Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/1998
Publication Date: N/A
Interpretive Summary: Among the small grain cereal crops such as wheat, barley and rice it has been shown that erect rather than lax leaves and culms (stems) are associated with increased yield potential. This is believed to be at least partially due to less shading of lower leaves by the upper leaves, which allows them to capture more light energy and contribute more photosynthetic cproduct to the grain. Erect culms are also associated with decreased yield losses due to lodging. At the seedling stage however, more erect plants do not shade the ground as well as seedlings with more horizontal leaves. Since they do not inhibit the germination and growth of weeds as well, they suffer more yield losses due to weed competition. Extremely erect plants have leaves close together which can increase a plant's susceptibility to insects and diseases that are transmitted by leaf to leaf contact. Therefore, cereal breeders tend to select for an intermediate plant type, one having fairly erect leaves combined with a small tiller angle, so that the ground can be effectively shaded at the seedling state yet the leaf canopy remains open enough to decrease pest pressures and increase light penetration during grain fill. In China, there is a set of rice varieties noted for their high yield potential and rapid tillering and leaf expansion as seedlings. This study used progeny derived from a cross between a US rice variety and one of these high yielding Chinese varieties to identify a total of 12 genes for culm angle, flag leaf angle, and the angle of leaves below the flag leaf. These plant structure genes were mapped through their linkage with DNA markers. It is now possible to select and combine different genes through marker-assisted selection to create optimal plant architectures for a diverse range of target environments.
Technical Abstract: Plant type is an important composite trait associated with yield potential in rice and other cereal crops. Several characters associated with the plant type of modern rice cultivars including tiller angle, flag leaf angle, and the angle of leaves under the flag leaf were investigated using a complete linkage map with 115 well distributed RFLP markers and progeny testing of 2418 F2-derived F4 lines from a cross between O. sativa ssp. Japonica cv. 'Lemont' and spp. indica cv. 'Teqing'. Twelve quantitative trait loci (QTLs) were found to be responsible for the tremendous variation of three plant type characters in the Lemont/Teqing F2 population. One of these loci individually accounted for 47.5 percent of the observed phenotypic variation for tiller angle. This gene, named here as Ta, was located between RZ228 and RG667 on chromosome 9 and was also found to impact leaf angle. This major gene plus four QTLs accounted for 69.1 percent of the genotypic variation in tiller angle. Eight additional QTLs for leaf and flag leaf angles were also identified, which collectively explained 52.0 and 66.4 percent of the genotypic variation of these traits. Ta and three QTLs (Qfla2, QFla5 and QGla7) apparently affected the related plant type characters differently, suggesting their possible differential expression in different developmental stages of rice plants or possibly clustering of different genes affecting these traits. Plant type, and consequently grain yield of rice, may be improved by deliberately manipulating these QTLs in a marker-assisted selection program.