LOCATING GENES ASSOCIATED WITH ROOT MORPHOLOGY AND DROUGHT AVOIDANCE IN RICE VIA LINKAGE TO MOLECULAR MARKERS

This research was undertaken to identify and map quantitative trait lo ci (QTLs) associated with five parameters of rice root morphology and to determine if these QTLs are located in the same chromosomal regions as QTLs associated with drought avoidance/tolerance. Root thickness, root:shoot ratio, root dry weight per tiller, deep root dry weight per tiller, and maximum root length were measured in three replicated exp eriments (runs) of 203 recombinant inbred lines grown in a greenhouse. The lines were from a cross between indica cultivar Co39 and japonica cultivar Moroberekan. The 203 RI lines were also grown in three repli cated field experiments where they were drought-stressed at the seedli ng, early vegetative, and late-vegetative growth stage and assigned a visual rating based on leaf rolling as to their degree of drought avoi dance/tolerance. The QTL analysis of greenhouse and field data was don e using single-marker analysis (ANOVA) and interval analysis (Mapmaker QTL). Most QTLs that were identified were associated with root thickn ess, root/shoot ratio, and root dry weight per tiller, and only a few with deep root weight. None were reliably associated with maximum root depth due to genotype-by-experiment interaction. Root thickness and r oot dry weight per tiller were the characters found to be the least in fluenced by environmental differences between greenhouse runs. Correla tions of root parameters measured in greenhouse experiments with field drought avoidance/tolerance were significant but not highly predictiv e. Twelve of the fourteen chromosomal regions containing putative QTLs associated with field drought avoidance/tolerance also contained QTLs associated with root morphology. Thus, selecting for Moroberekan alle les at marker loci associated with the putative root QTLs identified i n this study may be an effective strategy for altering the root phenot ype of rice towards that commonly associated with drought-resistant cu ltivars.