Characterization of Dry-Land Wheat Germplasm for Stripe Rust (Puccinia striiformis f. sp. tritici) Resistance in Ardabil

Yellow (stripe) rust, caused by P. striformis f. sp. tritici, is one of the most important foliar diseases of wheat. The disease has been reported in temperate, cool, and higher altitudes regions, where wheat is grown. The widespread of the disease has always threatened wheat production and resulted in 30 to 100% losses in yield. Although chemical method is common throughout the world, it is not practical by farmers in developing countries. The most alternative practical way is to use genetic resistance which is economical and safely to environment. Two types of genetic resistance, including race-specific and non-race-specific resistance, are well known. Race-specific resistance operates based on the gene for gene hypothesis. Following the evolving of new races of pathogens, race-specific resistance becomes almost ineffective within 3–5 years. Non-race-specific resistance is controlled by small-effect (additive) genes and is long lasting. The wisely use of genetic resistance through the combination of race-specific and non-race-specific genes is suggested for the effective management of rusts. In view of the above, it is important to determine the properties of wheat germplasm for the detection of such diverse resistance. Therefore, the present study was performed to identify genetic sources with different resistance types to enhance the improvement of breeding operations for the release of cultivar in Iran.

In order to study of seedling reactions, a total of 191 dry land wheat lines were used. Seeds of each genotype (5-7 seeds) were planted in 7× 7 cm pots under controlled conditions in the greenhouses of Karaj. Seedlings were inoculated with two pathotypes of pathogen (6E158A+ and 6E150A+, Yr27). The inoculated Plants were transferred to a growth chamber at 10 ° C with 16 h of light and 8 h of darkness for 24 h. Plants were then transferred to greenhouses at 6–10 ° C temperature. 14-17 days later, seedling infection types were recorded based on a 0-4 scale (Stakman et al., 1962). The same number of studied lines at the seedling stage, were also used to evaluate the adult plant responses. The germplasm was cultivated at Ardebil Agricultural Research Station during the 2015-2016 cropping year. About eight grams seeds of each entry were planted in two-row plots of 1 m length with 30 cm distance. Plots were spaced at 65 cm. Infection types were recorded in the adult plant stage according to the method of Rolfs et al. Disease severity data were used to calculate the area under the disease progress curve (AUDPC). The relative area under the disease progress curve was also compared by comparing each line with the susceptible cultivar (assuming 100% susceptible cultivar value). In order to determine different resistance groups according to the method of Bux et al. (2012), lines with rAUDPC between 0-10 was considered as resistant group, rAUDPC = 11-30 as intermediate and lines with rAUDPC values above 30 were classified as susceptible.

Seedling evaluation using pathotype 6E158A+ showed that of 63 resistant genotypes, 31 genotypes were from winter wheat, 4 from durum wheat and 28 genotypes of spring bread wheat. The seedling reactions using pathotype 6E150A+, Yr27 indicated that of 64 resistant genotypes, 26 genotypes were of winter bread wheat, 8 genotypes of durum wheat and 30 genotypes of spring bread wheat. The results at seedling stage also revealed that 51 genotypes were resistant to both pathotypes, of which 24 were genotypes of winter bread, 4 genotypes of durum wheat and 23 genotypes of spring bread wheat. Of the 191 genotypes studied, 24 (12.5%) genotypes also showed resistance at both seedling (against to two pathotypes) and adult plant stages. In field conditions, 81 genotypes were susceptible and 110 (57.6%) were resistant. Among the resistant genotypes, the differences were observed based on the values of the relative area under the disease progress curve (rAUDPC). The response of winter wheat, spring wheat and durum wheat varied. Among the winter bread wheat, spring and durum wheat genotypes, 9 (12.5%), 38 (44.2%) and 4 (12.1%) genotypes had low levels of the area under the disease progress curve (rAUDPC = 0-10), respectively, and were classified as resistant group. A group of genotypes also had moderate values of the area under the disease progress curve (rAUDPC = 3-11), of which 16 (22.2%), 37 (43%) and 11 (33.3%) genotypes were of winter, spring, and durum wheat genotypes, respectively.

A number of genotypes having seedling resistance were identified with probability of resistance gene/genes; Yr3v, Yr3a, Yr4a, Yr4, Yr5, Yr10, Yr15, Yr16, YrCV, YrSD, or unknown genes. Most winter wheat genotypes lacked seedling resistance. Some of the genotypes had adult plant and slow rusting resistance (Non-race- specific or durable resistance) and this percentage was higher among spring bread wheat than winter wheat and durum wheat genotypes. This germplasm with various sources of resistance will be useful in integrating both types of resistance through the pyramiding of genes for durable resistance and eventually high-yielding resistant varieties will be introduced to farmers.