Morphological and SSR marker-based genetic diversity analysis of Indian mustard ( Brassica juncea L.) differing in Alternaria brassicicola tolerance

Alternaria black leaf spot disease of oilseed mustard is a primary cause of yield penalty not only in India but also throughout the world. To assess the degree of tolerance, 47 Indian mustard ( Brassica juncea ) genotypes were evaluated based on the performance against the causal pathogen Alternaria brassicicola . Genotypes were divided into six tolerance groups including resistant, highly tolerant, moderately tolerant, moderately susceptible, susceptible, and highly susceptible, keeping the nonhost resistant Sinapis alba as resistant control. Genotypes EC399312 and PAB-9511 were found to be the most tolerant. Fourteen morphological traits were evaluated which revealed considerable morphological variability among the genotypes. A number of seeds/siliqua and 1000 seed weight were positively correlated with yield per plant. Insignificant negative correlations had been found among plant height, days to maturity, and disease resistance with yield per plant. Correlation data indicate that seeds/siliqua and siliqua on the main shoot can be highly effective for higher grain yield. Genetic diversity of all genotypes was evaluated using simple sequence repeats (SSR) markers. The genotypes were evaluated for polymorphisms after amplification with 41 SSR primer pairs. Nineteen SSR markers in total were found to be highly informative with a polymorphic information content value > 0.50. The evaluation of genetic similarity and cluster analysis together with disease resistance provides some useful guides for assisting plant breeders in selecting suitable genetically diverse parents for the crossing program as well as for the development of mapping population.