Genetics of production traits and stripe rust resistance in bread wheat under rainfed and irrigated conditions

Abstract

Understanding inheritance and biotic stress resistance is of crucial importance for the genetic improvement of any field crop. Wheat (Triticum aestivum L.) is one of the most important cereal crop. In the present studies, 8 × 8 diallel crosses were conducted in wheat during 2014-15. All the 56 F1 hybrids along with parental genotypes were evaluated during 2015-16 under irrigated and rainfed conditions to determine the genetic control of various traits and to find out resistance to stripe rust by using molecular markers. The experiment was conducted in completely randomized block design with 3 replications at the Department of Plant Breeding and Genetics, The University of Agriculture Peshawar-Pakistan. Molecular study was carried out in the Institute of Biotechnology and Genetic Engineering, The University of Agriculture Peshawar and at Plant Breeding Institute, The University of Sydney, Australia. Pooled analysis showed highly significant genotypes × environment interaction for all the studied characters except days to maturity, final rust severity (FRS) and relative area under disease progress curve (rAUDPC). Under both conditions among the genotypes significant differences were observed for the studied parameters. Among the parents, PS-13, JB and PS-05 performed well under both conditions. Under irrigated condition, cross combinations, Lal-13 × JB, KW ×PS-05 and JB × AH while under rainfed condition, cross combinations, PS-05 × PJ-11, Tat-96 × AH and JB × AH, showed best performance for yield and yield related characters. Under irrigated conditions maximum best parent heterosis was observed for cross combinations, KW × Lal-13, Lal-13 × PS-05, Tat-96 × PJ-11 and Lal-13 × JB, whereas, under rainfed conditions, JB × AH, PJ-11× Tat-96 and PS-13 × AH were best heterotic combinations for yield and yield contributing traits. Natural disease infestation was scored for disease infection under both conditions. Under irrigated condition cross combinations, Lal-13 × JB, KW × PS-05, JB × AH, KW × PS-13, Tat-96 × KW and PS-05 × AH and under rainfed condition cross combinations, PS-05 × PJ-11, Tat-96 × AH, JB × AH, Lal-13 × AH and Tat-96 × PS-05 showed best performance for most of the traits. Under both ii environments the genotypes were classified into different groups of high, moderate and low level of partial resistance on the basis of FRS, rAUDPC and average coefficient of infection (ACI) values. Through molecular study, using simple sequence repeats (SSRs) markers, the presence of yellow rust resistance genes, Yr5, Yr17 and Yr18, were confirmed in 76.5%, 78.1% and 37.5%, respectively, of the material studied. Under rainfed condition genotypes PS-05 × AH, PS-05 and PS-13 × PS-05 and under irrigated condition, Lal-13 × JB, PS-05 × Lal-13, PS-05 × Tat-96 and JB × PS-05 showed partial resistance in field. The rust resistant genes conferring partial resistance were present either individually or in combinations of two or three in the genotypes. In diallel analysis, under both irrigated and rainfed conditions highly significant dominant ‘b’ and additive ‘a’ genetic effects were observed for the studied characters except spikelets spike-1 having non-significant gene effects under both conditions and grains spike-1 having non-significant dominant gene effect under rainfed condition. Additive-dominance model was from complete to partially adequate for various characters under both environments. Similarly, for the studied characters both dominant (H) and additive (D) genetic components were significant under both environments. High broad and narrow sense heritability was estimated for all of the studied parameters except days to maturity, days to heading, 1000-grain weight and biological yield plant-1 which possessed low narrow sense heritability. Mean squares of SCA and GCA analysis were highly significant for the studied parameters except spikelets spike-1 and spike length which remained non-significant under both conditions, whereas, fertile tillers plant-1 remained non-significant under irrigated conditions only. SCA mean squares were smaller than GCA mean squares for yield and yield contributing traits indicating preponderance of additive genetic effects. Under irrigated condition cross combinations, PS-05 × JB, Tat-96 × PJ-11 and AH × PS-05 were best specific combiners while under rainfed condition AH × JB, AH × Tat-96 and PJ-11 × PS-05 were the best specific combiners for yield and yield associated traits. Based on overall results, crosses combinations, Lal-13 × JB, PS-13 × AH and PS-05 × AH were better yielders and had lower yellow rust severity and are recommended to be exploited in future breeding programs. These results suggested the significance of additive and dominant genetic variability and through integrated use of diallel crossing technique or pedigree method with recurrent selection, efficient improvement is possible.