Evolution of host selectivity, host resistance factors and genes responsible for disease development by Streptomyces scabies

Abstract

Common scab of potato is a severe disease affecting tubers. This disease caused by soil-borne filamentous bacteria related to the genus Streptomyces. Generally streptomycetes were saprophytic in nature but a few species were modulated themselves to cause disease in underground parts of several plants. The causal agent of the potato common scab is the bacteria Streptomyces scabies which has worldwide occurrence. The pathogen produces certain phytotoxins like thaxtomin, which is one of the major virulence (vir) factors responsible for the common scab disease. A number of genes are responsible for production of this toxin and are clustered in a particular region with certain other vir factors in the genome of S. scabies commonly referred to pathogenicity associated island (PAI). The mobilizing and transferring abilities of the PAI are considered responsible for emergence of new pathogenic strains of Streptomyces. Synthesis of certain aromatic amino acids and phytohormones shows inhibitory effects on production of the toxin thaxtomin. This chapter deals with factors responsible for pathogenesis, host selectivity, non-host resistance, and evolution of new pathogenic strains of S. scabies. © 2017 by Apple Academic Press, Inc.