Journal of Crop Breeding

Bachground: Yellow rust caused by Puccinia striiformis is one of the most destructive diseases of wheat worldwide. In severe epidemics, disease damage can reach 100 %, and the yield can be completely destroyed. Finding sources of resistance and planting resistant cultivars is an effective method for alleviating rust damage. Race-specific genes can provide a higher level of resistance, but it can be broken by the emergence of new races of pathogens. Therefore, varieties with specific resistance genes often lose their resistance within a few years. To manage rust disease, the presence of several genes with varying degrees of resistance in cultivars is essential. In this research reaction of some cold climate wheat genotypes and cultivars to yellow rust at the seedling and mature plant stage were evaluated under field conditions.

Matherials and Methods: Yellow rust spores were collected from wheat fields in the Ardabil region (Northwest, Iran) and stored in a freezer at -80°C. Previously population of yellow rust in the Ardabil region was examined in the greenhouses of the Seed and Plant Improvement Institute (SPII, Karaj, Iran), and it was found to have virulence against Yr2, Yr6, Yr7, Yr9, Yr22, Yr23, Yr24, Yr25, Yr26, Yr27, YrA and YrSU resistance genes in wheat. Seeds of 29 genotypes including 22 promising cold climate genotypes related to yield comparison experiments and 7 irrigated and rainfed cultivars were provided from the cereals research department of the SPII. The Bolani cultivar was served as a sensitive control. Experiments were conducted in the field of Alarouq Agricultural Research Station, Ardabil. Inoculation was performed at the two-leaf stage of seedlings with a mixture of yellow rust spores and talcum powder (1:4). Note taking was done since symptoms had appeared on susceptible cultivars (at infection type 7 or higher). Genotypes and cultivars reactions were assessed using a 0-9 scale, with infection types of 7 or more considered as sensitive, infection types of 4-6 considered as moderate, and infection types of less than 4 considered as resistant. The genotypes tested at the seedling stage were also used to assess the response of the mature plant stage. The experiment was conducted in a randomized complete block design with 3 replications. In the seedling stage, infection type (IT) was evaluated, and in the mature plant stage, final rust severity (FRS), coefficient of infection (CI), and relative value of the area under disease progress curve (rAUDPC) were evaluated. Mean comparison and cluster analysis for the grouping of wheat genotypes/cultivars performed in SPSS 24 software. 

Results: Based on the results of analysis of variance, significant differences were observed between genotypes in resistance variables. Cluster analysis at the seedling stage placed the genotypes into three groups. The genotypes and cultivars including C-99-1, C-99-3, C-99-5, C-99-6, C-99-7, Heidari, Hoor, and Zarrineh were resistant. C-99-8, C-99-9, C-99-14, C-99-18, C-99-22, and, Jam showed moderate reaction. The others including C-99-4, C-9910, C-99-11, C-99-12, C-99-13, C-99-15, C-99-16, C-99-17, Heyran, Azar 2, Baran, and Bolani were placed in susceptible group. Cluster analysis at the mature plant stage classified the genotypes into three main groups. The first group included genotypes including C-99-1, C-99-2, C-99-3, C-99-4, C-99-5, C-99-6, C-99-7, C-99-8, C-99-9, C-99-10, C-99-11, C-99-13, C-99-14, C-99-15, C-99-16, C-99-17, C-99-18, C-99-19, C-99-20, C-99-21, C-99-22 and, cultivars including Heyran, Zarineh, Heidari, Hoor, and Jam showed resistance reaction. The cultivars Azar 2, Baran, and Bolani were placed in the susceptible group. In the third group, only the C-99-12 genotype was included, which showed a moderate level of partial resistance. Cluster analysis of the studied genotypes based on all traits examined at the seedling and mature plant stage placed them into three groups. The first group included genotypes C-99-1, C-99-2, C-99-3, C-99-4, C-99-5, C-99-6, C-99-7, C-99-8, C-99-9, C-99-10, C-99-11, C-99-13, C-99-14, C-99-16, C-99-17, C-99-18, C-99-19, C-99-20, C-99-21, C-99-15, C-99-22, and the cultivars Heidari, Zarrineh, Heyran, Hoor, and Jam, which were resistant both at the seedling and mature plant stages. The second group includes the genotype C-99-12, which was susceptible at the seedling stage but showed moderate partial resistance at the mature plant stage. The third group included the cultivars Azar 2, Baran, and Bolani which were susceptible at both seedling and mature plant stages. The genotype C-99-22 was semi-resistant at the seedling stage and semi-resistant to semi-susceptible at the mature plant stage.

Conclusion: Genotypes that showed resistance reaction at the seedling stage were also resistant at the mature plant stage therefore screening at the seedling stage is very cost-effective, result in reducing the workload for selection at the mature plant stage when a large number of genotypes are exixst. The cultivar Shiroodi is present in the pedigree of genotype C-99-8 and Heydari and Zarrineh cultivars therefore they contain genes for partial resistance. In the pedigree of Shiroodi, the cultivar Attila is present, which strengthens the possibility of the presence of resistance gene (s) in the C-99-8 genotype and Heydari and Zarrineh cultivars. The cultivar Kauz which contains the Yr9 resistance gene is present in the pedigree of C-99-16 genotype. The cultivar Pastor is observed in the pedigree of C-99-18 genotype. Genotypes/cultivars including C-99-2, C-99-5, C-99-11, C-99-13, C-99-15, C-99-16, C-99-17, C-99-19, C-99-20, and Heyran showed different levels of partial resistance (race non-specific or durable resistance) to yellow rust, which can be selected as a source of resistance, if they possess desirable agronomic traits.