- Interaction for Spot Blotch Susceptibility in Indian Wheat: An Example of Inverse Gene-for-Gene Relationship.

The - system is an example of an inverse gene-for-gene relationship. The gene encodes a host-selective toxin (HST) which functions as a necrotrophic effector and is often responsible for the virulence of the pathogen. The genomes of several fungal pathogens (e.g., and ) have been shown to carry the gene. is a sensitivity gene in the host, whose presence generally helps a -positive pathogen to cause spot blotch in wheat. Cultivars lacking are generally resistant to spot blotch; this resistance is attributed to a number of other known genes which impart resistance in the absence of . In the present study, 110 isolates of strains, collected from the MEA and MEC megaenvironments of India, were screened for the presence of the gene; 77 (70%) were found to be positive. Similarly, 220 Indian wheat cultivars were screened for the presence of the gene; 81 (36.8%) were found to be positive. When 20 wheat cultivars (11 with and 9 with ) were inoculated with -positive isolates, seedlings of only those carrying the allele (not ) developed necrotic spots surrounded by a chlorotic halo. No such distinction between and carriers was observed when adult plants were inoculated. This study suggests that the absence of facilitated resistance against spot blotch of wheat. Therefore, the selection of wheat genotypes for the absence of the allele can improve resistance to spot blotch.