Rathi, A.S.Pawan Kumar2017-06-032017-06-032013http://krishikosh.egranth.ac.in/handle/1/5810014853The stem rot disease caused by Sclerotinia sclerotiorum (Lib.) de Bary is the most serious fungal disease and causes maximum damage in Indian mustard (Brassica juncea). The present investigation on cultural, morphological, pathogenic and genetic variability was carried out with fourteen isolates of S. sclerotiorum collected from mustard growing areas of the country. All the isolates exhibited variations in their colony colour, type of growth and mycelial growth. HSR, FTH, SRS and DBW isolates showed dirty white colony colour, while rest of the isolates showed whitish colony colour. The variation in type of growth was also observed as BWL, MHR and BHR isolates showed fluffy and regular type of growth; ALW and JLN isolates showed fluffy but irregular growth, while rest of the isolates showed sparse and regular type of mycelial growth. All isolates showed significant differences in mycelial growth up to 72 hours of incubation, while non- gnificant differences were observed after 96 hours of incubation among the isolates. Significant variations were observed in number of sclerotia formation, size and pattern of sclerotia formation among the isolates after 10 days of incubation. Sufficient variability was also observed for number of apothecia per sclerotium. Isolates were also found to vary in their per cent disease intensity and significant host × pathogen interaction on different rapeseed-mustard genotypes under screen house and field conditions. HSR isolate was the most pathogenic with mean disease intensity of 53.1 and 60.8% under field and screen house conditions, respectively, while ALW was the least pathogenic isolate with disease intensity of less than 30% under both the conditions. Some isolates showed moderately resistant reaction on one genotype while, susceptible to highly susceptible reaction on rest of the genotypes. Some of the isolates could not be clearly differentiated pathogenically; however, they showed variable reactions on these genotypes. The variation was observed for stem breaking of different genotypes and formation of varying numbers of sclerotia after inoculation of S. sclerotiorum isolates under field conditions. The ITS (Internal transcribed spacer) analysis differentiated the fourteen isolates into two major clusters at similarity coefficient of 0.38. Cluster A was constituted by only one isolate ALW and Cluster B was a large group containing 13 isolates. Cluster B was further divided into two groups C and D which occupied nine and four isolates, respectively.enDiseases, Genotypes, Fungi, Pathogens, Biological phenomena, Planting, Genetics, Mustard, Sclerotinia sclerotiorum, Biological developmentThesis