Molecular and field based characterization of yellow rust resistance in wheat germplasm across locations in Pakistan
Rust disease response is used to assess the resistance status of breeding lines, which is required to be tested across location and complemented with molecular markers. The current study was designed to characterize yellow rust resistance in 29 introduced advanced CIMMYT wheat lines along with three check varieties across three contrasting wheat growing regions (Peshawar, Mansehra and Lakki-Marwat) during wheat season 2015-16. A high disease pressure was observed across all three locations as favorable cold and wet climatic conditions prevailed during 2015-16. The maximum disease was recorded at Mansehra (up to 90%) followed by Peshawar (up to 50%) and Lakki-Marwat (up to 45%). There was a significant variability amongst the tested wheat lines for yellow rust severity and in yield potential. Among the advanced lines, W-SA-104, W-SA-115 and W-SA-118 had better grain and biological yield. Based on disease and yield parameters, cluster analysis of 29 wheat lines along with three checks grouped wheat lines into four clusters. None of these wheat lines showed resistance at every location (Average coefficient of infection "ACI" = 0). The maximum co-efficient of infection (55) was recorded at Mansehra whereas the minimum (0) was recorded at Peshawar and Lakki-Marwat. Twenty-six of these wheat lines were identified to possess partial resistance to yellow rust (with ACI < 20). Genotyping for the presence of resistance gene markers STS-7 (linked with Yr5), SC-Y15 (linked with Yr17) and Xwmc-44 (linked with Yr29) revealed the highest frequency of Yr17 (90.60%), followed by Yr29 (87.5%) and Yr5 (50%). The three resistant genes together were present only in 15 wheat lines (46.87%). Our results thus revealed the presence of variation in resistance response based on both field testing and molecular markers which could be utilized in wheat breeding to develop better resistance varieties to be exploited at field level.