No abstract

Anthracnose disease is one of the major economic constraints to chilli production in tropical and subtropical regions of the world and it is gaining much attention towards causes of damage in the field. Growing understanding has been based on conventional methods of characterisation of Colletotrichum species and its interaction with the host but it was not clear enough to recognise the differentiation among species, host-pathogen relationship and genetics of resistance in chilli. In this chapter, emphasis has been made on the evaluation of the isolates of Colletotrichum capsici causing chilli anthracnose for their morphological and cultural characteristics, pathogenic variability on chilli fruits and genetic diversity with the help of random amplified polymorphism (RAPD-PCR) analysis and designated into different major clusters. Simultaneously, screening of Capsicum genotypes against anthracnose for testing the resistance has been highlighted under in vitro condition. Further, on the basis of inheritance and the segregation ratio of resistance to susceptibility, gene controlling resistance at different fruit maturity stages has been discussed. More importantly, by QTL mapping, distribution of resistance gene/s located on chromosomes by using simple sequence repeats (SSR) primers, linkage groups are indicated. A number of complementary resistant component (host-parasitic interaction) controlled by one or multiple genes with small quantification effects have been emphasized. This information will be valuable to overcome the use of agrochemicals, impact of environmental factors and in the management of this serious threat to chilli through the development of resistant varieties as a donor candidate in commercial and resistance-breeding program.

The Alternaria blight or leaf blight (Alternaria brassicae) causes severe damage to cauliflower at curd formation and seed setting stage. Roving survey revealed that the disease incidence on cauliflower in different farmer's fields ranged from 10 to 40 % with an average incidence of 20 % in Uttar Pradesh. Twenty-three (23) isolates of A. brassicae were collected from different cultivars in Uttar Pradesh and characterized for cultural, morphological, pathogenic and molecular variations. Based on the pathogenicity, isolates of A. brassicae were rated as virulent or less virulent based on the percentage disease incidence on cv. Hajipur local. Most of the isolates showed smooth mycelial growth with circular, irregular margin and without concentric zonation. The colony colour is white, dark brown to light brown and pinkish in white. Significant morphological variations in conidial length, conidial width, and number of horizontal septa were observed in all the isolates. The maximum length of conidia ranged from 150 to 122 lm with 8 to 9 transverse and 2 vertical septation.Further the genetic diversity of isolates based on RAPD-PCR using sixteen random primers were produced on clarity, repeatability and the number of polymorphic bands in all the isolates. Cluster analysis of DNA fragments was performed using NTSYSpc V2.2 based on UPGMA method and Jacard coefficient. Based on the analysis the isolates represented four major groups with 75 % similarity.