Identification and transfer of ASI quantitative trait loci (QTL): A strategy to improve drought tolerance in maize lines and populations
1997
Ribaut, J.M. | Gonzalez de Leon, D. | Jiang, C. | Edmeades, G.O. | Hoisington, D.A.
When drought stress occurs just before or during flowering in maize, it delays silking and increases the anthesis-silking interval (ASI). Strong evidence associates an increased ASI with reduced grain yields in maize. In the present study, molecular markers were used to identify genomic segments responsible for the expression of ASI in maize, with the aim of using this information in marker-assisted selection (MAS)for reduced ASI. An F2 population of 260 individuals was genotyped at 150 loci. In 1992 and 1994, F3 families were evaluated under several water regimes in the field for ASI, several morphological traits, yield components and physiological drought variables. For ASI, six QTL (LOD scores greater than 2.5) were identified on chromosomes 1, 2, 5, 6, 8 and 10. These QTL account together for approximately 50 Per cent of the phenotypic variability which represented a change of 10.5 d for ASI. Transgressive segregation was observed for this trait. The four QTL segments contributed by the short- ASI line were responsible for a 6.8 d reduction in ASI, represented around 7 Per cent of the linkage map, and were stable over years and stress levels. Based mainly 071 these results and on the identification of QTL involved in the expression of grain yield, three different MAS projects are now being conducted at CIMMYT. These schemes, one based on backcrossing, another on line development from F3 families, and a third on changes in allelic frequencies in open-pollinated populations are discussed. Preliminary results suggest that MAS based 071 a strategy combining QTL identified under drought for ASI and grain weight should be a powerful tool to improve drought tolerance of tropical maize inbred lines, and perhaps also of open-pollinated populations.
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