Quantitative genetic analysis of agronomic and kernel endosperm traits in quality protein maize (QPM) and investigations of the putative nutritional value of contaminated QPM crops.
Year: 2008
Type: dissertation
Abstract: The importance of maize in sub-Saharan Africa and the potential of quality protein \nmaize (QPM) to alleviate the nutritional gap caused by lack of access to adequate \nprotein rich foods were highlighted. Frustrations from complex inheritance systems of \nthe QPM trait leading to calls for more information on the inheritance and stability of \nthe QPM trait, fear of total loss of the QPM trait due to the recessive nature of the \nopaque-2 gene to the wild type gene in normal endosperm maize when QPM and \nnormal endosperm maize coexist, lack of information on the nutritional value of \ncontaminated QPM grain, and poor linkages with the smallholder farmers were all \ncited as drawbacks in the promotion and adoption of QPM. Therefore the objectives \nof the study were: \n1) To solicit the participation of smallholder farmers in the development and \nsetting up of QPM breeding goals, objectives and dissemination strategies; \n2) To estimate general combining ability (GCA), specific combining ability (SCA) \nand reciprocal cross effects on anthesis days, quality traits and grain yield \namong the publicly available elite QPM inbred lines; \n3) To compare experimental QPM hybrids with selected check cultivars, and \nnormal endosperm maize hybrids for grain yield performance and kernel \nendosperm modification scores; \n4) To evaluate QPM hybrids for grain yield and kernel endosperm modification \nscores in selected sub-Saharan Africa target environments. \n5) To determine the level of normal endosperm maize pollen contamination that \ncan occur in quality protein maize without loss of nutritional superiority; \n6) To estimate the average levels and the patterns of foreign maize pollen \ncontamination in QPM crops coexisting with normal endosperm maize \nvarieties. \nThe contribution of smallholder farmers in setting breeding goals and dissemination \nstrategies for QPM was solicited. One major finding was that the kernel endosperm \nqualities of landrace “Hickory King” need to be incorporated into new QPM varieties \nso as to encourage adoption. Farmers preferred getting information on QPM varieties \nthrough their local Agricultural Research and Extension (AREX) officers. \n \nA diallel study of 36 F1 QPM hybrids and their reciprocals was conducted across \nseven environments for agronomic traits and three environments for nutritional value \ntraits. There were significant differences for all traits analysed using Griffing Method 3 \nmodel 1. General combing ability effects were significant and important in the control \nof anthesis days, kernel endosperm modification, protein content, tryptophan content, \nand Quality Index (QI). Specific combining ability effects were highly significant and \nimportant in the control of grain yield. There were significant SCA effects for anthesis \ndays and QI but the proportions were lesser than the corresponding GCA effects in \nboth traits. Kernel endosperm modification had significant GCA effects and \nnonsignificant SCA effects. \nReciprocal-cross differences were significant for anthesis days, tryptophan content \nand QI. Nonmaternal effects were significant for tryptophan content whilst both \nmaternal and nonmaternal effects were significant for QI and anthesis days. \nNonmaternal effects were relatively more important than maternal effects in all the \ncases where there were significant reciprocal-cross differences. The cross with the \nhighest SCA effects for grain yield was CZL03016/CML144. The most desirable \ncross with the lowest anthesis days was CZL03016/CML144 whilst the most \ndesirable inbred line with the lowest anthesis GCA effects was CZL03016. The \ninbred line with the most desirable GCA effects for protein content, tryptophan \ncontent and QI was CML264Q. Inbred line CML264Q crossed to CZL03016 had \nsignificant SCA effects for QI. The most desirable GCA effects for kernel endosperm \nmodification were associated with inbred line CZL03016 followed by CZL01006. \nMaternal effects for both tryptophan content and QI were associated with inbred line \nCML264Q. \nGenotype by environment interaction effects across all the seven environments were \nsignificant for grain yield and kernel endosperm modification. Check hybrids \nperformed better than experimental hybrids for grain yield but were not different for \nkernel endosperm modification. The normal endosperm maize hybrids were \nsignificantly better for both grain yield and kernel endosperm modification. However, \nin all the comparisons the best check or normal endosperm maize hybrid was not \nsignificantly better than the best experimental or QPM hybrid, respectively. The most \ndesirable score for kernel endosperm modification was from the cross of CZL01006 \nto CZL03016 though not significantly different from the check hybrid with the best \nscore. AMMI1 was the best model for kernel endosperm modification scores and \nAMMI2 was suitable for grain yield. Both environments and hybrids were diverse. \n \nGrain yield of most hybrids was not stable with specific adaptation to environments. \nThe most stable hybrid with no specific adaptation was CML176/CML181f with a \nmean yield of 6.51t ha-1. \nThe putative nutritional superiority of normal endosperm maize pollen contaminated \nQPM as measured by the QI depended on the environmental conditions. The \nmoisture stressed environment (CIMMYT Harare) had a lower QI value (0.858) and a \nlower tolerance to pollen contamination of 15.3% whereas the grain produced under \nnear to optimum growing conditions (ART farm) had a higher QI value (0.915) and a \nhigher tolerance to pollen contamination of 31.9% before total loss of nutritional \nsuperiority. Thus contaminated QPM grain had nutritional superiority up to a certain \npoint before total loss of nutritional superiority. \nGeostatistical analysis was used to determine the levels and patterns of pollen \ncontamination that occur when QPM and normal endosperm maize crops coexist \nunder conditions minimising both temporal and geographical isolation to the lowest \npossible levels for the two independent crops. Higher pollen contamination levels \nwere restricted mostly to the sections of the QPM crop proximal to the rows of normal \nendosperm maize crop, with the central parts of the QPM crops experiencing \nrelatively low levels of contamination. For the four experiments (QCS200711, \nQCS200712, QCS200721 and QCS200722) in which the thresholds to nutritional \nsuperiority were determined, 87.9%, 94.8%, 62.2% and 65.6% of the crop areas \npassed for superior QPM grain, respectively. Estimates for average contamination \nlevels of homogenous mixtures of grain from each of the nine experiments were \nbelow 20% contamination. The contamination levels were far less than previously \nthought. \n“Hickory King” kernel quality attributes were important in breeding QPM varieties for \nthe smallholder farmers. Parents of the 72 hybrids were diverse for the agronomic \ncharacters studied and three of the experimental hybrids were found to be adapted \nand comparable to the check varieties. Quality protein maize tolerance to foreign \npollen contamination without loss in nutritional superiority depended on growing \nconditions. The coexistence of QPM and normal endosperm maize without total loss \nof QPM nutritional superiority was feasible.
Author: Lewis Machida
Language: English
Topic: Genetics and Plant Breeding
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2255903158