126 Journal of Oilseed Brassica, 6 (1) Jan., 2015 Analysis of variability determinants in Alternaria-Brassica-interactions GS Saharan 1 , Naresh Mehta 1* , PR Verma 2 and PD Meena 3 1 CCS Haryana Agricultural University, Hisar-125 004, India; 2 Agriculture and Agri-Food, Canada, Saskatoon, S.K., Canada; 3 ICAR-Directorate of Rapeseed-Mustard Research, Bharatpur, 321 303, India *Corresponding author: nareshmehta282@gmail.com (Received: 10 December 2014; Revised: 15 December 2014; Accepted: 20 December 2014) Abstract The pathogenic variability in four species of Alternaria is reported to be governed by determinant attributes viz., pathological, symptomatological, morphological, cultural, nutritional, biochemical, genetical, molecular, proteome level, thermo, and fungicidal sensitivity. Initially, observations on variability in cultural characteristics and pathogenesis of different isolates of Alternaria were made in A. brassicicola- vegetables, A. brassicae–Brassica and A. raphani–radish host –pathosystem. A. alternata strains, from Crambe showed differences in their physiological and pathological characteristics; strain B was most virulent, strain A was moderately virulent, and strain C was least pathogenic on Crambe. Three races of A. brassicae viz., RM-1, RM-2 and V-3 virulent on rapeseed-mustard group of crops were identified. While race RM-1 was avirulent only on B. oleracea var. Capitata, race RM-2 was avirulent on both B. oleracea var. Capitata and B. oleracea var. Botrytis. Race V-3, from vegetable crops was most virulent on the all host differentials. Thirteen A. brassicae isolates evaluated on selected winter rape cultivars differed in their virulence. Three A. brassicicola pathotypes infecting siliquae of cauliflower were designated as aggressive, less aggressive, and non pathogenic. Alternaria raphani isolates were grouped as “wild Type” and “Variant Type”. Three A. brassicae isolates designated as A, C and D differed in their morphology, growth, sporulation, and cultural characteristics along with virulence on B. carinata. Four A. brassicae pathotypes from B. juncea were identified and designated as Bj-4, Bj-5, Bj-6 and Bj-7. Pathotypes DLK, RSR-I and GDP of A. brassicae were identified on the basis of their reaction on host differentials and symptomatological variations. Isolates of A. brassicae from crucifers were genetically similar in the highly conserved ITS region, but differed pathogenically. At molecular level, Alternaria isolates from crucifers showed polymorphism by RAPD analysis. Twelve polymorphic microsatellite loci (alleles ranged 2-10 with mean 3.5) were isolated from A. brassicicola isolates infecting crucifers. There were differences in the proteome level of virulent and avirulent A. brassicae from crucifers. In the absence of standard host differentials, some other parameters including symptomatology, morphology, cultural characteristics, nutritional requirement, biochemical changes, and thermo and fungicidal sensitivity were used to describe number of isolates in Alternaria –crucifers interactions without designating pathotypes. Key Words: Alternaria, crucifers, pathogenic variability, pathotypes, polymorphism, proteome level, RAPD analysis, Variability determinants Journal of Oilseed Brassica, 6 (1): 126-141, January 2015 Introduction The most dynamic and significant aspects in host-pathogen interactions is that characteristics of individuals within a species are not “fixed” in their morphology, physiology, biochemistry and pathogenicity. During reproduction, all individuals are expected to be different from each other, and from their parents in a number of characteristics, although they retain most similarities with them and belong to the same species (Agrios, 2005; Mehta et al., 2005a). When individuals are produced asexually, the frequency and degree of variability among the progeny are reduced greatly, but even then, certain individuals among the progeny will show different