Analysis of variability determinants in Alternaria-Brassica-interactions

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. brassicicolavegetables,
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.