Two improved tropical maize composites, TZL COMP3 and TZL COMP4; representing complementary heterotic pools have been subjected to four cycles of reciprocal recurrent selection (RRS) for two decades to enhance varietal cross performance. The objectives of this study were to evaluate the effect of selection on genetic gain in heterosis for grain yield and other agronomic traits of these composites. Ten parental populations representing the C0 to C4 of each composite and their crosses plus a varietal check were evaluated in a trial at eight environments in Nigeria. Grain yield of the varietal crosses increased with selection by 3.1% cycle–1. Mean grain yields of the C4 × C4 varietal cross exceeded that of a popular improved reference variety by 23%. Selection also reduced anthesis-silking interval, improved ear characteristics, phenotypic appeal and resistance to foliar diseases. Mid-parent heterosis (MPH) increased from 4% at C0 × C0 to 24% at C4 × C4. The average rate of genetic gain in heterosis for grain yield in population crosses was 3.1% possibly because of presence of non-additive gene effects. The results of our study present the potential usefulness of the advanced selection cycle as sources of diverse inbred lines with improved combining ability as well as improved varietal crosses that can be multiplied and deployed in areas with limited market access.
Afiah, S.A.N., Darwish, I.H.I. 2002. Combining ability analysis and heterosis in relation to salinity and drought stress for yield and its attributes of bread wheat. J. Agric. Sci. Mansoura Univ. 27 :8033
A study was conducted during 2008–2010, to estimate heterosis for yield component traits and protein content in bread wheat under normal and heat-stress environment by utilizing a set of 45 half diallel cross combinations, involving 10 diverse parents. Analysis of variance revealed significant differences for the two environements, whereas differences over the years were non-significant for all the traits. The pooled data over the years, exhibited highly significant differences for all the traits under both normal and heat-stress environments. The number of tillers/plant exhibited maximum degree of standard heterosis under normal and heat-stress environment (with value of 12.62% and 53.75%), respectively. In general, spike length (16.02%) and number of grains/spike (52.10%), showed higher magnitude of standard heterosis under normal environment than heat-stress environment, whereas number of tillers/plant (53.75%) and gain filling duration (43.68%) showed higher standard heterosis in heat-stress environment than the normal one. For grain yield/plant, 1000-grain weight and protein content, the number of cross combination showing standard heterosis were almost same in both the environments. The ten crosses, out of forty-five crosses, namely HD 2733/WH 542; PBW 343/UP 2425; HD 2687/PBW 343; PBW 343/UP 2382; PBW 343/HD 2285; WH 542/UP 2425; PBW 343/PBW 226; UP 2382/HUW 468; PBW 343/WH 542 and PBW 226/HD 2285 can be used to select transgressive segregants for normal as well warmer wheat growing areas. These ten combinations can be used by involving, the trait grain filling duration, tillers per plant, spike length, grains per spike, 1000-grain weight to improve grain yield for warmer areas. In all 45 cross combinations, six cross combinations were identified for better per se performance for grain yield as well as protein content under heat-stress environment. These combinations may thus be used for developing superior genotypes through fixation of heterosis are also supported by high SCA. Besides, results of present study also revealed ample scope for developing transgressive segregants involving some of these parents to develop high yielding genotypes in wheat suitable for heat stress environments.
Five inbreds (UDL1, UDL4, UDL5, UDL6, 126) from our preliminary maize improvement program for increased starch content and some of their hybrids were grown in 2008 at the field of Horticultural Institute, Debrecen University. Three chemical parameters (starch-, protein-, oil content) and the weighing of one physical trait (thousand-kernel weight) were analyzed. The starch content varied from 64.29–70.80% in lines and from 70.84–72.29% in case of hybrids. Protein content in the dry material was between 9.04–12.62% in case of the parent lines and it was 7.61–9.56% in the single cross hybrids. Strong negative correlation (r = −0.834**) was found between starch and protein content of the examined hybrids. The oil content varied from 2.70–3.64% and 2.87–3.39% in lines and hybrids, respectively. The thousand-kernel weight (TKW) varied between 213.6–341.3 g in case of the lines and it was 314.3-426.3 g in hybrids. Significant differences were found among hybrids in TKW (SD5% = 34.66%). Heterosis was experienced in the starch content of UDH6 hybrid. Both the relative and absolute values of heterosis for starch content and kernel weight were positive for each single cross hybrid.
. 1999. Exploitation of heterosis: Uniformity and stability. In: Coors, J.G., Pandey, S. (eds), The Genetics and Exploitation of Heterosis in Crops. ASA-CSSA-SSSA, Madison, WI, USA, pp. 319–333.