Genetic studies of stay green maize genotypes for Uganda.

Stay green is the ability of a plant to maintain photosynthetically functional green leaf area for longer periods even under water stress. The study was done to compare the physiological capacity of drought tolerant maize inbred lines to stay green under water stress conditions initiated at critical growth stages and to further understand the genes and gene action that controlled this performance with the general objective of contributing to breeding more drought tolerant maize varieties through generating knowledge on the stay green trait in maize genotypes targeting the drought prone ecologies of Uganda. The specific objectives of the study were (i) to determine the physiological capacity of the inbred lines to stay green, (ii) to determine the mode of inheritance for the stay green trait physiological determinants in the maize inbred lines, and (iii) to validate the quantitative trait loci (QTL) conferring the stay green trait in the maize inbred lines. Seventy-six maize inbred lines characterized for drought tolerance by CIMMYT and ten F1 hybrids from crosses between the best and worst performing of these inbred lines as regards stay green physiological determinants, were planted under a rain out shelter with a well-watered control (WW) and water-stress treatments applied at six (6WAP) and eight weeks (8WAP) after planting. In order to validate the genetic basis for the stay-green trait in the inbred lines, 28 simple sequence repeat (SSR) markers were used to analyze DNA extracted at the six-leaf stage from each of the inbred lines. With progress in days after flowering, data were collected on leaf pigmentation per unit leaf area (RC: LAUG), quantum yield of photosystem II activity (Phi2), non-photosynthetic quench (NPQt) and linear electron flow (LEF). RC: LAUG was maintained most under the 6WAP treatment by QTLs that were found in different genomic regions from those of other maize populations mainly by additive gene action. Non-photosynthetic quench was maintained most under the 6WAP treatment under the control of additive gene action. Phi2 and LEF were maintained most under the WW treatment with Phi2 controlled more by the environment than interallelic interactions while LEF was controlled mainly by interallelic interactions. It was therefore recommended that the significant physiological capacities of the inbred lines to stay green could be exploited for population improvement using methods that target both additive and non-additive gene action but with the effect of the environment taken into account.