Evaluation of wheat genotypes for resistance to bacterial leaf streak caused by Xanthomonas translucens pv. undulosa in field and greenhouse trials

Abstract

Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa, is a devastating cereal disease that is becoming more common in Iran. A cost-effective and realistic strategy to cope with BLS is planting of BLS-resistant cultivars. To discover BLS-resistant genotypes, 360 hexaploid wheat genotypes were selected and inoculated with a local strain of Xanthomonas translucens pv. undulosa in the field and greenhouse in two years (2019 & 2020). In the field experiments, disease reaction of wheat plants was assessed based on both percentage of disease incidence (PDI) and the percentage of disease severity (PDS). In the greenhouse experiment, disease reaction was evaluated as the disease severity (DS). The genotypes with PDS, PDI, and DS values ≤ 20% were considered BLS-resistant or semi-resistant. Genotypes with zero or very low PDS, PDI and DS during the first and second years were considered highly resistant to the disease. Despite resistant genotypes being more prevalent than susceptible genotypes in each year, genotype responses to BLS varied over the two years, but in both years, most genotypes showed a resistance response. Forty-six genotypes (12.8%) were consistently BLS-resistant across years in the field and greenhouse trials. In 2020, field BLS intensity ratings (PDI and PDS) were positively correlated with flag leaf width and days to maturity. In contrast, PDI and PDS were negatively correlated with plant height, peduncle length, and spike length. In 2019, no significant correlations were found between PDI, PDS, and phenotypic traits. Cluster heatmaps and principal component analysis (PCA) separated resistant and susceptible genotypes. In BLS-resistant genotypes, plant height, peduncle length, and spike length were significantly longer, but flag leaf width and days to maturity were shorter. This study identified new and diverse sources of resistance to BLS that could be used in wheat breeding efforts.