Comparative Histology of Partial Resistance and the Nonhost Reaction to Leaf Rust Pathogens in Barley and Wheat Seedlings

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Abstract
The histological responses involved in partial resistance (PR) and nonhost reaction were compared in 3 barley and 3 wheat genotypes inoculated with Puccinia hordei and P. recondita tritici, the leaf rust pathogens of barley and wheat. Nonhost and PR reactions to the leaf rust pathogens were characterized by a high proportion of colonies that were arrested early (immediately after the formation of the 1st haustorial mother cells) and were associated with little or no plant cell necrosis. Eight barley genotypes, 4 with a low level and 4 with a high level of PR to P. hordei, were inoculated with the leaf rust pathogens P. hordei, P. recondita secalis and P. recondita tritici. The latter pathogen produced reproductive structures on all 4 barley genotypes with a low level of PR to P. hordei, suggesting that alleles for low PR to P. hordei also reduced the effectiveness of the reaction to P. recondita tritici.