Changes in allelic frequencies in a tropical maize population under selection for drought tolerance
1997
Ribaut, J.M. | Hoisington, D.A. | Edmeades, G.O. | Huerta-Espino, J. | Gonzalez de Leon, D.
Selection for grain yield under severe water stress has often been considered inefficient because heritability generally declines as yield is reduced while environmental variance remains the same or increases. Under these conditions selection for secondary traits correlated with yield, Such as the anthesis- silking interval (ASI), may increase selection efficiency. Although ASI is a simple trait to measure in the field and has a relatively high heritability, it is not always possible to provide the stress levels required for efficient selection of this trait. CIMMYT physiologists conducted eight cycles of full-sib recurrent selection during the dry season for drought tolerance in the population 'Tuxpeno Sequia' based mainly on an index comprising increased grain yield and reduced ASI. In this study, we quantified changes in allelic frequencies over cycles of selection at loci of known map position. Through these changes identification of alleles involved in the expression of short or long ASI was possible, and may provide a rapid diagnostic tool in the future for screening lines or plants with potential drought tolerance in Tuxpeno germplasm. Changes in allele frequencies over cycles of selection (C0, C4 and C8; 116 plants randomly chosen from each cycle) were estimated using molecular markers. Loci distributed over the maize genome were assayed using RFLPs. Special attention was given to genomic regions responsible for expression of ASI, identified in a previous study using a cross between two inbreds derived mainly from Tuxpeno germplasm. There is strong evidence that the alleles of these two inbred lines are also present in this population. Allelic frequencies that either increased, decreased or remained stable were recorded for C8 relative to C0.
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