Genetic analysis of drought tolerance in maize by molecular markers. II. Plant height and flowering

Drought is a serious agronomic problem, and one of the most important facto rs contributing to crop yield loss. In maize grown in temperate areas, drou ght stress occurs just before and during the flowering period: consequently , tolerance to water stress in this species is largely determined by events that occur at or shortly after flowering. The purposes of our investigatio n were: (1)to identify the chromosomal regions where factors conferring dro ught tolerance for traits related to plant development and flowering are lo cated and (2) to compare these regions with those carrying QTLs controlling these traits, in order to get indirect information on the genetic and phys iological basis of maize response to water stress. To this aim, we performe d a linkage analysis between the expression of male and female flowering ti me, anthesis-silking interval (ASI), plant height and molecular markers. Th e experiment was carried out under two environmental conditions, well-water ed and water-stressed, on a maize population of 142 recombinant inbred line s obtained by selfing the F-1 between lines B73 and H99 and genotyped by RF LP, microsatellites (SSR) and AFLP markers, for a total of 153 loci. Linkag e analysis revealed that, for male flowering time and plant height, most of the QTLs detected were the same under control and stress conditions. In co ntrast, with respect to female flowering time and ASI diverse QTLs appeared to be expressed either under control conditions or under stress. All of th e QTLs conferring tolerance to drought were located in a different chromoso me position as compared to the map position of the factors controlling the trait per se. This suggests that plant tolerance, in its different componen ts, is not attributable to the presence of favourable allelic combinations controlling the trait but is based on physiological characteristics not dir ectly associated with the control of the character.