Inter and intra-specific diversity in Alternaria species infecting oilseed Brassicas in India

Abstract

The work was initiated to determine diversity in pathogen population of Alternaria blight which results in up to
60% yield losses in the world. It is a most prevalent fungal disease of oilseed Brassica in North and North-
West regions of India where approximately 80% of Brassicas are grown. Fifty five single spore isolates of
Alternaria species (32 of A. brassicae, 20 of A. brassicicola and 3 of A. alternata) were isolated from
infected leaf samples collected from 8 states of India. The purified isolates were evaluated for their
morphological, cultural, biochemical and molecular characteristics, and also preserved in DMSO and
glycerol. Significant variations (P< 0.05) were observed in sporulation intensity, spore morphology, radial
growth and carbohydrate concentration among isolates of each species. Analysis of RAPD banding profiles
also showed a high level of genetic diversity varying between 57-78%, 78-92% and 89-100%, among the A.
brassicae, A. brassicicola and A. alternata isolates, respectively. Extensive variations were observed in
isolates for all the parameters studied, but no correlation could be established. This study, thus indicates that
a significant non-specific variation exist between isolates infecting different species and varieties of
Brassica in India. This is the first report of comparative evaluation of the three Alternaria species from
different locations, on three different media and cryopreservation.