Wheat stripe rust (caused by Puccinia striiformis f. tritici Erikss.) causes severe yield losses worldwide. Due to the continuous appearance of new stripe rust races, resistance has been broken in most of the highly resistant genotypes in Egypt and worldwide. Therefore, looking for new ways to resist such a severe disease is urgently needed. Trichoderma asperellum strain T34 has been known as an effective bioagent against many crop diseases. It exists naturally in Egyptian fields. Therefore, in our study, the effectiveness of strain T34 was tested as a bioagent against wheat stripe rust. For this purpose, 198 spring wheat genotypes were tested for their resistance against two different P. striiformis f. tritici populations collected from the Egyptian fields. The most highly aggressive P. striiformis f. tritici population was used to test the effectiveness of strain T34. Highly significant differences were found between strain T34 and stripe rust, suggesting the effectiveness of strain T34 in stripe rust resistance. A genome-wide association study identified 48 gene models controlling resistance under normal conditions and 46 gene models controlling strain T34-induced resistance. Of these gene models, only one common gene model was found, suggesting the presence of two different genetic systems controlling resistance under each condition. The pathways of the biological processes were investigated under both conditions. This study provided in-depth understanding of genetic control and, hence, will accelerate the future of wheat breeding programs for stripe rust resistance.

Wheat stripe rust (Puccinia striiformis Westend f. sp. tritici; Pst) is a severe disease that affects wheat-growing areas worldwide. In the last few years, Pst head infection (PstHI) was recorded to cause severe yield damage in Egypt. Little information is known about PstHI. In the current study, a set of 34 Egyptian cultivars were evaluated for their Pst foliar infection (PstFI) and PstHI in two growing seasons (2021 and 2022) in Egypt. High genotypic variations in PstFI and PstHI were found. A very weak correlation was found between the resistance to PstFI and PstHI in both growing seasons. Therefore, the resistance to each symptom might be controlled by different genetic systems. The effect of PstFI and PstHI on kernel traits was investigated. PstHI was found to significantly reduce kernel width and weight in heavily diseased years. Therefore, a significant reduction in wheat yield and quality is expected in case of severe PstHI. Three Egyptian genotypes were resistant to PstFI and PstHI in both growing seasons. These genotypes could help in improving the resistance to both symptoms. However, due to the low genetic distance among them, looking for additional sources of resistance is recommended. In 2021, higher head infection was found compared with 2022. Highly significant differences in maximum temperature, minimum temperature, maximum dew point, and average dew point were found between the two growing seasons. Out of these four factors, dew point and ambient temperature were found to be possible reasons for increasing PstHI. Furthermore, 51 isolines carrying different resistance genes were included in the evaluation. At least ten stripe rust resistance genes were found to be effective against PstFI and PstHI. These ten genes should be included in future breeding programs to improve Pst resistance and understand the effect of climate change on Pst.