Yield linkage drag in quality protein maize inbred lines and hybrids
Amegbor, Isaac Kodzo
MetadataShow full item record
The development of high yielding and stable quality protein maize (QPM) hybrids is important for increasing grain yield output per unit area, to support the fight against hunger and malnutrition in sub-Saharan Africa (SSA), as well as for feed supplement formulation for the animal and poultry industries. Despite the development of QPM genotypes with increased lysine and tryptophan content, important information is lacking on the yield potential of QPM genotypes compared to non-QPM (normal) genotypes. The main objective of this study was to quantify grain yield reduction (if any) due to the QPM trait. The specific objectives were to: (i) compare QPM and non-QPM inbred lines for yield and yield related traits, as well as quality traits, and determine stability for grain yield, (ii) compare QPM and non-QPM hybrids for yield and yield stability, (iii) estimate the combining ability for grain yield and quality traits of QPM and non-QPM inbred lines (iv) estimate the heritability, variance components, principal components, correlation coefficients, and do path analysis of grain yield, and agronomic and quality traits. In this study, 130 single cross hybrids were developed from 33 QPM and non-QPM inbred lines and four testers (two QPM and two non-QPM). Five hybrid checks (two QPM and three non-QPM, all single cross hybrids) were included, obtained from the International Maize and Wheat Improvement Center, Zimbabwe. The 135 hybrids together with the 40 inbred lines were evaluated in South Africa and Zimbabwe during the 2017/2018 and 2018/2019 cropping seasons. The inbred lines were evaluated at seven locations using a 5 x 16 alpha lattice design, while the hybrids were evaluated at 13 locations using a 5 x 27 alpha lattice design with two replications. In the field experiments, two plants per plot were selfpollinated for the determination of zein, tryptophan, amylose and starch, protein, oil, moisture and fibre contents. In the inbred line trials, the top six performing lines outyielded the best yielding check by 15%. Although the top two inbred lines were non-QPM, three of the six top yielding inbred lines were QPM. The QPM inbred line average yield was 0.29 ton ha-1 higher than for non-QPM inbreds. Inbred lines 39, 27 and 10 had protein content above 9%, while lines 2, 5 and 16 had tryptophan concentrations above 0.09%. The best performing hybrids were a QPM cross of line 11 x CZL15049 (entry 41) followed by a non-QPM hybrid involving line 28 x CZL15049 (entry 108). The best QPM hybrid outperformed the best non-QPM hybrid by 8.81%. In addition, the best QPM hybrid, genotype 41, outperformed the best non-QPM check (Pioneer) and best QPM check (CBI) by 50.45 and 52.24%, respectively. Despite this, QPM hybrids yielded 13.90% lower than non-QPM genotypes on average. The additive main effects and multiplicative interaction (AMMI) and genotype main effect plus genotype by environment interaction (GGE) biplots identified genotypes 108 and 12 as the most stable and high yielding hybrids. QPM hybrid 41 and non-QPM hybrids 108 and 12 were the highest yielding genotypes. Both additive and non-additive genetic effects were important in the expression of measured traits, with non-additive gene action controlling the inheritance of grain yield. Inbred lines 11, 14 and 28 and non-QPM tester CML444 showed desirable general combining ability effects for grain yield. Based on the specific combining ability values, crosses 41, 85, 99, 105, 105 and 121 were identified as the best hybrids across the 13 locations for grain yield. Hybrids 45, 69 and 6 had a high quality index, while hybrids 45 and 57 had high tryptophan content. Hybrids 51 and 37 had high values for starch and oil contents, respectively. Additive genetic effects were predominant in the control of the quality traits. Broad sense heritability estimates were higher than 80% for the traits measured. Most of the hybrids displayed heterosis for grain yield, with some having very high values. In conclusion, QPM inbred lines yielded higher than non-QPM lines, but QPM hybrids yielded 13.9% less than non-QPM hybrids. So it would seem that there is yield drag associated with increased protein quality in hybrids in this specific set of material. There were, however, specific QPM hybrids that had excellent and stable yield, which can be considered for commercial release.