Screening of wheat genotypes against toxin and pathogen of Helminthosporium sativum
M. Patra and H. S. Chawla*
Genetics & Plant Breeding Department, G.B. Pant University of
Agriculture & Technology, Pantnagar, U.P., 263 145, India
Summary
Wheat cultivars were screened against pathogen of
Helminthosporium sativum and its crude toxin preparation. The
pathogen produced helminthosporal toxic metabolite substance(s) and
two pathostrains varied in their toxin producing ability. Bioassays
using intact and detached leaves of 21-day-old plants inoculated with
pathogen and crude toxin(s) revealed a similar reaction, thus
suggesting that wheat genotypes can be effectively screened against
culture filtrate/crude toxin(s) as pathogen inoculation.
Introduction
The fungus Helminthosporium sativum is the causal agent of seedling blight, root rot, head blight and leaf spot of cereals and grasses. This disease causes major losses in wheat production. Plant pathogens usually express several virulence mechanisms that increase their ability to colonize host plant tissues. Some of the general virulence mechanisms are the production of enzymes, plant growth regulators or toxins. These agents damage plant cells and cause the leakage of nutrients, providing an optimal environment for, the pathogen and reducing the capacity of plant .cells for defense (Keen 1992). Toxins have been implicated in virulence and are the products of pathogens and cause damage to plant tissues (Scheffer 1983). Tinline et al. (1960) reported that leaf spot lesions caused by H. sativum are highly variable. H. sativum grown in liquid synthetic medium produces a helminthosporal toxin (De Mayo et al. 1961). The production of toxic materials must be related to disease susceptibility of the host and virulence of the pathogen producing them. Hanneke et al. (1988) emphasized that prerequisites for the use of toxins as selective agents in in vitro selection are that they play an important role in pathogenesis and they act on the level where selection will be carried out. The work reported here relates to the extraction of toxic substances containing helminthosporal from two different pathostrains of H. sativum and screening of wheat cultivars against pathogen and a crude toxin preparation using intact and detached leaves.