Genetic analysis and diversity of tropical quality protein maize (Zea mays L.) germplasm

Authors: NJERI, SUSAN - International Maize & Wheat Improvement Center (CIMMYT); MAKUMBI, DAN - International Maize & Wheat Improvement Center (CIMMYT); Warburton, Marilyn; DIALLO, ALPHA - International Maize & Wheat Improvement Center (CIMMYT); SEMAGN, KASSA - International Maize & Wheat Improvement Center (CIMMYT); JUMBO, MACDONALD - International Maize & Wheat Improvement Center (CIMMYT); CHEMINING, GEORGE - University Of Nairobi

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2017
Publication Date: 11/3/2017
Citation: Njeri, S., Makumbi, D., Warburton, M.L., Diallo, A., Semagn, K., Jumbo, M.B., Chemining, G. 2017. Genetic analysis and diversity of tropical quality protein maize (Zea mays L.) germplasm. Euphytica. 213(261):1-19. https://doi.org/10.1007/s10681-017-2048-4.
DOI: https://doi.org/10.1007/s10681-017-2048-4

Interpretive Summary: Maize (Zea mays L.) is an important source of carbohydrates and protein in the diet in sub-Saharan Africa, accounting for 17-60% of people’s total daily protein supply. Such dependence on maize as the primary or only protein source can lead to protein-energy malnutrition because of its inherent deficiency in two essential amino acids, lysine and tryptophan. Efforts to improve protein quality in maize led to the release of quality protein maize (QPM), which has double the amount of lysine and tryptophan compared to normal endosperm. Many African maize farms are found in the mid-altitude tropical agro-ecologies where a number of environmental or insect and disease constraints contribute to low yields. Breeding programs in eastern and southern Africa are incorporating QPM from unadapted maize into maize that is adapted to the mid-altitude growing conditions. Genetic diversity is the driver of plant breeding, and an increase would be a favorable outcome. Molecular markers can be used to ascertain if an increase in diversity levels in mid-altitude maize germplasm can be measured following introduction of the QPM lines from tropical breeding programs. This manuscript presents field data on 13 QPM inbred lines and hybrids created with them, and this data can be used to predict performance of these lines in hybrids in mid-altitude tropical growing conditions, thus guiding the creation of the best possible QPM hybrids. These 13 lines were also genotyped along with 114 other mid-altitude maize lines, but diversity levels original mid-altitude germplasm was already so high that inclusion of the QPM material did not increase it.

Technical Abstract: Maize (Zea mays L.) is an important source of carbohydrates and protein in the diet in sub-Saharan Africa. The objectives of this study were to (i) estimate general (GCA) and specific combining abilities (SCA) of 13 new quality protein maize (QPM) lines in a diallel under stress and non-stress conditions, (ii) compare observed and predicted performance of QPM hybrids, (iii) characterize genetic diversity among the 13 QPM lines using single nucleotide polymorphism (SNP) markers and assess the relationship between genetic distance and hybrid performance, and (iv) assess diversity and population structure in 116 new QPM inbred lines as compared to eight older tropical QPM lines and 15 non-QPM lines. The GCA and SCA effects were significant for most traits under optimal conditions, indicating that both additive and non-additive genetic effects were important for inheritance of the traits. Additive genetic effects appeared to govern inheritance of most traits under optimal and across environments. Non-additive genetic effects were more important for inheritance of grain yield but additive effects controlled most agronomic traits under drought stress conditions. Inbred lines CKL08056, CKL07292, and CKL07001 had desirable GCA effects for grain yield across drought stress and non-stress conditions. Prediction efficiency for grain yield was highest under optimal conditions. The classification of 139 inbred lines with 95 SNPs generated six clusters, four of which contained 10 or fewer lines, and 16 lines of mixed co-ancestry. There was good agreement between Neighbor Joining dendrogram and Structure classification. The QPM lines used in the diallel were nearly uniformly spread throughout the dendrogram. There was no relationship between genetic distance and grain yield in either the optimal or stressed environments in this study. The genetic diversity in mid-altitude maize germplasm is ample, and the addition of the QPM germplasm did not increase it measurably.