Investigating the reaction of resistance to stripe rust disease (Puccinia striiformis f. sp. tritici) in commercial cultivars and promising wheat lines (candidate to be introduced as a commercial cultivar)

Yellow or stripe rust caused by the fungal pathogen Puccinia striiformis f. sp. tritici is one of wheat's most prevalent diseases. It poses a significant threat to wheat production worldwide, including in Iran. Diseases are considered one of the most significant biological challenges that can reduce wheat performance by up to 20% globally. Given the total wheat production, this incurs an economic impact of several hundred million dollars. Annual losses caused by rust diseases in wheat are estimated to reach up to 50 million tons worldwide. Integrated management using agronomic and chemical control methods and genetic resistance (developing resistant cultivars) is considered the most effective strategy for controlling this disease. Identifying sources of resistance at various genetic levels within wheat germplasm is crucial in national wheat breeding programs for establishing effective and heritable genetic resistance against this disease.

Two distinct races with high and low virulence were obtained from the yellow rust pathogen collection of the Pathology Unit at the Seed and Plant Improvement Institute for phenotypic screening of resistance in wheat cultivars and promising lines at the seedling stage (under greenhouse conditions). The elimination of urediniospores from other rust species was achieved through several rounds of purification on the susceptible Bolani cultivar using the rub-in method. To identify effective and stable resistance sources against yellow rust pathogen races, the resistance reaction of 41 commercial cultivars and 45 promising wheat lines (from four climatic regions of the country), along with the sensitive cultivar Bolani (as a control), was evaluated at the seedling stage against two yellow rust races from the pathogen collection of the Pathology Unit at the Seed and Plant Improvement Institute in Karaj, with high and low aggressiveness (174E191A+, Yr27 and 6E134A+, Yr27), and at the adult plant stage in the research station of the Ardabil (Moghan) Agricultural and Natural Resources Research and Education Center.

In the 2023 and 2024 growing seasons, the climatic conditions in the Moghan Plain were highly conducive to the emergence and spread of yellow rust disease. The weather was characterized by cool temperatures ranging from 8 to 17 degrees Celsius and high relative humidity from late March to mid-May. During the 2024 growing season, the prevalence of yellow rust disease was notably more severe in various regions of the country, particularly in the northern areas. The resistance genes Yr1, Yr5, Yr10, Yr15, Yr24, YrSU, and YrSP were identified as effective resistance genes against the yellow rust races. The results indicated that approximately 56% of the commercial wheat cultivars exhibited acceptable resistance reactions, while about 44% lacked effective resistance (showing intermediate to susceptible reactions). Furthermore, around 87% of the promising wheat lines displayed acceptable resistance reactions, whereas about 13% lacked effective resistance. The yearly variation in results could be attributed to differences in the abundance and virulence of dominant pathogen populations in the region, and environmental conditions affecting the two years.

The findings of this study indicate that heritable genetic resistances are present in most of the commercial cultivars currently cultivated extensively and in the lines nominated for introduction as new commercial wheat cultivars. In the present study, the number of wheat cultivars and promising lines exhibiting resistance to yellow rust races was greater than those showing susceptibility and intermediate susceptibility. This indicates that effective resistance genes have been incorporated into the new wheat lines within breeding programs. New wheat lines must possess high yield potential and desirable agronomic traits and demonstrate acceptable levels of resistance to the most significant wheat diseases, particularly rusts, to be introduced as commercial cultivars. If they do not possess such resistance, they should be discarded, as environmental conditions during the growing season can favor rust pathogen activity, especially yellow rust, leading to significant yield losses. The identified resistant cultivars and lines from this research can be utilized in breeding programs to develop wheat cultivars resistant to yellow rust.