Genetic investigation of the resistance of promising wheat lines to virulence factors of stripe rust and leaf rust races

Stripe rust (Puccinia striiformis f. sp. tritici) and leaf rust (Puccinia triticina Eriks) are among the prevalent and devastating fungal diseases of wheat worldwide. The use of genetic resistance is the most effective, sustainable, and economical strategy for controlling rusts. The first step in wheat breeding programs to create the effective genetic resistances (resistant varieties) to rust disease is to know the characteristics of rust isolates in different regions, and in the next step, is to identify resistance sources to produce resistant varieties. The objectives of this study were to determine the virulence factors of rust pathogens to resistance genes in international standard and differential cultivars and lines associated with each rust and to evaluate the response of promising wheat lines to stripe and leaf rust races to identify resistance sources.

Five stripe rust isolates collected from the regions of Karaj, Sari, Zarqan, Moghan, and Mashhad, and three leaf rust isolates collected from the regions of Gorgan, Moghan, and Ahvaz were identified. To identify the sources of resistance to the studied stripe and leaf rust races, the reaction of 23 promising wheat lines (ERWYT-N99) was evaluated at seedling stage (rusts greenhouses of Seed and Plant Improvement Institute, Karaj, Iran) and adult plant stage (research station of the Ardabil Agricultural and Natural Resources Research and Education Center, Moghan, Iran). The resistance reaction of wheat lines to five stripe rust isolates and three leaf rust isolates at the seedling stage was evaluated in separate experiments based on randomized complete block design with three replications. The resistance reaction of wheat lines at the adult plant stage was also investigated under field conditions and natural contamination of stripe and leaf rusts using disease progression parameters on the plant and disease severity percentage appeared on leaves.

The results of determining the race of the isolates showed that the stripe rust isolates collected from Karaj, Sari, Zarqan, Moghan, and Mashhad regions included the races of 14E158A+, Yr27; 142E158A+, Yr27; 6E134A+, Yr27;, 166E62A+, Yr27; and 6E142A+, Yr27; respectively, and the leaf rust isolates collected from Gorgan, Moghan, and Ahvaz included FDTTS,  FKTTS, and FJTTS, respectively. The resistance genes Yr1, Yr4, Yr5, Yr10, Yr15, Yr24, YrSU, YrSP, and YrCV were identified as the effective resistance genes against stripe rust races, and the resistance genes Lr1, Lr2a, Lr9, Lr19, and Lr28 were identified as the effective resistance genes against leaf rust races. The results showed that there was a significant genetic difference between the reaction of promising wheat lines to stripe and leaf rust races. Based on the results of the reaction of wheat lines to stripe rust races in both seedling and adult plant stages, wheat lines were divided into two main groups (resistant and semi-resistant to semi-susceptible), so that except for lines number 21 and 22 (with semi-resistant to semi-susceptible reaction), other wheat lines showed acceptable resistance to stripe rust races. Based on the reaction of promising wheat lines to leaf rust races in both seedling and adult plant stages, the lines were also classified into three main groups (resistant, semi-resistant to semi-susceptible, and susceptible), and lines number 1, 3, 11, 14, 21, and 22 showed acceptable resistance to leaf rust races.

Coclusion:

Developing durable and effective resistance is one of the crucial strategy for mitigating the detrimental effects of wheat diseases and reducing the excessive reliance of chemical fungicides. In addition to exhibiting high yield potential and desirable agronomic traits, newly developed wheat lines must harbor an acceptable level of resistance to the most prevalent wheat diseases, particularly rusts, to qualify for commercialization. The presence of rust pathogens poses a significant threat during the growing season. If environmental conditions favor their pathogenicity, the damage inflicted can be substantial, warranting the development of robust resistant varieties. The resistant lines identified in this study can be used as sources of resistance in breeding programs to develop wheat varieties resistant to stripe and leaf rust diseases.