Phenotypic evaluation of all-stage (ASR) and adult-plant resistance (APR) to leaf rust (Puccinia triticina Eriks) in an Iranian bread wheat germplasm.

Genetic resistance is the most effective and environmentally friendly strategy for controlling leaf rust (Puccinia triticina Eriks), the most common and devastating foliar diseases that affect wheat production worldwide. In order to identify the source of resistance to leaf rust, an Iranian bread wheat germplasm composing 217 landraces and 103 commercial varieties was evaluated at both seedling and adult plant stages. The seedling experiment was conducted in the form of randomized complete block design (RCBD) using twelve Puccinia triticina isolates under greenhouse conditions, and adult plant stage assessment was performed in two field environments (Ahwaz and Karaj) during the 2020-2021 growing season. The results showed that there was a high level of genetic variation among the genotypes at seedling stage (p < 0.01), however susceptibility was predominant in all twelve isolates, with only 4% of genotypes showing resistance reaction to all isolates. The genotypes showed wide-spectrum differences based on FDS, CI and AUDPC indeces at adult plant stage in field conditions. The genotypes were classified to four classes based on cluster analysis, constructed from integrated seedling and adult plant stage data as follows; resistant (66%), moderately resistant (13%), moderately susceptible (18%), and susceptible (3%). Notably, 17 genotypes were resistant at the adult plant stage but susceptible at the seedling stage, suggesting the existence of APR genes; like Lr34, Lr46, Lr67, and Lr68, providing slow-rusting resistance. In general, the results of the study suggest that Iranian wheat germplasm may hold as a genetic resource to breeding programms with durable resistance, leading to sustainable wheat production and food security.