Application of Mendelian genetics in rice breeding

Abstract

The application of Mendelian genetics has clearly led to many breeding advances in rice as well as in other crops. We emphasize economically important traits for which segregation ratios can be distinguished without elaborate progeny testing or molecular markers. Four general groups of traits are reviewed: agronomic and physiological traits, grain quality, pest resistance, and resistance to abiotic stresses. The single most important trait has been semidwarfism, conferred by the sd1 gene. Other important agronomic and physiological traits are photoperiod sensitivity, glabrous hulls, gold hull color, and purple leaf. Among grain quality characters, amylose content is the most important, ranging from waxy types with essentially no amylose, to temperate japonica short - and medium-grain types with 16-18% amylose, to tropical japonica long grains with 21-24% amylose, and to many indica types with up to 28% amylose. Another significant grain quality trait is aroma, which often appears to be under simple gene ic control but which is difficult to recover in high-yielding backgrounds. Breeding for pest resistance, including both diseases and insects, has been one of the most successful examples of the use of major genes in crops, and yet it is a recurring challenge. The most important disease example is blast resistance, which has been a focus of breeding efforts for decades. The exploitation of major genes for bacterial blight resistance has been more successful than for blast. Many successful cases of major gene resistance for brown planthopper, green leafhopper, and gall midge have been reported in the past three decades. In general, resistance to abiotic stresses has been polygenic. Exceptions have been low-temperature-induced chlorosis at the seedling stage and submergence tolerance.