Pathogenic and molecular variability among Brassica isolates of Alternaria brassicae from India

Pathogenic variability was found among thirteen Alternaria brassicae isolates on twelve host genotypes in respect of five qualitative characters such as spot colour, periphery colour, central point colour, presence or absence of concentric rings, central point, yellow halo region and one quantitative character viz., % disease severity. Cluster analysis of pathogenic variability data revealed a close relationship between Nazirhat (SS-04), Jaipur (SS-07), Sachha Khera (SS-10) and Samalakha (SS-11) isolates. Use of 100 Random Amplified Polymorphic DNA decamer primers indicated genetic variability among the thirteen A. brassicae isolates. Almost all the isolates showed relationship according to their geographical origin except Sachha Khera (SS-10) and Hatikhuti (SS05) isolates. Pantnagar (SS-09) isolate was found closely related to Sachha Khera (SS-10) isolate. No variability could be located among the A. brassicae isolates by Internally Transcribed Spacer-Amplified Fragment Length Polymorphism molecular marker. Hence, pathogenic variability did exist among the isolates with variability also at genomic level but not in the highly conserved region of the genome of the pathogenic isolates of A. brassicae.