| Six advance wheat lines namely B4N11, B6N5, B6N12, BRF1, BRF3 and BRF17 and four wheat cultivars namely Zam-04 (ZM04), Kohat-10 (KT10), Pirsabak-08 (PS08) and Janbaz (JZ) were crossed in line × tester mating to develop 24 F1 hybrids. The resultant hybrids along with parents were evaluated during cropping season 2012-13 at Cereal Crops Research Institute (CCRI), Pirsabak, Nowshera, Pakistan under rainfed environment, using RCB design with 3 replications. General combining ability (GCA), specific combining ability (SCA) and narrow sense heritability for maturity and yield components traits were determined. The main objective of the research was identification and proper selection of best performing wheat parental genotypes and best F1 crosses, based on GCA and SCA estimates. Significant differences were observed among the wheat genotypes for all the studied traits. The estimates of σ 2gca and σ 2sca and its ratio (σ 2gca/σ 2sca) indicated that non-additive genetic expression were pre-dominant for most of traits studied. Line BRF3 and testers ZM04 were good general combiners for most of traits under consideration, while F1 hybrids B4N11 × PS08, B4N11 × JZ, BRF1 × ZM04, BRF1 × KT10 were best specific combiners observed for several important traits including grain yield plant-1 which can be subsequently utilized in future wheat breeding to develop high yielding new wheat cultivars from transgressive segregants recovered in latter generations.

Wheat yellow rust (YR) caused by Puccinia striiformis is lethal for the leaf photosynthetic process, which substantially affects yield components and ultimately causes drastic yield reduction. The current study aimed to identify all-stage YR resistance linked QTLs in the best cross-combination. Experimental materials were phenotyped for disease severity in YR-hot spot area at Cereal Crops Research Institute, Pirsabak Pakistan in Khyber Pakhtunkhwa province in 2019 and 2020 and 2020 and 2021 Rabi seasons. The AN179 × KS17 was found to be the best cross combination, which showed high resistance to YR, whereas crosses AN179 × PK15 and PR129 × PK15 demonstrated susceptibility to YR with high disease severity. The recombinant inbred lines (RIL) F₂ wheat population Annong-179/Khaista-17 demonstrated highly desirable YR resistance and yield component traits. Simple sequence repeat (SSR) markers were used to genotype the RIL population and their parents. Three novel QTLs linked to all-stage YR resistance were found on chromosomes 2BS, 3BS and 6BS, which explained 1.24, 0.54, and 0.75 phenotypic variance, respectively. Incorporation of the newly identified novel YR-resistance associated QTLs into hybridization wheat breeding program could be effective for marker-assisted selection of the improved and sustainable resistance.

Yellow rust (YR) globally affects wheat crops. It may turn into an epidemic, resulting in significant yield losses if the environment is suited to YR spread. The provision of resistant wheat cultivars is a sustainable protection strategy against YR. The current study aimed to use a combination of classical analytical tools to identify potential wheat lines through screening under YR stress for utilization in YR-resistance breeding. A total of 14 parents, which included 9 lines and 5 testers, were formed into 45 cross combinations via line × tester mating format. The tested germplasm was grown in a triplicate randomized full-block design, under optimal and yellow rust (YR)-stress conditions. Data were recorded on different morphological, physiochemical, yield and component traits at appropriate crop stages. A pre-combining ability analysis revealed significant inter-genotype variations. A combining ability study identified non-additive gene action in the inheritance of most of the investigated traits. Four potential parents (PR128, AN179, KS17 and WD17) and two crosses (PR128 × WD17 and AN179 × KS17) retained higher combining ability values for yield traits under YR-stress. A cluster analysis based on the overall performance found divergent classes among the screened genotypes. The clustering of different genotypes was shifted under YR-stress, which suggests variable genotypic response. Through factor analysis, we assessed and confirmed genotypes performing consistently under YR-stress. The identified genotypes may be used for disease-resistance breeding in wheat. Based on their positive correlation with grain yield, we suggest the use of peduncle length and tillers per plant as phenotypic markers for wheat selection and breeding. The knowledge base generated through the current study will add to the ongoing research on sustainable wheat breeding program.

Yellow rust (YR) epidemics have affected wheat productivity worldwide. YR resistance (Yr) is eminent in wheat; however, it is continuously invaded by evolving YR pathogen Puccinia striiformis (Pst.). Understanding the Yr genes’ diversity among the available germplasm is paramount to developing YR-resistant cultivars. In this study, 14 wheat genotypes were screened for their relative resistance index (RRI) and Yr genes/QTL via linked microsatellite markers. RRI screening categorized the studied genotypes into susceptible (7; 8.45 ± 0.25) bulks (p < 0.001). Genetic analysis using 19 polymorphic microsatellite markers revealed 256 alleles, which were divergent among the three resistance bulks. Markers Xbarc7 and Xgwm429 showed the highest allelic diversity in comparison to Xbarc181, Xwmc419, SCAR1400, and Xgwm130. Resistant bulk showed associated alleles at Yr18 gene-linked markers Xgwm295, cssfr6, and csLV34. Other RRI-associated alleles at markers Xbarc7 and Xbarc101 showed weak and moderate linkages, respectively, with the Yr5 gene; whereas, a moderate association was noted for the Yr15 gene-linked marker Xgwm11. Marker Xwe173 linked with the Yr26 gene showed associated alleles among the susceptible bulk. Cross combinations of the parental lines forming recombinant inbred lines (RILs) demonstrated net higher RRI implying favorable allelic recombination. These results support reports and field observations on novel Pst. races that triggered Yr26, Yr5, and Yr15 busts in recent past. This study further implies that pyramiding all stage resistance genes (Yr5, Yr10, Yr15, and Yr26) with adult plant resistance genes (Yr18 and Yr62) should provide sustained YR resistance. The associated alleles at Yr genes-linked markers provide a basis for marker-assisted YR resistance breeding in wheat.