Evaluation of sunflower genotypes for Alternaria disease resistance to identify the resistant genotypes
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Alternaria leaf spot caused by Alternaria helianthi has been considered as economically important disease. The present study was carried out to identify resistant or moderately resistant genotypes against the Alternaria leaf spot in field screening and artificial screening. Out of 115 genotypes screened in field 31 genotypes were moderately resistant, 60 genotypes were susceptible whereas 24 genotypes were highly susceptible. Resistance to Alternaria is reported to exhibit differential reactions with the environment, hence field screening alone is insufficient while choosing genotypes for further resistance breeding programme. Therefore genotypes which showed moderate resistance (31) and high susceptibility (24) were screened artificially, along with 4 checks. Moderate resistant reaction for Alternaria leaf blight disease was observed in 1B, COSF 7B, CSFI 5083, CSFI 5181, CSFI 5213, CSFI 5276, CSFI 5292, CSFI 5336, POP 449-1-2-4, CSFI 13034, CSFI 13043 and TNHSF 239-68-1-1-1, when artificially screened. These genotypes may be evaluated in hot spot areas along with the resistant check to confirm their disease reaction. Hence these genotypes are considered as potential parents for Alternaria resistance breeding programme.Both of the two citrus diseases, Alternaria brown spot (ABS) and Anthracnose, caused by Alternaria and Colletotrichum spp., respectively, can produce leaf lesions which are hard to differentiate. These two diseases have been confused as causal agents of brown spot for over a decade in China. In this study, citrus leaves with or without brown spot were collected from Zhaoqing, Guangdong and Wanzhou, Chongqing, and were further used for the taxonomic and functional comparisons between the co-occurring Alternaria and Colletotrichum species. In the amplicon sequencing, the average relative abundance and the composition of Alternaria, but not Colletotrichum, increased (from 0.1 to 9.9, p = 0.059; and to 0.7, p < 0.05) and significantly altered (p < 0.01) with the brown spot in Zhaoqing and Wanzhou, respectively. Two representative isolates Alternaria sp. F12A and Colletotrichum sp. F12C, from the same brown spot, were proved with different virulence and host response activation to citrus leaves. F12A caused typical symptoms of brown spot with the average spot length expanded to 5 and 6.1 cm, and also altered the citrus global gene expression 48 and 72 h after inoculation. In addition, F12A enriched the expression of genes that were most frequently involved in plant defense. In comparison, F12C caused leaf spot limited to the wounded site, and its milder activation of host response recovered 72 h after inoculation. Our study indicates that the incidence of brown spot in China is caused by Alternaria species, and the ABS should be a fungal disease of major concern on citrus.
Colletotrichum
Colletotrichum capsici
Spots
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This study reported the test of toxicity of Trifloxystrobin and Tebuconazole with different ratios to the spore germination of Chinese cabbage Alternaria leaf spot [Alternaria brassicaal(Berk)Sacc.].The results indicated that,with the increase of the contentration,the 2 fungicides had stronger and stronger inhibition of the pathogen were mixed.The best effect of the concentration is 16.2 mg/L.While Trifloxystrobin and Tebuconazoa were mixed with a ratio of 0.5∶1,their cotoxicity coefficient(CTC)to Alternaria brassicae was 127.62,and the effect of improvement is remarkable.
Alternaria brassicae
Tebuconazole
Spore germination
Fungal pathogen
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Alternaria solani
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The sixteen varieties of cluster bean were screened against Alternaria blight of cluster bean caused by Alternaria cucumeriana var. cyamopsidis under field conditions at College Research Farm, College of Agriculture, Swami Keshwanand Rajasthan Agricultural University, Bikaner. Sixteen varieties screened against Alternaria blight under artificial inoculation conditions during Kharif 2016. Out of sixteen varieties of cluster bean, none was found highly resistant against Alternaria blight. Only one variety of RGC-986 was found resistant, whereas, five varieties viz., RGC-1003, HG-75, HGS-365, HGS-563, and GG-2 were found moderately resistant to Alternaria blight.
Kharif crop
Alternaria solani
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Alternaria leaf spot, caused by Alternaria spp., is a common foliar disease of sugar beet and other Beta vulgaris crop types. Known to be present in the United States since at least the 1950s, this disease has been found in all major sugar beet growing regions of the United States as well being reported as present everywhere beets are grown. Alternaria leaf spot symptoms are similar to several other common foliar diseases of beets including Cercospora leaf spot and the early stages of Phoma leaf spot. Symptoms and signs of this disease in the field do not provide enough information to help distinguish between diseases unless the viewer is readily familiar with the pathogen, especially when viewed with the unaided eye. Alternaria cultures can be identified to species using colony and conidial morphology on select culture media or using molecular markers. While not as common as Cercospora leaf spot, Alternaria leaf spot can result in significant reductions in yield and quality when not managed.
Cercospora
Phoma
Spots
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Alternaria brassicae
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Pseudomonas syringae
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Survey conducted in four districts of Northern Karnataka during kharif 2017-18, revealed that the disease severity of major foliar diseases viz., Alternaria leaf spot, Cercospora leaf spot and bacterial leaf blight ranged from 12 to 51, 8.50 to 30 and 3 to 13 per cent, respectively. The highest severity (51.00%) of Alternaria leaf spot was noticed at Chandrabanda village in Raichur district, maximum severity (30.00%) of Cercospora leaf spot was recorded at Indira Nagar in Raichur district. Whereas, highest severity (13.00%) of bacterial blight was noticed at Halagadda village of Kalaburgi district. The average highest Alternaria leaf spot and Cercospora leaf spot disease severity of 39.57 and 20.37 per cent, respectively was recorded in Raichur district. The average highest bacterial leaf blight severity of 9.28 per cent was recorded in Kalaburgi district.
Cercospora
Kharif crop
Curvularia
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Blight symptoms on pigeonpea were observed in alarming proportion since 2009 onwards in Andhra Pradesh state of India. Alternaria blight infected pigeonpea plants were collected from Andhra Pradesh state of India to isolate and characterize the pathogen. The isolate proved pathogenic on pigeonpea cultivar ICPL 87119. Genetic characteristics were analyzed based on the sequence of the rDNA-internal transcribed spacer (ITS) region. The phylogenetic tree based on rDNA-ITS analysis showed that the Alternaria alternata causing Alternaria blight in pigeonpea is very distinct from the other Alternaria isolate reported from different host. This is the first report of molecular identification of Alternaria alternata causing Alternaria blight in pigeonpea.
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Alternaria leaf spot and flower blight of marigold caused by Alternaria tagetica Shome and Mustafee is appearing in mild to severe form in Haryana. Field experiments were conducted to see the effect of weather parameters on development of Alternaria blight of marigold transplanted on different date. Alternaria leaf spot intensity decreased from 77.6 to 71.7 and 86.0 to78.1 during 2013 and 2014, respectively with delay in transplanting. Similarly, flower blight intensity also reduced from 85.4 to 80.4 and 88.7to 82.3% during both the years with delay in transplanting. Disease progression revealed that Alternaria leaf spot and flower blight intensity had significant negative correlation with weekly maximum and minimum temperatures and sunshine hrs whereas; morning and evening relative humidity had significant positive correlation.Maximum and minimum temperature 27.5±1.0°C and 7.5±1.0°C respectively, were found to be conducive for the development of Alternaria blight of marigold. Regression analysis indicated that the 83 per cent variation in Alternaria leaf spot and 87 per cent in flower blight intensity could be explained by weather parameter which was statistically highly significant.
Transplanting
Alternaria solani
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Experiments were conducted at Genetics and Plant Breeding Research Farm of N. D. University of Agriculture and Technology, Kumarganj, Faizabad (U.P.) to evaluate 15 promising genotypes of rapeseed-mustard against Alternaria blight caused by Alternaria brassicae (Berk) Sacc. and A. brassicicola (Schw) Wiltshire. It is the most destructive and major disease problem under eastern Uttar Pradesh in Indian condition causing both the quantitative and qualitative losses. The evaluation criteria for host resistance against the disease considered were the number and size of spot, number of conidia per spot on both the vegetative (leaf) and reproductive (pod) parts were regularly recorded at periodical intervals starting from the disease appearance till the physiological maturity of each genotypes. The indices which were considered for in built resistance were delayed appearance of visible symptoms, minimum number of spot and their size, number of conidia per spot as well as the minimum leaf defoliation. The disease appeared first in genotype T-9 (44 DAS) which was delayed in GSL-5 (53 DAS). The number of spot/10cm2, size, sporulation capacity in terms of conidia per spot varied invariably among the genotypes and significantly in some cases. The appearance of disease symptoms in the form of blighted spots varied invariably (44 to 53 DAS) in different genotypes. The delayed appearance of disease symptoms (53 and 52 DAS), lower number of spot / 10cm2 on leaf (3.07 and 3.65), pods (3.74 and 4.14), smallest spot size on leaf (3.54 and 3.05 cm), pods (1.22 and 1.27 cm2), number of conidia per spot on leaf (1230 and 1630), pods (130 and 150) were visualised in genotype GSL-5 and Pusa Aditya,respectively indicating a certain pattern and may be considered as attributes of disease resistance. Further, this fact was strengthened with minimum leaf defoliation (32.03 and 35.55%), PDI on leaf (12.35 and 14.16), pods (7.73 and 7.93) and ultimately the AUDPC calculated on leaf (486.70 and 551.90) and pods (282.85 and 291.05). Accordingly both the genotypes were grouped in moderately resistant (MR) category. The correlation coefficient (r) among parameters attributing to resistance behaviour worked out proved helpful in drawing the conclusion. Because very limited source of durable resistance are available, it may be suggested to exploit the two genotypes i.e.GSL-5 and Pusa Aditya for breeding programme against Alternaria blight.
Alternaria brassicae
Alternaria brassicicola
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