Sources of FHB Resistance, Genetics and Mapping of Stem Rust Resistance in Kenyan and Ethiopian Spring Wheat Germplasm

Abstract

Fusarium head blight (FHB or scab) and stem rust are important diseases of wheat. Fusarium graminearum is considered the primary causal agent of FHB. This study evaluated 215 wheat genotypes from Kenya and Ethiopia for their response to F. graminearum in inoculated and mist-irrigated nurseries established in St. Paul, MN in 2016, St. Paul, MN in 2017 and Crookston, MN in 2017. Six genotypes with stable resistance across the three test locations were identified. Positive associations were identified between FHB index, VSK, and DON and negative associations were identified between FHB index, plant height, and heading dates. The response of select genotypes was confirmed under greenhouse conditions. These studies identified resistance sources that can be used to improve the resistance levels in Kenyan and Ethiopian wheat germplasm. Stem rust caused by Puccinia graminis f. sp. tritici remains a threat to wheat production in East African wheat growing regions. In this study, we characterized the genetics of stem rust resistance, identified QTLs and markers associated with the resistance in spring wheat line CI 14275. The RILs together with their parents were evaluated at the seedling stage in a biosafety level 3 greenhouse against Pgt races TTKSK and TRTTF and in the USDA-ARS Cereal Disease Lab greenhouse against Pgt races TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the US in 2016, 2017, and 2018. One and three complementary genes conferred resistance to races TTTTF and RTQQC, respectively. The QTL QSr.cdl-2BS.2, that conferred resistance in Kenya and Ethiopia was validated and the marker Excalibur_c7963_1722 was shown to have potential in marker assisted selection. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The QSr.cdl-3B.1 is likely Sr12, QSr.cdl-4AL.1 is postulated as Sr7a, QSr.cdl-6BL.1 is likely Sr11, and QSr.cdl-6AS.1 appears to be a new QTL. Combination of QSr.cdl-2BS.2, QSr.cdl-3B.1, and QSr.cdl-6AS.1 has the potential to reduce stem rust severity in Africa. The work presented on FHB and stem rust provides resources for wheat improvement in East Africa.