Showing papers on "Leaf spot published in 2004"
TL;DR: Rhizobacteria B101R, B212R, and A068R, selected as inducers of systemic resistance against Pseudomonas syringae pv.
224 citations
TL;DR: The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata, and the number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus.
Abstract: The causal agents of Alternaria brown spot of tangerines and tangerine hybrids, Alternaria leaf spot of rough lemon and Alternaria black rot of citrus historically have been referred to as Alternaria citri or A. alternata. Ten species of Alternaria recently were described among a set of isolates from leaf lesions on rough lemon (Citrus jambhiri) and tangelo (C. paradisi × C. reticulata), and none of these isolates was considered representative of A. alternata or A. citri. To test the hypothesis that these newly described morphological species are congruent with phylogenetic species, selected Alternaria brown spot and leaf spot isolates, citrus black rot isolates (post-harvest pathogens), isolates associated with healthy citrus tissue and reference species of Alternaria from noncitrus hosts were scored for sequence variation at five genomic regions and used to estimate phylogenies. These data included 432 bp from the 5' end of the mitochondrial ribosomal large subunit (mtLSU), 365 bp from the 5' end of the beta-tubulin gene, 464 bp of an endopolygalacturonase gene (endoPG) and 559 and 571 bp, respectively, of two anonymous genomic regions (OPA1-3 and OPA2-1). The mtLSU and beta-tubulin phylogenies clearly differentiated A. limicola, a large-spored species causing leaf spot of Mexican lime, from the small-spored isolates associated with citrus but were insufficiently variable to resolve evolutionary relationships among the small-spored isolates from citrus and other hosts. Sequence analysis of translation elongation factor alpha, calmodulin, actin, chitin synthase and 1, 3, 8-trihydroxynaphthalene reductase genes similarly failed to uncover significant variation among the small-spored isolates. Phylogenies estimated independently from endoPG, OPA1-3 and OPA2-1 data were congruent, and analysis of the combined data from these regions revealed nine clades, eight of which contained small-spored, citrus-associated isolates. Lineages inferred from analysis of the combined dataset were in general agreement with described morphospecies, however, three clades contained more than one morphological species and one morphospecies (A. citrimacularis) was polyphyletic. Citrus black rot isolates also were found to be members of more than a single lineage. The number of morphospecies associated with citrus exceeded that which could be supported under a phylogenetic species concept, and isolates in only five of nine phylogenetic lineages consistently were correlated with a specific host, disease or ecological niche on citrus. We advocate collapsing all small-spored, citrus-associated isolates of Alternaria into a single phylogenetic species, A. alternata.
183 citations
TL;DR: Fungicides in the benzimidazole and triazole class as well as organotin derivatives and strobilurins have successfully been used to control Cercospora leaf spot.
Abstract: SUMMARY
Leaf spot disease caused by Cercospora beticola Sacc. is the most destructive foliar pathogen of sugarbeet worldwide. In addition to reducing yield and quality of sugarbeet, the control of leaf spot disease by extensive fungicide application incurs added costs to producers and repeatedly has selected for fungicide-tolerant C. beticola strains. The genetics and biochemistry of virulence have been examined less for C. beticola as compared with the related fungi C. nicotianae, C. kikuchii and C. zeae-maydis, fungi to which the physiology of C. beticola is often compared. C. beticola populations generally are not characterized as having race structure, although a case of race-specific resistance in sugarbeet to C. beticola has been reported. Resistance currently implemented in the field is quantitatively inherited and exhibits low to medium heritability.
Taxonomy: Cercospora beticola Sacc.; Kingdom Fungi, Subdivision Deuteromycetes, Class Hyphomycetes, Order Hyphales, Genus Cercospora.
Identification: Circular, brown to red delimited spots with ashen-grey centre, 0.5–6 mm diameter; dark brown to black stromata against grey background; pale brown unbranched sparingly septate conidiophores, hyaline acicular conidia, multiseptate, from 2.5 to 4 µm wide and 50–200 µm long.
Host range: Propagative on Beta vulgaris and most species of Beta. Reported on members of the Chenopodiaceae and on Amaranthus.
Disease symptoms: Infected leaves and petioles of B. vulgaris exhibit numerous circular leaf spots that coalesce in severe cases causing complete leaf collapse. Dark specks within a grey spot centre are characteristic for the disease. Older leaves exhibit a greater number of lesions with larger spot diameter. During the latter stage of severe epiphytotics, new leaf growth can be seen emerging from the plant surrounded by prostrate, collapsed leaves.
Control: Fungicides in the benzimidazole and triazole class as well as organotin derivatives and strobilurins have successfully been used to control Cercospora leaf spot. Elevated levels of tolerance in populations of C. beticola to some of the chemicals registered for control has been documented. Partial genetic resistance also is used to reduce leaf spot disease.
140 citations
TL;DR: The results demonstrate that combined rhizobacterial and chemical treatments in the field may permit reducing fungicidal spraying frequency while at the same time increasing crop yields.
Abstract: The ability of a rhizobacterium to protect tomato plants against naturally occurring diseases as well as to improve crop yield under field conditions was studied. The rhizobacterium was introduced to the plants through seed microbiolization. Treatments consisted of different frequencies of fungicide (Chlorothalonyl) sprayings (5, 10 or 20 applications) of tomato plants grown from either microbiolized or non-microbiolized seeds over a 90-day evaluation period. Treatment of non-microbiolized seeds without fungicide application was included as a control. The progress of the following three naturally occurring diseases was evaluated in the field and quantified: early blight (Alternaria solani), late blight (Phytophthora infestans), and septoria leaf spot (Septoria lycopersici). All treatments resulted in reduced disease severity when compared with the control treatment. Highest final fruit yields were found after treatment of plants grown from non-microbiolized seeds and sprayed with fungicide 20 times over 90 days, and for treatment of plants from microbiolized seeds that received 10 fungicide spray applications, although all treatments increased yield over that obtained in the control treatment. The results demonstrate that combined rhizobacterial and chemical treatments in the field may permit reducing fungicidal spraying frequency while at the same time increasing crop yields.
65 citations
TL;DR: Leaf photosynthesis was strongly and negatively correlated with leaf spot severity in both hybrids, and β-values indicated that photosynthetic impairment extended beyond visibly damaged leaf tissue, however, large differences in β between hybrids indicated differential photosynthesis consequences for a given leaf Spot severity.
Abstract: Summary • In foliage of two hybrid poplars, clone DN-34 ( Populus deltoides × P. nigra ) and clone NM-6 ( P. nigra × P. maximowiczii ), we examined relationships between photosynthesis and severity of leaf spot induced by Marssonina brunnea f. sp. brunnea , a common disease of many tree species in the Populus genus with the potential to affect growth. • Gas exchange was measured on asymptomatic and diseased foliage in monoculture stands of each clone. The equation Y = (1 ‐ x ) β was used to characterize the relationship between relative photosynthesis ( Y ) and percent leaf spot ( x ), where β represents the ratio between functional impairment and measured lesion area. • Leaf photosynthesis was strongly and negatively correlated with leaf spot severity in both hybrids, and β -values indicated that photosynthetic impairment extended beyond visibly damaged leaf tissue. However, large differences in β between hybrids indicated differential photosynthetic consequences for a given leaf spot severity. For each hybrid, values of β were positively related to photosynthetic photon flux density incident upon the leaf during gas exchange measurement. • Declines in leaf photosynthesis appeared to result from a disruption of the photosynthetic apparatus by the invading pathogen. However, specific causes for the differential photosynthetic responses of the two hybrids to disease remained elusive.
55 citations
TL;DR: The number of fungicide applications could be reduced without compromising control of leaf spot when reduced tillage is used, especially if combined with moderately resistant cultivars.
Abstract: Field experiments were conducted in 2000 and 2001 on Georgia Green, Florida MDR-98, and C-99R peanut (Arachis hypogaea) cultivars in Tifton, GA, to determine the effects of tillage practices on early leaf spot (Cercospora arachidicola) epidemics under standard fungicide regimes and fungicide regimes with fewer applications. Leaf spot epidemics were suppressed in reduced tillage (strip-till) plots compared with conventional tillage plots and were suppressed in MDR-98 and C-99R cultivars compared with the standard runner-type cultivar, Georgia Green. Within tillage and cultivar combinations, leaf spot intensity typically was lower in plots treated with fungicides at standard intervals (seven total applications) than in those treated at extended intervals (four total applications). However, in most cases, leaf spot control in extended interval treatments in the strip-till system was comparable to that in the standard interval treatments in conventional tillage. Based on these results, the number of fungicide applications could be reduced without compromising control of leaf spot when reduced tillage is used, especially if combined with moderately resistant cultivars. Suppression of leaf spot epidemics in the strip-till plots did not coincide with higher yields in either year. In 2001, yields were lower in strip-till plots than in conventional tillage plots. Yields were typically higher in the cultivar C-99R than in Georgia Green, regardless of the tillage treatment.
49 citations
TL;DR: Adequate carbohydrate supply during the fall is critical for optimal flower bud set in blueberry; therefore, these results document the potential for marked yield losses due to biotic and abiotic leaf spots.
Abstract: Leaf spots caused by fungal pathogens or abiotic factors can be prevalent on southern blueberries after harvest during the summer and fall, yet little is known about how they affect physio...
49 citations
TL;DR: Results indicate that risk for leaf spot disease on barley would be lower following wheat, crambe, canola and dry pea compared with the barley-after-barley treatment, and wheat yields were similar across all treatments one year, but differences were detected in another year with the wheat- after-wheat treatment having the lowest yield.
Abstract: Crop diversification and crop sequencing can influence plant disease risk in cropping systems. The objective of this research was to determine the effect of 10 previous crops on leaf spot diseases of barley (Hordeum vulgare L.) and hard red spring wheat (Triticum aestivum L.). Barley and spring wheat were direct-seeded (no till) in the crop residue of 10 crops {barley, canola (Brassica napus L.), crambe (Crambe abyssinica Hochst. ex R.E. Fr.), dry bean (Phaseolus vulgaris L.), dry pea (Pisum sativum L.), flax (Linum usitatissimum L.), safflower (Carthamus tinctorius L.), soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), and spring wheat). Barley was evaluated for leaf spot diseases 15 times over 2 yr. Results indicate that risk for leaf spot disease on barley would be lower following wheat, crambe, canola and dry pea compared with the barley-after-barley treatment. Although barley yields were similar across all treatments one year, differences were detected in another year with the barley-after-barley treatment having the lowest yield. Spring wheat was evaluated for leaf spot diseases 22 times over 2 yr. Differences among treatments were more detectable in earlier evaluations, indicating a greater influence of crop residue and carryover of inoculum early in the season compared with later. The risk for leaf spot disease was lower when wheat was grown after canola, barley, crambe, and flax than when grown after the other crops. Although wheat yields were similar across all treatments one year, differences were detected in another year with the wheat-after-wheat treatment having the lowest yield.
45 citations
TL;DR: B. oryzae, a common pathogen on rice (Oryza sativa), is reported to cause a disease on switch grass for the first time, and has the potential to diminish yields of switch grass under intensive plantings for high biomass production.
Abstract: Switch grass (Panicum virgatum) is a native, perennial warm-season grass used for hay, summer grazing, soil conservation, and wildlife habitat. It is also being developed as a biomass crop for renewable energy. A previously unreported leaf-spot disease on switch grass was observed in North Dakota plantings. From 1999 to 2002, a fungus was consistently isolated from leaf spots on switch grass. It was identified as Bipolaris oryzae (teleomorph: Cochliobolus miyabeanus). Conidial morphology agreed with that of B. oryzae, and comparison of DNA sequences from glyceraldehyde-3-phosphate dehydrogenase also indicated that the isolates were B. oryzae. Greenhouse pathogenicity tests confirmed the ability of B. oryzae to cause symptoms of leaf spot on switch grass. This is the first time that B. oryzae, a common pathogen on rice (Oryza sativa), is reported to cause a disease on switch grass. This pathogen has the potential to diminish yields of switch grass under intensive plantings for high biomass production, part...
35 citations
TL;DR: High broad-sense heritability estimate and similar response of progeny compared to selected parents indicated that parent selection based on progeny tests was a good selection method to predict the combining ability of the parents and proved successful in improving gray leaf spot resistance in the next generation.
Abstract: Gray leaf spot, caused by the fungus Pyricularia grisea (Cooke) Sacc. [teleomorph Magnaporthe grisea (T.T. Herbert) Yaegashi & Udagawa], can be a devastating disease on perennial ryegrass (Lolium perenne L.). The identification and utilization of perennial ryegrass cultivars with improved resistance to gray leaf spot would reduce the need for fungicide applications. The objectives of this study were to: (i) evaluate cultivars, experimental selections, and single-plot progenies of perennial ryegrass for resistance to gray leaf spot, (ii) develop populations from selected resistant parents to determine improvements in the next generation, and (iii) determine heritability and the response to selection for gray leaf spot resistance in perennial ryegrass populations. Two perennial ryegrass field experiments consisting of commercial cultivars and experimental selections, were established in 2000 and 2001 at Adelphia, NJ. Susceptibility of germplasm to gray leaf spot was evaluated following ephemeral natural outbreaks of the disease that occurred three to four weeks post seeding. Parents with improved resistance to gray leaf spot were selected based on progeny turf plot evaluations in 2000, inter-pollinated and seeded into turf plots in the 2001 experiment. Most cultivars and selections evaluated in both experiments had greater than 50% gray leaf spot disease. The high broad-sense heritability estimate (0.92) and similar response of progeny compared to selected parents indicated that parent selection based on progeny tests was a good selection method to predict the combining ability of the parents. It also proved successful in improving gray leaf spot resistance in the next generation, which will be important for the development of more disease resistant cultivars.
34 citations
TL;DR: From molecular analysis it was found that although cultivated A. hypogaea is made up of A and B genomes, A. kempff-mercadoi may not be as closely related to it as are some of the other A genome species.
Abstract: Arachis kempff-mercadoi is a wild species from the section Arachis. All kempff-mercadoi accessions originate from the Santa Cruz province of Bolivia and they represent Arachis species with the A genome. From molecular analysis it was found that although cultivated A. hypogaea is made up of A and B genomes, A. kempff-mercadoi may not be as closely related to it as are some of the other A genome species. Arachis kempff-mercadoi is of interest because it has multiple disease resistance. It was crossed with a Spanish A. hypogaea cultivar which is susceptible to foliar diseases and to the insect pest Spodoptera litura. The success rate of the cross A. hypogaea (2n = 40) x A. kempff-mercadoi (2n = 20) was very low, but it could be increased by culturing immature seeds in vitro. Although the hybrids were triploids. a few fertile pollen grains were obtained due to the formation of restitution nuclei in the F 1 plants. Interspecific derivatives at the BC 2 F 2 generation were scored for early leaf spot, late leaf spot and to Spodoptera damage. Screening results showed that 29% of the derivatives had both early and late leaf spot resistance and that less than 5% of the derivatives had resistance to both the foliar diseases and to Spodoptera.
TL;DR: The current study diagnosed the disease as gray leaf spot caused by Stemphylium solani Weber and S. lycopersici (Enjoji) Yamamoto, both of which are pathogenic in pepper and tomato plants.
Abstract: A disease causing severe leaf spots in pepper plants has been observed in northern Gyeongbuk and Gangwon provinces in Korea since 1994. The current study diagnosed the disease as gray leaf spot caused by Stemphylium solani Weber and S. lycopersici (Enjoji) Yamamoto, both of which are pathogenic in pepper and tomato plants. Although the disease has been found in almost all areas where peppers are grown, it is more severe in mountain terrains where the nights are cool. Both species of pathogenic fungi were found to sporu-late profusely on V-8 juice agar in plastic or Pyrex glass Petri dishes, although not in domestically-produced glass Petri dishes, when cultured at under irradi-ation from a daylight fluorescent lamp with a 12-hour light and dark alternation. The domestically-produced glass Petri dishes, which are made of window glass, were found to block near ultraviolet wavelengths, around and below 300 nm, which explained why the fungi did not sporulate. However, sporulation decreased at above and most isolates failed to sporulate above . The worst level of disease was obtained when the inoculated plants were incubated with a night and day temperature regime relative to 4 night/day temperature combinations (15/20, 20/25, 25/30, and 30/35).
TL;DR: Differences in frequencies among the different morphological types found within the three orchards remained relatively similar throughout the season and from year to year, suggesting that the relative frequencies of G. cingulata, C. gloeosporioides, and C. acutatum remain stable in an orchard once the fungi are established.
Abstract: The population diversity within isolates of Glomerella cingulata and Colletotrichum spp. associated with Glomerella leaf spot and bitter rot of apples was studied in an orchard of cv. Granny Smith located in Wilkes County, NC, and one orchard each of cultivars Granny Smith and Gala located in Lincoln County, NC. Morphological characters and vegetative compatibility groups (VCGs) were used to determine diversity within the species. The relative frequencies of the morphological types found within each species in each orchard were also determined. G. cingulata was the predominant species associated with bitter rot in the three orchards and Glomerella leaf spot in the Gala orchard. In the three orchards, different morphological types were observed within isolates of G. cingulata and Colletotrichum acutatum, but not within isolates of Colletotrichum gloeosporioides. Isolates of C. gloeosporioides were not found in the orchard of cv. Granny Smith in Lincoln County. In the other two orchards, C. gloeosporioides represented the lowest proportion of the population. Three VCGs were found among isolates of G. cingulata (VCG-1, 2, and 6), two among isolates of C. gloeosporioides (VCG-9 and 10), and two among isolates of C. acutatum (VCG-15 and 16). VCGs 2, 6, 9, 10, 15, and 16 were found in the Granny Smith orchard in Wilkes County, VCGs 1, 2, and 6 in the Gala orchard in Lincoln County, and VCGs 2 and 6 in the Granny Smith orchard in Lincoln County. Differences in frequencies among the different morphological types found within the three orchards remained relatively similar throughout the season and from year to year, suggesting that the relative frequencies of G. cingulata, C. gloeosporioides, and C. acutatum remain stable in an orchard once the fungi are established.
Journal Article•
TL;DR: The results obtained suggest that B. cepacia may be considered for use as an antagonist for the biocontrol of the soil fungi which attack peppers.
TL;DR: Investigation of the effect of Mo application in conjunction with variably applied fungicide on common bean in the management of angular leaf spot found that fungicide spray applied once or twice in the bean flowering period (25-45 DAS) should provide substantial control of ALS.
Abstract: The yield of common bean (Phaseolus vulgaris L.) is affected by several factors, including diseases such as angular leaf spot (Phaeoisariopsis griseola) and N deficiency caused by lack of nodulation. In Minas Gerais State, Brazil, farmers have been using both fungicide and molybdenum (Mo) applications to improve crop yield. The objective of this research was to investigate the effect of Mo application in conjunction with variably applied fungicide on common bean in the management of angular leaf spot (ALS). Field experiments were conducted in two seasons, wet and dry, with eight fungicide treatment schedules, with and without Mo. Angular leaf spot severity, plant growth, photosynthesis, and yield were measured. A single application of Mo 25 d after sowing (DAS) decreased the area under the disease progress curve by 38% and increased the area under the leaf area progress curve by 20%, leaf photosynthesis by 26%, and yield by 51%. When combined with the Mo applications, fungicide spray applied once (at an early growth stage) or twice in the bean flowering period (25-45 DAS) should provide substantial control of ALS.
TL;DR: The results suggest that the current grey leaf spot epidemics in East Africa are due to favourable cultivars, poor mineral nutrition and environmental interactions.
Abstract: Grey leaf spot incited by Cercospora zeae-maydis is a new devastating foliar disease of maize in East Africa. For effective control, elucidation of the most critical elements of the grey leaf spot disease pyramid is important. This study investigated the role of mineral nutrition, pathogen variability and host resistance in the epidemic. Trials were conducted under field and controlled environments. The 28 isolates used in the controlled environment varied significantly (P ≤ 0.05) in parasitic fitness measured indirectly as disease efficiency, but no infection pattern could be attributed to known C. zeae-maydis pathotypes. Data from field trials showed that host resistance and mineral nutrition significantly (P ≤ 0.05) affected disease efficiency, with highest disease development occurring in nitrogen-augmented plots. Exclusive phosphorus application had no clear effect on grey leaf spot epidemics but combined application with nitrogen significantly (P ≤ 0.05) reduced the predisposition effects of nitrogen to the disease. Overall, treated plots had less disease than unfertilised plots. Fertiliser application had no effect on sporulation capacity, while cultivars significantly affected it. Geographic differences in amount of disease were observed, suggesting environment influences on grey leaf spot incidence. The results suggest that the current grey leaf spot epidemics in East Africa are due to favourable cultivars, poor mineral nutrition and environmental interactions.
01 Jan 2004
TL;DR: Data from surveys of winter oilseed rape crops in England and Wales in growing seasons with harvests in 1987–99 were used to construct statistical models to predict, in autumn (October), the incidence of light leaf spot caused by Pyrenopeziza brassicae, at both regional and individual crop scales.
Abstract: Data from surveys of winter oilseed rape crops in England and Wales in growing seasons with harvests in 1987–99 were used to construct statistical models to predict, in autumn (October), the incidence of light leaf spot caused by Pyrenopeziza brassicae on winter oilseed rape crops the following spring (March/April), at both regional and individual crop scales. Regions (groups of counties) with similar seasonal patterns of incidence (percentage of plants affected) of light leaf spot were defined by using principal coordinates analysis on the survey data. At the regional scale, explanatory variables for the statistical models were regional weather (mean summer temperature and mean monthly winter rainfall) and survey data for regional light leaf spot incidence (percentage of plants with affected pods) in July of the previous season. At the crop scale, further explanatory variables were crop cultivar (light leaf spot resistance rating), sowing date (number of weeks before/after 1 September), autumn fungicide use and light leaf spot incidence in autumn. Risk of severe light leaf spot (> 25% plants affected) in a crop in spring was also predicted, and uncertainty in predictions was assessed. The models were validated using data from spring surveys of winter oilseed rape crops in England and Wales from 2000 to 2003, and reasons for uncertainty in predictions for individual crops are discussed.
Journal Article•
TL;DR: Screening for disease resistance against three major diseases of cabbage, cauliflower and cauliflower using partially purified toxic fractions and cell free culture filtrate and field evaluation by artificial inoculation methods are reported.
Abstract: Success of any breeding programme for disease resistance largely depends on the availability of resistant sources, and reliable screening techniques against pathogens. Screening for disease resistance against three major diseases of cabbage (Barassica oleracea var. capitata) and cauliflower (B. oleracea var. botrytis) namely i.e. Sclerotinia rot (Sclerotinia sclerotiorum), Alternaria leaf spot (Alternaria brassicicola) and black rot (Xanthomonas campestris pv.campestris) under laboratory conditions with detached leaf technique using partially purified toxic fractions and cell free culture filtrate and field evaluation by artificial inoculation methods are reported here.
TL;DR: In this article, a variant of the energy budget model was developed to model leaf wetness duration for use in forecasting the oilseed diseases, stem canker and light leaf spot.
TL;DR: This report is the first on isolates of the causal fungus that are highly resistant to both T and D and the second report on isolate resistant to A.
Abstract: Sensitivity of Corynespora cassicola, causal agent of Corynespora leaf spot of cucumber, isolated from cucumber plants in Okayama Prefecture to thiophanate-methyl (T) and diethofencarb (D), and azoxystrobin (A) was investigated using the minimum inhibitory concentration (MIC) method and a bioassay. With the MIC method, 29 isolates among 193 isolates were highly resistant to both T and D. In the bioassay test, an isolate resistant to A was isolated from cucumber plants in a field. This report is the first on isolates of the causal fungus that are highly resistant to both T and D and the second report on isolates resistant to A.
TL;DR: Eggplant is a hardy annual herbaceous plant that is attacked by many insect pests and diseases and some varieties tolerant/resistant to different biotic and abiotic stresses are developed.
Abstract: Summary Eggplant or brinjal is an important crop of many countries. It is highly productive crop and consumed as a cooked vegetable in various ways. It is a hardy annual herbaceous plant. There is a lot of variability exists in the nature in color, shape, size, etc. A number of cultivars are grown across the globe depending on the market needs and consumer preference. Different worker in terms of yield, maturity, uniform harvest, etc., has showed considerable amount of heterosis. Eggplant is attacked by many insect pests and diseases like Shoot and fruit borer, Epilachna beetle, Damping off, Phomopsis blight, Leaf spot, Wilt, Little leaf, Fruit rot, Collar rot, etc. Some varieties tolerant/resistant to different biotic and abiotic stresses are developed. Further work on resistance breeding is of much importance in this regard. Hybrids are also popular in this crop. In some countries, F2 are also being marketed by different companies. The flowers of eggplant are large and showy with the corolla purple in c...
Journal Article•
TL;DR: Results of this study suggest that multiple disease resistance in dogwoods may be achieved through crosses between C. kousa and C. florida.
Abstract: Disease resistance in several Cornus species and cultivars to three foliar pathogens was evaluated in a 5-year study. Of the 51 accessions evaluated, 20 were of C. kousa, 21 of C. florida, two of C. sericea, two of C. mas, one of C. alternifolia, and five were interspe- cific hybrids of C. kousa × C. florida. Powdery mildew and spot anthracnose caused by Erysiphe (sect. Microsphaera) pulchra, and Elsinoe corni, respectively, were the most prevalent and severe diseases. Eighteen cultivars of C. kousa, one of C. mas, two of C. sericea, one of C. alternifolia, and four interspecific hybrids were highly resistant to powdery mildew, while 19 C. florida cultivars were susceptible, of which two were moderately resistant. Spot anthracnose was the second most prevalent disease, but its severity was generally low. Three C. kousa cultivars, ten of C. florida, and one of C. mas were mildly susceptible to spot anthracnose. Both cultivars of C. sericea were highly susceptible to Septoria leaf spot (Septoria cornicola), and heavy infections were observed throughout the study. Most C. florida cultivars were highly susceptible to powdery mildew, while most C. kousa cultivars were highly resistant. Results of this study suggest that multiple disease resistance in dogwoods may be achieved through crosses between C. kousa and C. florida.
TL;DR: The investigation on the circular leaf spot pathogenic, Mycosphaerella nawae, related to disease outbreak such as overwintering of pathogen, inoculum formation and spread, incubation period after infection, and secondary inoculum is described and summarized.
Abstract: The circular leaf spot of persimmon is occurred almost every place where persimmon is cultivated, especially the disease outbreak severely in southern part of Korea. The disease reveals unusually long incubation period after pathogen invade into leaf tissue and no practical control measure is available once the symptom has appeared. Most of the farmers just follow the suggested spray schedules calculated on the basis of weather condition of ordinary years. Therefore the damages due to circular leaf spot greatly differ year after year. In this article, we tried to describe and summarized the investigation on the circular leaf spot pathogen, Mycosphaerella nawae, related to disease outbreak such as overwintering of pathogen, inoculum formation and spread, incubation period after infection, and secondary inoculum. With the summary of these results, we suggest the disease cycle of circular leaf spot of persimmon. The pathogen overwinters in diseased leaves as mycelial form or pseudoperithecial premodium. The pseudoperitheria become matured in spring as the temperature raise and forms asci and ascospores. The maturation of pseudoperithecia are closely related to the temperatures during March and early April. The ascospores completely mature in early May and the ascospores released when the pseudoperithecia absorbed enough moisture after rainfall. The release of ascospores are diverse greatly with the variation of maturity of pseudoperithecia. Generally the spore start to release from middle of May to early of July. Duration of ascospore release is depend on the weather condition of particular year, especially amount and number of precipitation. The ascospores produced from pseudoperithecia is known to the only inoculum for circular leaf spot disease. But according to the results obtained from our investigations, the conidia formed on the lesions which incited by natural infection. This conidia are infectious to persimmon leaves and formed identical symptom as natural infection. The time of producing secondary inoculum of circular leaf spot of persimmon is considered too late to develop new disease. Generally the importance of secondary inoculum is low but the conidia produced in early September are competent to develop new disease and new infection also significantly affect to harvest of persimmon. The importance of circular leaf spot disease is recognized well to farmers. The approaches to control of the disease should be initiated on the basis of the knowledges of inoculum dynamics and ecology of disease development. The forecasting system for circular leaf spot is need to be developed.
TL;DR: To create genetic variability in cultivated sunflower and to select lines resistant to Alternaria leaf spot, sunflower seeds of the genotype HA BR 104 were irradiated with 150 and 165 Gy of gamma rays and the best lines will be used for hybrid production.
Abstract: SUMMARY Genetic variability for resistance to Alternaria leaf spot disease (Alternaria helianthi) can be induced by radiation or chemical mutagens. The objectives of this study were to create genetic variability in cultivated sunflower and to select lines resistant to Alternaria leaf spot. In the first experiment, sunflower seeds of the genotype HA BR 104 were irradiated with 150 and 165 Gy of gamma rays. Seeds were sown in the field at the Embrapa Soybean experimental station, in Londrina, PR, Brazil and M1 plants were harvested in bulk. M2 ,M3 and M4 plants were screened for disease resistance under natural infection in the field. Plants were evaluated for Alternaria leaf spot symptoms, using a diagrammatic scale from 0 (no symptoms) to 5 (maximum infection). Before flowering, plants showing no symptoms of Alternaria leaf spot (grade 0) or less than 5% diseased leaf area (grade 1) were bagged for self-pollination. Self-pollinated plants and open-pollinated plants from 150 Gy and 165 Gy populations with no or mild disease symptoms were selected. In the second experiment, sunflower seeds of the genotypes HA 300 and HA BR 104 were treated with ethyl methanesulfonate (EMS) at 0.015 mol dm -3 . Selected M2 and M3 were screened for disease resistance in the field. From the EMS treatment, 300 M3 plants with no disease were recovered. All these lines will be tested for combining ability. The best lines will be used for hybrid production.
01 Jan 2004
TL;DR: In this article, a study was conducted at Bako Agricultural Research Center for three years (1999-2001) to quantify the levels of yield loss in maize (Zea mays L.) incurred by grey leaf spot (GLS) disease caused by Cercospora zeae-maydis.
Abstract: A study was conducted at Bako Agricultural Research Center for three years (1999-2001) to quantify the levels of yield loss in maize (Zea mays L.) incurred by grey leaf spot (GLS) disease caused by Cercospora zeae-maydis. Three commercial varieties with different levels of resistance to GLS, namely, Bh-660 (resistant), BH-140 (moderately resistant) and Phb-3253 (susceptible) and three treatments (inoculated, fungicide sprayed and unsprayed control) were used in factorial combination with three replications. Significant differences were observed among varieties for percent infected plants per plot in all three years and for percent infected leaves per infected plant in 1999 and 2001. The main effect of treatment was also significant for disease severity in all years. Variety x treatment interaction was significant for percent upper ear leaf area infected in 1999, and for AUDPC and upper ear leaf area infected in 2000 and 2001. The main effect of year was significant for thousand-kernel weight and ear diameter. Varietal effect was significant for thousand-kernel weight and grain yield, while treatment effect was significant for ear diameter and grain yield. The interactions among year, variety and treatment were non-significant. Mean kernel and grain yield losses ranged from 1.7 to 10.0% and 7.8 to 29.1%, respectively, on different varieties. Grain yield losses in varieties BH-660, BH-140 and Phb-3253 ranged 0-14.9, 13.7-18.3, and 20.8-36.9%, respectively, during the three years. The effect of GLS on ear length and diameter, particularly under natural (unsprayed) condition was not significant. The result indicated that GLS could be severe in some favourable seasons causing significant yield losses even or resistant varieties.
TL;DR: There were significant high correlations between disease severity score, pod and haulm yields, and the mixture of benomyl and mancozeb gave significantly better control of the leaf spots and higher yield than the others.
Abstract: Trials were conducted at the Institute for Agricultural Research (IAR) farm, Samaru (Lat. 11° 11′N, Long. 07° 35′E) in 1999 and 2000 cropping seasons to evaluate cheap biorational products for the control of late leaf spots on groundnut. SAMNUT – 14(Ex – Dakar) a variety which is susceptible to leaf spots but commonly grown by resource-poor farmers was used for the study. The experimental design was a randomized complete block in which there were five treatments, neem (Azadirachta indica) seed extract, black soap and cow dung as biorational products, the recommended mixture of benomyl (Benlate 50% wp Du Pont) plus mancozeb (Dithane M-45) and an unsprayed check. Each plot consisted of five 75 cm ridges 5 m long and there were three replicates. The mixture of benomyl and mancozeb gave significantly better control of the leaf spots and higher yield than the others. Neem seed extract and black soap were not significantly different from each other in the disease control but different from cow dung extract whic...
TL;DR: Diaporthe perjuncta appears to be an endophyte, rather than a pathogen of grapevine, which is associated with Phomopsis cane and leaf spot of Grapevine.
Abstract: In Australia, Diaporthe perjuncta (formerly known as Phomopsis taxon 1) and Phomopsis viticola (Phomopsis taxon 2) have been associated with Phomopsis cane and leaf spot of grapevine. Although P. viticola causes distinct leaf spots, as well as lesions on shoots and canes, the pathogenicity of D. perjuncta is relatively unknown. The pathogenicity of D. perjuncta and P. viticola was studied in relation to symptom expression and bud loss. Only P. viticola caused brown-black, longitudinal, necrotic lesions on stem tissue and leaf spots characteristic of the disease, whereas both D. perjuncta and P. viticola induced bleaching of dormant canes. Inoculation of dormant buds with D. perjuncta did not cause bud death. D. perjuncta and P. viticola were reisolated from inoculated tissue and into pure culture. D. perjuncta colonized the epidermis and cortex of the grapevine shoot but not the vascular tissue. D. perjuncta appears to be an endophyte, rather than a pathogen of grapevine.