Evaluation of Macroscopic and Microscopic Components of Partial Resistance to Leaf Rust in Durum Wheat

Leaf rust, caused by the fungus Puccinia triticina, is considered one of the most important foliar diseases in durum wheat. Hypersensitive resistance (HR) may be rapidly overcome by the pathogen when resistant cultivars are grown on a large acreage or following changes in virulence in the pathogen population. Prolonging the durability of the resistance requires uses of other types of resistance such as partial resistance (PR). In this study, six durum wheat lines provided by the International Center for Corn and Wheat Improvement (CIMMYT) with a high level of PR to leaf rust were studied in monocyclic tests in a growth chamber. Inoculations were performed on both primary and fifth leaves using the Spanish race DGB/BN. UV fluorescence microscopy was employed to determine microscopic components of the resistance, such as the number of early aborted infection units not associated with plant cell necrosis (EA−) and relative colony size (RCS) of the established infection units. Macroscopic components of PR such as latency period, infection frequency and uredinium size were measured as well. All six resistant lines were characterized by a higher EA− and smaller RCS respect to the susceptible control ‘Don Rafael’. Line 3 showed the highest level of PR. It had 22% of EA− compared with 4% in the susceptible control, and the smallest RCS (17% respect to RCS of ‘Don Rafael’) at adult plant stage. Both EA− and RCS had a high heritability (more than 97%) and the correlation with macroscopic parameters (latency period and uredinium size) was also high (significant at 0.001 level). Hence, PR to leaf rust in these durum wheat genotypes has been revealed at microscopic level (higher EA− and smaller RCS).