Immunization of Rice Plants against Helminthosporium Infection

Abstract

IMMUNIZATION has only recently attracted serious attention for controlling plant diseases. Following their classical studies on infection of potato tubers by Phytophthora infestans, Müller and Börger¹ postulated that “phyto-alexins”, produced by plants in response to infection, were responsible for resistance of plants to avirulent races of pathogens or to non-pathogens. On this basis, attempts have been made to induce resistance in plants to pathogens by pre-inoculation either with avirulent races or with non-pathogens, and success has been reported in a number of cases^2–7. Brown spot disease of rice caused by Helminthosporium oryzae is often severe in eastern India. Different rice cultivars are known to produce phytoalexin-like substances in response to infection by three important pathogens, Cochliobolus miyabeanus (perfect form of H. oryzae), Piricularia oryzae and Xanthomonas oryzae^8,9. Thus immunization of susceptible cultivars against H. oryzae by pre-inoculation with avirulent races seemed possible. Results of attempts to do this are summarized here.