Rice Genetics IV - IRRI books - International Rice Research Institute

Elongated uppermost internodeA gene for elongated uppermost internode (eui), which produces a doubling in lengthof the uppermost internode, was described by Rutger and Carnahan (1981). The euiwas proposed by the authors for use in the pollen parent in hybrid rice seed production.There would be obvious advantages to having a taller male parent in crossingfields and the resulting F 1 , being recessive, is semidwarf like the female parent. Althoughpatented, the eui stocks were distributed freely to requesting breeders. A useunforeseen by Rutger and Carnahan (1981) was that of putting the eui gene into thefemale parent in order to get the panicle above the leaf sheath (Zongtan and Zuhua1989). This would then eliminate the need for gibberellin treatment of females in seedproduction fields. As far as is known, use of eui in either male or female seed parentshas not been practiced on any significant scale.Grain qualityAmylose contentAmylose content is the single most important criterion of cooking quality in rice.Waxy (wx) rice varieties have near zero amylose in endosperm starch. Such waxy orglutinous rice varieties are prized for pastries and ceremonial foods. Many waxy varietiesare known in world collections, especially in short-grain temperate japonicarice. The waxy varieties are usually lower yielding than standard varieties, but this isoffset by the higher prices for waxy grain. Typical was the experience with MochiGomi in the U.S., which was valued for its waxy grain even though it was tall andlow-yielding. A clever use was made of induced mutation by Carnahan et al (1979) todevelop variety Calmochi-201 in the otherwise well-adapted, high-yielding varietyS6. Many waxy varieties are known in world collections, especially in short-graintemperate japonica rice and long-grain indica rice from Southeast Asia. RD6 is apopular rice variety from Thailand that is a waxy mutant of Khao Dawk Mali 105.Niaw San Patang used to be the most popular waxy variety in Thailand and is reportedlya waxy mutant of Leuang Yai 148.Since the waxy rice markets are somewhat limited, greater emphasis has beengiven to inheritance of other amylose levels, including low amylose (16–18%) contentas in temperate japonica short- and medium-grain rice, intermediate amylose(21–24%) as in the tropical japonica long grains of the southern U.S., and high amylose(26–28%) of older indicas. In crosses between low amylose and intermediateamylose parents, amylose content was usually controlled by one or two genes (Stansel1965, Bollich and Webb 1973, McKenzie and Rutger 1983, Kumar and Khush 1987).In crosses with high-amylose parents, genes for high amylose were dominant overthose for low or intermediate levels (Kumar and Khush 1987). In addition to themajor genes, minor genes are usually present.Additional genes affecting starch composition have been identified in japonicagermplasm (Yano et al 1988) and transferred to an indica background by backcrossing(Kaushik and Khush 1991). As far as can be determined, these genes—for sugary,shrunken, floury, white core, amylose extender, and dull endosperm—have not yetbeen used in variety development.Application of Mendelian genetics in rice breeding 31