MOLECULAR AND FIELD-BASED CHARACTERIZATION OF YELLOW RUST RESISTANCE IN EXOTIC WHEAT GERMPLASM

Field based assessment of wheat rust resistance was conducted for 29 advanced CIMMYT wheat lines and local checks across three locations of Pakistan vz. Peshawar, Mansehra and Bannu, complemented with molecular marker-based screening. A high disease pressure was prevalent across all locations associated with the favorable cold and wet climatic conditions prevalent during the year (2016). The maximum severity was recorded at Mansehra (up to 90%) followed by Peshawar (up to 50%) and Bannu (up to 45%). Significant variability existed amongst the tested wheat lines for yellow rust severity (ranging from 0% to 90%) and yield potential (ranging from 263 g to 757 g per 4.5 m(2) plot). Cluster analysis grouped 29 lines and three checks into four clusters. A better grain yield among the advanced lines was recorded for W-SA-104 (565 g per 4.5 m(2) plot), W-SA-115 (452 g) and W-SA-118 (447 g). None of the lines was resistance at every location and thus none had average coefficient of infection "ACI" = 0, though 26 lines were identified to possess partial resistance to yellow rust (with ACI < 20). Genotyping for the presence of resistance genes with molecular markers STS-7 (linked with Yr5), SC-Y15 (linked with Yr 17) and Xwmc-44 (linked with Yr29) revealed the highest frequency of Yr 17 (90.60%) detected in 29 wheat lines, followed by Yr29 (87.5%) detected in 28 wheat lines and then by Yr5 (50%) detected in 16 lines. Among 15 wheat lines (46.87%), three resistant genes were detected together. Variability detected in resistance response based on both field testing and molecular markers could potentially be exploited in wheat breeding to develop better resistance varieties for deployment at field level.