QTL ANALYSIS OF ABA PRODUCTION IN WHEAT AND MAIZE AND ASSOCIATED PHYSIOLOGICAL TRAITS

Abscisic acid (ABA) is known to affect many aspects of plant growth an d development, and stress-induced increases in tissue ABA content are thought to help the plant adapt to the stress. It is, therefore, of in terest to identify genes that regulate ABA production in a stressed pl ant. The possible consequences of allelic variation in these genes can be determined by comparison within genomes of quantitative trait loci (QTL). We have identified genotypes of wheat and maize that differ by up to threefold in ABA accumulation following a drought stress, A pop ulation of wheat plants derived from a cross between a high-ABA produc er (SQ1, an experimental line) and a low-ABA producer (Chinese Spring, a landrace) has been examined for drought-induced ABA production and genotyped for isozyme and restriction fragment length polymorphic (RFL P) markers. Leaf 4 was tested for drought-induced ABA production in 13 9 F-2 plants, which gave a range in leaf ABA contents from about 50 to 560 ng/g fresh weight. One-way analysis of variance showed significan t association between markers on the long arm of chromosome 5A and a Q TL regulating ABA production, the position of which was estimated usin g the Mapmaker-QTL computer program. An F-2 population of maize plants was characterized with 32 RFLP markers and used to locate genes regul ating ABA content in plants growing under drought conditions in a glas shouse. Several other physiological, morphological, and agronomic trai ts were also measured in these plants, and comparative QTL analysis al lowed some possible causal relationships between ABA and other stress- related traits to be tested. The results showed that leaf ABA was more likely to regulate stomatal conductance than xylem ABA, in contrast t o the recent findings of others. There was no evidence that ABA had an y effect on plant height or developmental rate. The value of this tech nique for testing the likely roles of ABA in a stressed plant is discu ssed.