Developing a differential system for designating the pathotypes of Puccinia hordei causing barley leaf rust in India

The virulence spectrum of leaf rust of barley (Puccinia hordei Otth.) has not been studied in India so far. This is a first study to design a system of pathotype nomenclature and know the virulence structure of pathotypes of P. hordei in India. All the available near-isogenic lines (NILs) of Rph genes, lines with known Rph genes, and other barley accessions including promising Indian barley cultivars were screened using 328 P. hordei isolates from different parts of India, Bhutan, and Nepal. Using a binomial system of nomenclature, 11 distinct pathotypes of P. hordei occurring in India were identified and named. A grouping of pathotypes in the 328 leaf rust samples analyzed since 1999, it was evident that pathotype H2 followed by H3, H7, H4 and H1 were the most predominant pathotypes. Based on the molecular studies, all the pathotypes were distinct and fell into three groups (A, B, and C). Group A further clustered into two subgroups A1 (4 pathotypes) and A2 (2 pathotypes). The virulence phenotype and molecular genotype based distinction of P. hordei pathotypes will help in the precise screening of barley germplasm and the identification of rust-resistant lines. The establishment of an Indian differential system for the designation of P. hordei isolates will also help in monitoring the shift in virulence patterns, predominance, and emerging of new pathotypes in the future and will help scientists of other countries to make comparisons with their virulences.