red rot disease of sugar cane) About 51% of isolates were found effective against H oryzae and P oryzae, 31% against R solani, and 125% against C falcatum Of 160 isolates, 10 showed a potent activity against all the fungi tested These isolates appeared to produce high antifungal compounds at 120 hrs of incubation period of production medium culture Glucose and soybean meal were the best carbon and nitrogen sources, respectively and 175 ppt was the best salinity level for maximum antibiotic production Cylinder plate method was found better for antifungal assay than the disc diffusion method Based on the morphological and culture characteristics, the potent strains were identified as the species belonged to the genus Streptomyces These strains may prove to be the potent source for isolation of agrobased fungicides
79 citations
TL;DR: The selected genes identified by microarray analysis were validated by real-time PCR and were more greatly expressed in the resistant genotype as a result of response to the challenge of C. personatum than in the susceptible genotype.
Abstract: Late leaf spot disease caused by Cercosporidium personatum is one of the most destructive foliar diseases of peanut (Arachis hypogaea) worldwide. The objective of this research was to identify resistance genes in response to leaf spot disease using microarray and real-time polymerase chain reaction (PCR). To identify transcripts involved in disease resistance, we studied the gene expression profiles in two peanut genotypes, resistant or susceptible to leaf spot disease, using cDNA microarray containing 384 unigenes selected from two expressed sequenced tag (EST) cDNA libraries challenged by abiotic and biotic stresses. A total of 112 spots representing 56 genes in several functional categories were detected as up-regulated genes (log(2) ratio > 1). Seventeen of the top 20 genes, each matching gene with known function in GenBank, were selected for validation of their expression levels using real-time PCR. The two peanut genotypes were also used to study the functional analysis of these genes and the possible link of these genes to the disease resistance trait. Microarray technology and real-time PCR were used for comparison of gene expression. The selected genes identified by microarray analysis were validated by real-time PCR. These genes were more greatly expressed in the resistant genotype as a result of response to the challenge of C. personatum than in the susceptible genotype. Further investigations are needed to characterize each of these genes in disease resistance. Gene probes could then be developed for application in breeding programs for marker-assisted selection.
71 citations
TL;DR: Phylogenetic analysis revealed that isolates of Alternaria alternata causing black rot of citrus were associated with six well-supported evolutionary lineages, demonstrating that small-spored Alternaria isolates associated with different ecological niches on citrus and other plant hosts are potential black rot pathogens.
Abstract: Phylogenetic analysis revealed that isolates of Alternaria alternata causing black rot of citrus were associated with six well-supported evolutionary lineages. Isolates recovered from brown spot lesions on Minneola tangelo, leaf spot lesions on rough lemon, and healthy citrus tissue and noncitrus hosts were related closely to isolates from black-rotted fruit. Phylogenies estimated independently from DNA sequence data from an endopolygalacturonase gene (endoPG) and two anonymous regions of the genome (OPA1-3 and OPA2-1) had similar topologies, and phylogenetic analysis was performed on the combined data set. In the combined phylogeny, isolates from diverse ecological niches on citrus and noncitrus hosts were distributed in eight clades. Isolates from all lineages, regardless of ecological or host association, caused black rot in fruit inoculation assays, demonstrating that small-spored Alternaria isolates associated with different ecological niches on citrus and other plant hosts are potential black rot pathogens. These data also indicated that the fungi associated with black-rotted fruit do not form a natural evolutionary group distinct from other Alternaria pathogens and saprophytes associated with citrus. The use of the name A. citri to describe fungi associated with citrus black rot is not justified and it is proposed that citrus black rot fungi be referred to as A. alternata.
56 citations
TL;DR: Tetraconazole and pyraclostrobin, when applied alone, consistently provided effective Cercospora leaf spot control and resulted in high sucrose yield.
48 citations
TL;DR: The results suggest that the rapid increase in gray leaf spot severity generally observed during mid- and late summer may be due to favorable conditions for lesion expansion during this period.
Abstract: Controlled environment studies were conducted to determine the effects of temperature on the expansion of lesions of gray leaf spot, and the effects of temperature and relative humidity on...
47 citations
TL;DR: Five different timings of fungicide applications for control of common leaf-spot diseases and FHB were compared and whether the tested HRSW cultivars could be grouped based on their disease ratings to formulate recommendations for the use of fungicides were evaluated.
Abstract: The optimum timing of fungicide applications for control of leaf-spot diseases in hard red spring wheat (HRSW) is reported to be at Zadok's growth stage 39 (GS 39; flag leaf collar visible), while the optimum timing for suppression of fusarium head blight (FHB) is at GS 60 (beginning of anthesis). The objectives of this research were the following: (i) to compare five different timings of fungicide applications for control of common leaf-spot diseases and FHB and (ii) to evaluate whether the tested HRSW cultivars could be grouped based on their disease ratings to formulate recommendations for the use of fungicides. Across cultivars, the optimum timing of a fungicide application to control leaf diseases was at GS 60 rather than at GS 39. Waiting until flowering did not sacrifice control of the leafspot diseases or grain yield. The application of one half of the labeled rate of Stratego at GS 15 (fifth leaf unfolded) in combination with the labeled rate of Folicur at GS 60 tended to provide the best control...
38 citations
TL;DR: It is demonstrated that np-BNR isolates can protect cotton from infections caused by both root and leaf pathogens and that disease control was superior to that observed with a chemical inducer.
Abstract: Recent reports have shown induction of resistance to Rhizoctonia root rot using nonpathogenic strains of binucleate Rhizoctonia spp. (np-BNR). This study evaluates the biocontrol ability of several np-BNR isolates against root and foliar diseases of cotton in greenhouse trials, provides evidence for induced systemic resistance (ISR) as a mechanism in this biocontrol, and compares the disease control provided by np-BNR with that provided by the chemical inducer benzothiadiazole (BTH). Pretreatment of cotton seedlings with np-BNR isolates provided good protection against pre- and post-emergence damping-off caused by a virulent strain of Rhizoctonia solani (AG-4). Seedling stand of protected cotton was significantly higher (P < 0.05) than that of nonprotected seedlings. Several np-BNR isolates significantly reduced disease severity. The combination of BTH and np-BNR provided significant protection against seedling rot and leaf spot in cotton; however, the degree of disease reduction was comparable t...
37 citations
34 citations
TL;DR: It is suggested that producing vegetable seedlings in FCPB mix or compost-based substrates may provide initial protection against bacterial leaf spot pathogens, as vermiculite and a highly decomposed sphagnum peat mix consistently failed to suppress these diseases.
Abstract: Compost-amended substrates offer the potential for management of diseases caused by soilborne as well as foliar plant pathogens. In this study, the efficacy of composted pine bark mix fortified with the biocontrol agent Trichoderma hamatum 382 (FCPB) against bacterial leaf spot of radish, lettuce, and tomato under controlled environment conditions was evaluated. Plants grown in the FCPB mix and inoculated with bacterial leaf spot pathogens were less severely diseased than plants grown in commercial peat mix or vermiculite. In some cases, plants were also grown in a composted cow manure mix or in a steam-treated compost-amended greenhouse soil, and these plants were also less severely diseased. Infected radish and tomato plants grown in these compost-amended substrates also harbored significantly smaller populations of Xanthomonas campestris pv. armoraciae and Xanthomonas campestris pv. vesicatoria, respectively. The disease-suppression effect of the FCPB mix was lost by autoclaving and restored by reinocu...
33 citations
TL;DR: A telomere probe revealed that the chromosome ends of the very same isolates are highly divergent, with most isolates sharing less than 20% fingerprint similarity with any other isolate, consistent with the gray leaf spot pathogens having a recent evolutionary origin.
Abstract: SUMMARY The gray leaf spot disease of perennial ryegrass and tall fescue is caused by the fungus Magnaporthe oryzae (anamorph = Pyricularia oryzae). A collection of single-copy and repetitive DNA markers was used to investigate genetic diversity among 22 isolates of the gray leaf spot pathogen. The single-copy DNA markers revealed only three polymorphisms among 95 restriction fragments spanning approximately 0.6% of the genome. In addition, Southern hybridization analysis and mating tests revealed that all isolates possessed the MAT1-2 mating-type allele. Fingerprinting of repetitive DNA loci using the Pot2 and MGR583 probes also revealed a high degree of genetic similarity (> 85%) among isolates. These data are consistent with the gray leaf spot pathogens having a recent evolutionary origin. In contrast to the results obtained with probes for internal chromosome loci, a telomere probe revealed that the chromosome ends of the very same isolates are highly divergent, with most isolates sharing less than 20% fingerprint similarity with any other isolate. Telomere mutations arise extremely frequently and changes in telomere fingerprint profiles were readily observed during vegetative growth and among cultures derived from single spores isolated from agar medium and from lesions on perennial ryegrass leaves.
TL;DR: Because most U.S. maize hybrids are resistant, and PLS develops late in the grain-filling period, its potential to cause substantial losses in the United States appears limited at this time.
Abstract: The ability of Phaeosphaeria leaf spot (PLS) to reduce yields of maize was evaluated over two winter growing seasons in southern Florida. Nine commercial maize hybrids, varying in reaction...
TL;DR: In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year.
Abstract: In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (>/=5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P 0.05).
TL;DR: It is demonstrated that safflower is a new host of C. beticola, whereas sugar beet is susceptible to Cercospora carthami.
Abstract: Safflower is an oilseed crop adapted to the small-grain production areas of the western Great Plains, including the Northern Plains Area (NPA). In the NPA, safflower production is being evaluated for potential rotation with sugar beet. Safflower is susceptible to Cercospora carthami, whereas sugar beet is susceptible to C. beticola C. carthami has not been observed on safflower in the NPA but C. beticola is ubiquitous on sugar beet. Observation of unusual leaf spots on irrigated safflower cv. Centennial at Sidney, MT prompted this investigation of safflower as a potential alternate host of C. beticola. Safflower plants were inoculated with four isolates of C. beticola (C1, C2, Sid1, and Sid2) and incubated in growth chambers; leaf spot symptoms appeared between 3 and 4 weeks later. Polymerase chain reaction (PCR) amplification of extracts from lesion leaf tissue with C. beticola-specific primers produced fragments comparable with amplified fragments from purified cultures of control C. beticola. PCR assay of cultures of single spores from diseased safflower leaf lesions also produced fragments comparable with fragments from C. beticola cultures. Antibody that was raised from isolate C2 also bound to antigens from the single-spore cultures of the four C. beticola isolates. Inoculum from single-spore cultures from infected safflower also infected sugar beet and produced typical Cercospora leaf spot symptoms. Assay of these leaf lesions by PCR resulted in amplification of target fragments with the C. beticola-specific primers. Our results demonstrate that safflower is a new host of C. beticola.
TL;DR: Phylogenetic data obtained here support P. cladosporioides as closely related to other Pseudocercospora species that cluster within Mycosphaerella, suggesting that chemical control of this disease via a managed spraying programme may prove a viable option for controlling the disease in Spain.
TL;DR: Both, Ecolife® and the extract of rusted coffee leaves were significantly more effective in reducing the area under the lesion progress curve when applied at lower doses, indicating a possible effect on the induction of resistance.
Abstract: Phoma leaf spot, caused by Phoma costarricensis poses a serious threat to coffee (Coffea arabica) production, especially in the highlands of the state of Minas Gerais, Brazil. Extracts of citric biomass, coffee berry husks and coffee leaves severely affected by rust caused by Hemileia vastatrix, were evaluated against P. costarricensis. In an in vitro assay, aqueous extracts of rusted leaves and berry husks plus the commercial extracts based on citric biomass named Ecolife® and Agromil® were tested at various dilutions on the mycelial growth inhibition of P. costarricensis. In vivo, coffee seedlings maintained in glasshouse, were sprayed with these extracts seven days before inoculation of P. costarricensis. Only extracts from citric biomass had inhibitory effects on the fungus. In vivo, Ecolife® (5 ml/l), Agromil® (5 g/l) and the aqueous extract of rusted coffee leaves (dilution 1:6) reduced Phoma leaf spot. Both, Ecolife® and the extract of rusted coffee leaves were significantly more effective in reducing the area under the lesion progress curve when applied at lower doses, indicating a possible effect on the induction of resistance.
TL;DR: The results indicate that a mixture of Serenade and Cuprofix may be a useful addition to an integrated bacterial leaf spot disease management strategy but this treatment may be too variable to justify it as a stand-alone treatment.
Abstract: The efficacy of Serenade, Maneb, Cuprofix, and mixtures of these products were evaluated for efficacy in reducing disease incidence and severity of bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians in six trials at two locations between 2001 and 2003. Additionally, Messenger, elemental copper, Quadris, and Actigard were evaluated in at least two of these trials. Mixtures of Serenade and Cuprofix reduced disease incidence in three of six experiments and reduced disease severity in a fourth experiment. Treatment with the Maneb and Cuprofix mixture was less effective but resulted in significantly less disease and lower severity in single experiments. These results indicate that a mixture of Serenade and Cuprofix may be a useful addition to an integrated bacterial leaf spot disease management strategy but this treatment may be too variable to justify it as a stand-alone treatment.
TL;DR: The hypothesis that various pathogens are involved in PLS-like symptoms of maize and environmental conditions may influence the predominance of a specific agent is supported.
Abstract: This study aimed to identify and characterize the pathogens associated with symptoms similar to Phaeosphaeria leaf spot (PLS) of maize in different environmental conditions in Brazil. During the last decade, PLS became an important disease of maize in Brazil. However, doubt persists about the causal agent. Maize leaves with PLS-like lesions were collected from two locations (Cristalina, Goias State [GO] and Vila Maria, Rio Grande do Sul State [RS]) in two growing seasons. Fungi associated with leaf lesions were isolated and cultured for taxonomic identification. Pathogenicity tests were carried out and the results indicated that three fungi (a Phyllosticta sp., Phoma sorghina, and a Sporormiella sp.) caused leaf spot similar to PLS on maize. The composition of pathogenic fungi in PLS-like lesions varied depending on locations and growing seasons. The fungi P. sorghina and a Phoma sp. (Plenodomus section) occurred in all environments, but the Sporormiella and Phyllosticta spp. were restricted to G...
Dissertation•
01 Jan 2005
TL;DR: The in vitro screening of two biocontrol agents showed their antagonistic potential against C. canescens while, in vitro evaluation of fungicides revealed that Roko (Thiophanate methyl) completely inhibited the growth of pathogen at 5 ppm concentration followed by Bavistin (carbendaZim).
Abstract: The pulses, especially mungbean [Vigna radiata (L.) Wilczek] is an important crop grown extensively in India. Despite the multi facet importance the mungbean production could not be stabilized in the country. There are several constraints in mungbean production, among these diseases and particularly Cercospora leaf spot is most important fungal disease occurring regularly in mungbean growing areas. The disease is caused by Cercospora canescens Ellis and Martin. The disease appear during warm and humid weather leading to defoliation and low yield. Keeping in mind the importance of disease experiments were conducted to study the morphological and cultural characters of the pathogen and to find out the management strategies for the dlsease. The characteristic symptoms of Cercospora leaf spot were formation of leaf spot with brown to grayish centers and reddish borders, and Cercospora canescens was slow grow~ng fungus, having unbranched, septate, geniculate conidiophore, coming out of stomata in dense fascicles. Conidia were cylendric, hyaline, septate, straight or curved. Among the different culture media tested for growth and sporulation of pathogen Carrot Leaf Decoction Agar (CLDA) was found best, followed by Mungbean Leaf extract Oat meal Agar (MLOA), While studies conducted on effect of temperature revealed that Cercospora grew best at 30°C temperature, while no growth occurred at 5, 10 and 40°C. Maximum sporulation occurred at 25°C and no sporulation occurred at 5, 10,35 and 40°C temperatures. The in vitro screening of two biocontrol agents showed their antagonistic potential against C. canescens while, in vitro evaluation of fungicides revealed that Roko (Thiophanate methyl) completely inhibited the growth of pathogen at 5 ppm concentration followed by Bavistin (carbendaZim). Among plant extract neem and kaner extracts inhibited growth at 2 per cent dose resulted maximum inhibition. Seed treatment with Bavistin, T. harzianum + P. fluorescens and neem, eucalyptus and garlic extract were effective in enhancing gennination and increasing root and shoot length. Minimum disease severity, higher yield and thousand grain weight was observed in Roko spray plots while Bavistin Was next in order of efficacy. Among plant extracts neem and kaner were found most effective. Formulation of biocontrol agents did not showed .. much reduction in disease severity. The gennplasm line SML-668, ML-II09, ML-1165 and Co-5 showed resistant reaction against the disease. (H.S. Tripathi) Advisor ~p (Purva Saxena) Authoress
TL;DR: P. juliflora extract is identified as a significant component for the integrated management of groundnut foliar diseases and had no effect on the phenolic content of ground nut leaves both during LLS and rust infections.
Abstract: Late leaf spot (LLS, Phaeoisariopsis personata) and rust (Puccinia arachidis) are the two major biotic constraints of groundnut (Arachis hypogaea L.) of global importance. To identify economic and eco-friendly disease management options, we evaluated extracts of 38 plant spp. of 23 families, for their antifungal activity. Aqueous leaf extracts (20%, w/v) of Prosopis juliflora and Lycopersicon esculentum completely inhibited the in vitro germination of P. personata and P. arachidis, and extracts of Achras sapota, Cyamposis tetragonolobus, Piper betle and Tagetus patula were inhibitory by >95%. In the greenhouse, the severity of LLS and rust corresponded with the time interval between the foliar application of leaf extract and fungal inoculum. Extract of P. juliflora (2%, w/v) in simultaneous application reduced the lesion frequency of LLS and rust by ∼75%, and 35.7% and 50.7% in a prophylactic spray of 96 h before the pathogen inoculation. The extract had no effect on the phenolic content of groun...
TL;DR: This fungus has been reported previously on graminaceous genera such as Buchloe , Chloris , Oryza , Paspalum , Pennisetum , Sorghum , Triticum , Typha and Zea, but this is the first report on Cynodon.
Abstract: Curvularia leaf spot affects many species of grasses worldwide and is commonly caused by Curvularia eragrostidis , C. geniculata , C. intermedia , C. inaequalis , C. lunata , C. pallescens , C. protuberata or C. trifolii (Smith et al. , 1989). Weng et al. (1997) found that the most frequent disease of warm season grasses in southern China was caused by C. lunata , and C. affinis has been found on Festuca arundinacea (Huang et al. , 2004). There have been no other reports of curvularia leaf spot from central China. In August 2003, symptoms were observed in Wuhan, China, at a sports field on a Cynodon dactylon × C. transvaalensis hybrid. Yellow-brown spots of varying shape were formed on leaves and sheaths. The spots measured up to 1 cm in diameter: disease incidence was 5%. Isolations were made on acidified potato dextrose agar and after 2 days at 25 ° C, 8-mm-diameter cultures with appressed, white mycelium were observed. After 2 days more, the enlarging colonies acquired a greenish cast, which yielded spores of C. verruculosa (Ellis, 1966) with a rough-to-verrucose surface, three septa and an average size of 24·9 × 10·3 μ m. The two central cells were larger and darker than the terminal cells. Sequencing of the ITS region of ribosomal DNA showed a 99·6% match with a C. verruculosa sequence in GenBank. Pathogenicity was tested by inoculating field-grown plants. Ten stems, 12 cm long, were placed in Petri plates layered with moist tissue paper. Each stem was inoculated with two 5-mm-diameter mycelial plugs and the plates were incubated at 25 ° C, under continuous fluorescent light. The plugs were removed after 48 h, and within 24 h small spots appeared. Within 2 days after that, these spots had enlarged up to 1 cm in diameter, turning yellowbrown, with irregular shapes as seen in the field. No spots were seen on uninoculated stems. Isolations from spot margins, away from inoculated areas, yielded spores of C. verruculosa . This fungus has been reported previously on graminaceous genera such as Buchloe , Chloris , Oryza , Paspalum , Pennisetum , Sorghum , Triticum , Typha and Zea (Sivanesan, 1987), but this is the first report on Cynodon . The spores are similar in morphology to those of C. lunata except for the verrucose surface. Past diagnoses of curvularia leaf spot may have mistakenly identified C. verruculosa as C. lunata .
Journal Article•
Patent•
17 Feb 2005
TL;DR: In this paper, the present invention relates to agricultural insecticide and germicide and discloses substituted azole compounds, its preparation and application is represented as formula (I), the compounds of present invention have broad bactericidal activity and can be used to prevent and control various diseases of various crops.
Abstract: The present invention relates to agricultural insecticide and germicide and discloses substituted azole compounds, its preparation and application. The substituted azole compounds of the present invention is represented as formula (I). The compounds of present invention have broad bactericidal activity and can be used to prevent and control various diseases of various crops. For example they are excellent in control diseases such as downy mildew of cucumber, gray mold of cucumber, powdery mildew of cucumber, early blight of tomato, late blight of tomato, blight of capsicum, downy mildew of grape, white rot of grape, ring rot of apple, spot disease and leaf cast of apple, rice sheath blight disease, sheath and culm blight of rice, wheat rust, leaf spot of wheat, powdery mildew of wheat, rape sclerotium disease, spot disease of maize and so on. Some compounds have good insecticidal activity and acaricidal activity and can be used to control pests and acarids of various crops. For example they are used to control armyworm, little plutellid moth, aphids and lightish culex.
TL;DR: Five QTL on four different chromosomes were found to control PLS resistance in Mo17, in close agreement with the previous study, where generation mean analysis was used to study the inheritance of resistance to PLS.
Abstract: Carson, M. L., Stuber, C. W., and Senior, M. L. 2005. Quantitative trait loci conditioning resistance to Phaeosphaeria leaf spot of maize caused by Phaeosphaeria maydis. Plant Dis. 89:571574. Phaeosphaeria leaf spot (PLS) is a potentially important disease of maize (Zea mays) that has appeared in winter breeding nurseries in southern Florida. Inbred lines related to B73 are particularly susceptible to Phaeosphaeria leaf spot, whereas inbreds related to Mo17 are highly resistant. A previous study of the inheritance of resistance to Phaeosphaeria leaf spot in the cross B73 × Mo17 found that resistance is highly heritable and controlled by mostly additive gene action at three or four loci. In this study, we used 158 recombinant inbred (RI) lines derived from the cross B73 × Mo17 to map quantitative trait loci (QTL) governing resistance. The RI lines along with the parent inbred lines and the F1 were evaluated for PLS resistance in replicated trials over two winter growing seasons in southern Florida. Using the composite interval mapping (CIM) function of PLABQTL software, five QTL on four different chromosomes were found to control PLS resistance in Mo17. In addition, the additive × additive interaction between two of these QTL was found to be significant. Our results are in close agreement with the previous study, where generation mean analysis was used to study the inheritance of resistance to PLS.
TL;DR: Aqueous leaf extracts of Datura metel and Lawsonia inermis completely inhibited the germination of urediniospores of P. arachidis in vitro and integrated applications of D. metel extract and chlorothalonil may reduce the dependency on fungicides in groundnut cultivation.
Abstract: Late leaf spot (LLS) (causal agent Phaeoisariopsis personata) and rust (causal agent Puccinia arachidis) are economically important foliar diseases of groundnut (Arachis hypogaea) and have global significance. Aqueous leaf extracts of Datura metel and Lawsonia inermis, known for their high antifungal activity against P. personata, completely inhibited the germination of urediniospores of P. arachidis in vitro. In the greenhouse, extracts of D. metel (25g/L) and L. inermis (50g/L) applied as a prophylactic spray reduced the frequency of LLS lesions and rust pustules by 65–74% compared with controls. In field studies, a programme of four sprays of D. metel leaf extract at 45, 60, 75 and 90 days after sowing (DAS) was partially effective against the foliar diseases (LLS and rust) up to 95 DAS. A single spray of chlorothalonil at 45 DAS combined with three sprays of D. metel at 60, 75 and 90 DAS effectively reduced the combined severity of LLS and rust. The increase in pod yield by this treatment (91 % over control) was comparable with the sustained application of chlorothalonil. Further validation of integrated applications of D. metel extract and chlorothalonil may reduce the dependency on fungicides in groundnut cultivation.
01 Nov 2005
TL;DR: This is the first report of P. capsellae on B. juncea in Australia, an important disease of crucifers worldwide, and colonies showing purple-pink pigments in WA, and dark, compacted, and slow-growing colonies with a dentate margin on PDA.
Abstract: Brassica juncea (L.) Czern & Coss (mustard) has potential as a more drought-tolerant oilseed crop than the Brassica napus, and the first two canola-quality B. juncea cultivars will be sown as large strip trials across Australia in 2005. This will allow commercial evaluation of oil and meal quality and for seed multiplication for the commercial release Australia-wide in 2006. Inspection of experimental B. juncea field plantings at Beverley (32°6'30″S, 116°55'22″E), and Wongan Hills (30°50'32″S, 116°43'33″E), Western Australia in September 2004 indicated the occurrence of extensive leaf spotting during B. juncea flowering. Symptoms of this disease included as many as 15 or more grayish white-to-brownish spot lesions per leaf, often with a distinct brown margin. Some elongate grayish stem lesions were also observed as reported earlier for B. napus oilseed rape (1). When affected materials were incubated in moist chambers for 48 h, abundant conidia typical of Pseudocercosporella capsellae (Ellis & Everh.) Deighton were observed that matched the descriptions of conidia given by Deighton (2) and those on B. napus in Western Australia (1). Five single-spore cultures from lesions were grown on water agar (WA) where the colonies characteristically produced purple-pink pigment in the agar after 2 weeks growth in an incubator maintained at 20°C with a 12-h photoperiod (3). Since agar cultures of P. capsellae rarely produce conidia (3), this observation helped with the verification of the cultures. Mycelial inoculum from these cultures was used to inoculate cotyledons of 50 7-day-old plants of B. juncea to satisfy Koch's postulates. Small pieces of mycelia were teased out from the surface of the growing margin of potato dextrose agar (PDA) cultures and inoculated onto both lobes of each cotyledon and plants incubated in a 100% humidity chamber for 48 h within a controlled environment room maintained at 20/15°C (day/night) with a 12-h photoperiod. After 2 weeks, lesions 5 to 8 mm in diameter were observed on the cotyledons. There were no symptoms on control plants that were treated with water only. Lesions on infected cotyledons incubated on moist filter paper for 24 h produced abundant cylindrical conidia showing 2 to 3 septa measuring 42.9 to 71.4 μm long and 2.9 to 3.1 μm wide. Single-spore isolations from these conidia produced typical P. capsellae colonies showing purple-pink pigments in WA, and dark, compacted, and slow-growing colonies with a dentate margin on PDA. White leaf spot caused by P. capsellae is an important disease of crucifers worldwide, but to our knowledge, this is the first report of P. capsellae on B. juncea in Australia. In Western Australia, P. capsellae occurs on B. napus oilseed rape (1) and in 1956, 1984, and 1987, it was recorded on B. rapa, B. oleracea, and B. chinensis, respectively (4), and on the same range of Brassica hosts in other regions of Australia. References: (1) M. J. Barbetti and K. Sivasithamparam. Aust. Plant Pathol.10:43, 1981. (2) F. C. Deighton. Commonw. Mycol. Inst. Mycol. Pap. 133:42, 1973. (3) S. T. Koike. Plant Dis. 80:960, 1996. (4) R. G. Shivas. J. R. Soc. West. Aust. 72:1, 1989.
TL;DR: Significant differences between families with different staminate parents were found for blackspot, leaf spot and powdery mildew, indicating the possibility to select for resistance to these diseases in seedlings from crosses involving section Caninae in spite of the Canina meiosis.
Journal Article•
TL;DR: The high level of virulence variability in Phaeoisariopsis griseola, the causal agent of angular leaf spot of common bean, implies that multiple sources of resistance are required for effective management of the disease.
Abstract: A study was undertaken to characterise the virulence variability in Phaeoisariopsis griseola , the causal agent of
angular leaf spot of common bean ( Phaseolus vulgarisl/Ig L.) and to determine the physiological races of the pathogen
occurring in Kenya. Isolates of the pathogen were collected from farmers' fields in five districts representing the
diverse agroecological zones under which beans are produced in the country. Virulence variability of the isolates
was determined by their reactions in a set of 12 differential bean cultivars. One hundred isolates were characterised
into 44 physiological races, indicating great virulence variability in the pathogen. The races were grouped into three
virulence categories, namely Andean, Afro-Andean and Middle American. Fifty-five per cent of the races were
Middle American, 27% were Afro-Andean and 18%were Andean. Cluster analysis of the virulence data revealed a
53% similarity between Middle American isolates and Andean and Afro-Andean isolates, whereas Andean and
Afro-Andean isolates clustered together with no clear-cut separation. There was wide variation in virulence of
isolates collected from the same geographical location. Similarly, isolates obtained from the same bean cultivar,
either at the same or different locations, did not necessarily exhibit similar virulence patterns. There was a positive
correlation ( lIgrl/Ig = 0.519) between the virulence level of a race and its frequency of detection. Middle American races
were the most virulent and also the most widely distributed, whereas Andean and Afro-Andean races were more
rare and less virulent. Bean differential cultivar Mexico 54 showed high levels of resistance to 41 races of P. griseola
and is, therefore, a good source of resistance to angular leaf spot. However, the high level of virulence variability in
the angular leaf spot pathogen implies that multiple sources of resistance are required for effective management of
the disease.
TL;DR: To the authors' knowledge, this is the first report of E. persicina from common bean in Spain and in Europe, and microbiological characteristics were in agreement with the molecular identification of the isolates.
Abstract: A previously unreported leaf spot disease of common bean, which caused losses as much as 50% of the crops, was observed in southeastern Spain (Almeria, Granada, and Malaga provinces) in November 2003. In 2004, samples of cv. Donna with chlorotic and necrotic leaf spots were collected from Granada and processed for microbiological analysis. Bacteria isolated from the symptomatic leaves were determined to be fermentative on the basis of the ability to metabolize glucose in aerobic and anaerobic conditions. Three isolates were selected for pathogenicity tests. Bacterial suspensions (108 CFU/ml) were spray inoculated on bean seedlings (3 true leaves) of cv. Andecha. Beans were covered with transparent plastic bags for 2 days and held in an incubation chamber at 22°C and 80% relative humidity with a 12-h photoperiod. Assays were repeated at least twice. Symptoms that developed on plants inoculated with the three isolates were similar to those originally observed, while symptoms did not occur on control plants (inoculated with distilled water). The pathogenic isolates were identified by sequencing of the 16S rDNA after amplification (2). The amplified sequences were compared to available DNA sequences in databases by using BLAST (1); 99% homology with 16S rDNA of Erwinia persicina was shown. Microbiological characteristics (gram staining, motility, morphology, and results of biochemical tests) were in agreement with the molecular identification of the isolates. E. persicina has been isolated from bean in the United States (4) and described on tomato, banana, and cucumber in Japan (3). To our knowledge, this is the first report of E. persicina from common bean in Spain and in Europe. References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) U. Edwards et al. Nucleic Acids Res. 17:7843, 1989. (3) M. V. Hao et al. Int. J. Syst. Bacteriol. 40:379, 1990. (4) M. L. Schuster et al. Fitopatol. Bras. 6:345, 1981.