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

Introduction
Stripe rust (Puccinia striiformis f. sp. tritici) and leaf rust (Puccinia triticina Eriks) are among the prevalent and devastating fungal diseases of wheat worldwide. Under favorable conditions, leaf rust can reduce the yield of wheat by 50%. The major damages of wheat rust diseases are the shriveling of grains and the damage of wheat tillerings. Depending on the severity of the epidemic condition, stripe rust can reduce the yield of wheat by 10-70%. The annual damage caused by rusts to wheat crops is estimated to be up to 50 million tons (about 5 billion dollars). Genetic resistance remains the most effective, sustainable, and economical strategy for controlling wheat rusts. Other methods such as agricultural and chemical methods alone are not effective enough to manage rusts. The objective of this study was to evaluate the response of promising wheat lines to stripe and leaf rust races to identify sources of resistance.

Materials and methods
To determine the virulence factors of rust pathogens to resistance genes in international standard and differential cultivars and lines associated with each rust, 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. The experiment at seedling stage employed a randomized complete block design with three replications. Each race was used separately to evaluate the differential cultivars. To identify sources of resistance to the studied stripe rust and leaf rust races, the reaction of 23 promising wheat lines (ERWYT-N99) was evaluated at the 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).

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

Discussion
Developing durable and effective resistance is a crucial strategy for mitigating the detrimental effects of wheat diseases and curtailing the excessive reliance on chemical pesticides.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 rust and leaf rust diseases.