Inheritance of yellow rust resistance and glutenin content in wheat.

Abstract

Knowledge of traits inheritance is a prerequisite for any plant breeding program. Wheat cultivars ‘Pirsabak-85’, ‘Khyber-87’, ‘Saleem-2000’, ‘Pirsabak-04’, ‘Pirsabak-05’ and ‘Shahkar-13’ were crossed in 6 × 6 diallel fashion during 2010-11 at the Cereal Crops Research Institute (CCRI), Nowshera - Pakistan to explore genetic basis of early maturity, some production traits, resistance to yellow rust (Puccinia striiformis West.f.sp. tritici) and glutenin contents in wheat grains. Six wheat cultivars along with respective F1 and F2 populations were evaluated during 2011-12 and 2012-13 at the CCRI, Nowshera. Significant differences were observed among F1 and F2 populations and their parental cultivars for all traits across both years. In F1 generation, cross combinations Shahkar-13/Khyber-87 while in F2 populations Pirsabak-04/Khyber-87 and Pirsabak-05/Shahkar-13 showed earliness and had lesser days to heading and maturity. Cross combination, Pirsabak-85/Pirsabak-04 exhibited maximum spike length, grains per spike, grain yield, biological yield and yellow rust resistance in F1 generation. In F2 generation, Pirsabak-05/Shakar-13 had lesser days to maturity with higher flag leaf area, 1000-grain weight, grain yield and yellow rust resistance. Based on scaling tests, additive dominance model was found partially adequate for all the traits in F1 and F2 generations. According to Hayman's genetic analysis, major components of genetic variance i.e. additive (D) and dominance components (H1, H2) were important in the inheritance of the studied traits. In F1 generation, additive (D) component was greater than dominance (H1, H2) for earliness, morphological and yellow rust resistance traits which indicated predominant role of additive gene action in the inheritance of these traits. Dominance components were larger than additive for yield and yield related traits, suggesting the involvement of non-additive gene actions in the expression of these traits in F1 generation. In F2 generation, additive component was greater than dominance for tillers per plant, 1000-graint weight, grain yield per plant, harvest index, and yellow rust resistance while for other traits the component D was smaller than H1 and H2, demonstrating the primary role of non-additive gene actions. In both generations, the additive and non-additive gene actions for various traits were validated by the ratios of average degree of dominance and Vr-Wr graphs. In F1 generation, high estimates of broad-sense (0.80 to 0.99) and narrow-sense (0.70 to 0.91) heritability values were recorded for days to heading, plant height, peduncle length, flag leaf area and 1000-grain weight. However, estimates of broad-sense (0.56 to 0.99) and narrow-sense (0.13 to 0.49) heritability were low to high for days to maturity, tillers per plant, spike length, spikelets per spike, grains per spike, grain yield per plant, biological yield, harvest index and yellow rust resistance in F1 generation. In F2 generation, broad-sense heritability ranged from 0.78 to 0.97 and narrow-sense heritability ranged between 0.59 and 0.65 for tillers per plant, 1000-grain iii weight, harvest index and resistance to yellow rust. However, in F2 generation, the estimates of broad-sense heritability ranged between 0.75 and 0.95 and narrow-sense heritability ranged from 0.33 to 0.53 for days to heading, days to maturity, peduncle length, flag leaf area, spike length, spikelets per spike, grains per spike, grain yield per plant and biological yield. In both generations, mean squares due to GCA were significant for days to heading and maturity, plant height, peduncle length, flag leaf area, tillers per plant, spike length, spikelets per spike, grain per spike, 1000-grain weight, grain yield, biological yield, harvest index and yellow rust resistance. The SCA mean squares were significant for most of traits in both generations. Based on GCA effects, Pirsabak-05 was considered to be the best general combiner for yield traits and rust resistance in F1 generation. However, in F2 generation, cultivar Shahkar-13 appeared as best general combiner for earliness and yield traits, and rust resistance. The F1 hybrid Pirsabak-85/Pirsabak-04 and F2 population Pirsabak-05/Shahkar-13 were the promising cross combinations and had favorable effects for majority of the traits. Greater variances due to σ2SCA than σ2GCA for most of the traits in F1 and F2 generations, suggested the predominant role of non-additive gene actions in the expression of these traits. Parental cultivars, F2 and F3 populations along with check genotypes (Chinese Spring and Pavon-76) were analyzed for glutenin subunits through SDS-PAGE. Eight alleles were identified at different loci in both sets of wheat genotypes. Three alleles (Null, 1 and 2*) were identified at Glu-A1 locus, three allelic pairs (7 + 8, 7 + 9 and 17 + 18) were observed at Glu-B1 and two allelic pairs (5 + 10 and 2 + 12) were located at Glu-D1 locus. Pavon-76 had allele '2*' at Glu-A1 locus, '17 + 18' at Glu-B1 and '5 + 10' at Glu-D1. Similarly, Chinese Spring as a marker was with 'Null' allele at Glu-A1 locus, '7 + 8' at Glu-B1and '2 + 12' at Glu-D1. The allelic combinations i.e., 2*, 17+18, and 5+10, showing that high quality scores were observed among parental genotypes, F2 and F3 populations indicating their effectiveness in future breeding programs. Knowledge of gene actions involved in the expression of various traits might be useful in deciding the breeding procedure to be used for improvement of these traits. Promising parental cultivars (Pirsabak-05 and Shakar-13), F1 hybrid (Pirsabak-85/Pirsabak-04) and F2 population (Pirsabak-05/Shakar-13) revealed best performances in form of earliness, resistance to yellow rust and increased grain yield. These genotypes could be be used in future for developing early maturing, rust resistant and high yielding wheat cultivars.