Vegetative compatibility grouping of Alternaria brassicicola causing black leaf spot in cauliflower

Abstract

A study was conducted to understand the relationship between pathogenicity and vegetative compatibility groups (VCG) of thirty-two A. brassicicola isolates causing black leaf spot in cauliflower. Nine isolates were highly pathogenic as the spot size produced by them are > 1 cm in diameter where as eight isolates were moderately pathogenic as they produced spot size of 0.6–1 cm and fifteen isolates were least pathogenic as the spot size were 0.2–0.5 cm in diameter. One hundred forty-four chlorate-resistant mutants were isolated from A. brassicicola isolates on water agar and PDA both contains 3% potassium chlorate whose number varied from 1 to 7. These mutants were further classified into three different phenotypes: nit M, nit 1, and nit 3. The largest group of mutants proved to nit 1 (36.8%), followed by nit 3 (32.6%), nit M (15.3%), wild type (9.3%) and unknown (6.0%). The anastomosis between nit mutants were also observed under microscope. Based on complementary reactions these thirty-two isolates were grouped into five arbitrary designated VCG which can be further used for the diversity analysis of A. brassicicola isolates.