Genetic Control for Leaf Photosynthesis in Rice, Oryza sativa L.

Inheritance of leaf photosynthesis in rice and relationships between leaf photosynthesis and various characters were studied with infrared analysis of net C02 exchange method in a cross experiment between Japanese variety Nakate Shinsenbon(P1) and USA variety CP-SLO (P2) F1 mean for leaf photosynthesis in terms of apparent photosynthesis (Pa) was very close to P1 that was the low parent in Pa. F2 segregation in Pa distributed in a wide range from P2 to even lower than P1 Moreover, a bimodal distribution, one mode corresponding to P1 with a predominant number of plants and the other mode corresponding to P2 with much less plants, was clearly established. Hence, we concluded that the expression of leaf photosynthesis would be controlled by single major gene and that low leaf photosynthesis is dominant. Pa significantly correlated negatively with specific leaf area and positively with leaf areal nitrogen content in F2 progeny. Significant partial correlation existed only between Pa and leaf areal nitrogen content, indicating that areal nitrogen content is the major factor associating with Pa. Still, other undetected factors are indicated to be equally involved in the expression of Pa. In F2 progeny, Pa did not correlate with days to heading, culm length, panicle length and length/width ratio of grain. It neither correlated with some characters controlled by single major gene such as esterase isozyme, apiculus color, awn presence, and blade pubescence, indicating that gene(s) controlling Pa may not link with any of them. Besides, a possible effective introduction of glabrous habit into Japanese rice was demonstrated by the absence of any signiflcant difference in seven agronomic characters between glabrous and pubescent F2 plants. In conclusion, with its rather simple manner of inheritance and its independency from various agronomic characters, leaf photosynthesis can possibly be increased by inten-tional selection in future rice breeding.