Field evaluation of resistance to powdery mildew in bread wheat germplasms

Wheat powdery mildew caused by the biotrophic fungus Blumeria graminis f. sp. tritici, is a serious threat to wheat production in many regions of the world. This disease can reduce the yield up to 45% and reduce the quality of the grains by affecting the flour protein. Due to the adoption of high-yield crop systems that require high use of nitrogen fertilizers and high irrigation, as well as due to climate changes towards milder winters and increased rainfall in wheat production areas, the importance of powdery mildew disease is also increasing. One of the most useful strategies to control powdery mildew disease is to identify the sources of resistance among germplasm, which is also known as the most economical method among farmers. This research was conducted to identify resistant genetic samples to powdery mildew in the bread wheat collection of the National Plant Gene Bank of Iran.

The plant materials of this research were 173 accessions of bread wheat from the collection of the National Plant Gene Bank of Iran received from different countries, which were investigated to identify the sources of resistance to powdery mildew under natural incidence conditions at the research stations of Gorgan and Sari as the disease hotspots during three crop years (2018-2021). A two-digit scoring system was used to evaluate the response of the genotypes to the disease, in which the first digit is measured based on the infection development in plant height and the second is measured based on the disease severity in terms of the infection percentage on flag leaf surface. Then, by combining these two criteria, disease development and disease severity, the infection coefficient was calculated and used for the statistical analysis. K-means cluster analysis was used to group the germplasm and determination function analysis based on principal components was used to confirm the cluster analysis results. The relationship between the reaction of accessions in different years and locations was also investigated using multidimensional scaling analysis, and then the stability of the studied accessions over the experimental years and locations was investigated using the Wricke’s equivalence stability criterion based on the infection coefficient.

The results of this experiment showed that the average coefficient of infection during the studied three crop years varied from 0.05 to 0.29 percentage in Sari station and from 0.25 to 0.29 percentage in Gorgan station. The studied genetic materials were separated into five groups using K-means cluster analysis, and the fourth group consisting of 68 accessions was identified as the most resistant group. Based on the results of this experiment, the accessions KC 5292 (Turkey) and KC 5824 (Austria) were identified as the resistant genotype, and the accessions KC 5389, KC 5579 and KC 5476 (Iran), KC 5772, KC 5773 and KC 5384 (Afghanistan), KC 5133 and KC 5147 (Portugal), KC 5715 (Japan) and KC 5801 (unknown origin) as the resistant to semi-resistant genotype, and had the most stable response to the disease in various environments.

The results of the current research showed that there is a suitable genetic capacity to identify sources of powdery mildew resistance in wheat genetic stocks. The superior and resistant genetic materials identified in this research can be used to improve resistance to powdery mildew in wheat in the future breeding programs.