Radiation induced variations in photoperiod-sensitivity, thermo-sensitivity and the number of days to heading in rice

Abstract

Radiation induced semi-dwarf mutants derived from five japonica type varieties of rice were studied with regard to their photoperiod-sensitivity, thermo-sensitivity and the number of days to heading. The experiment was carried out under the natural conditions at Taipei. The coefficient of photoperiod-sensitivity (T.D.M.) and thermo-sensitivity (byx. z and byz. x) as developed by Oka (1954) were estimated for the mutants in comparison with their original varieties. It was observed that these various physiological characters could be altered rather easily by mutations. Mutants showed wider ranges in both positive and negative directions than their original varieties in all the physiological characters studied. Even though heading date depends on both photoperiod-sensitivity and thermo-sensitivity, it was estimated which of the two contributed more to the induced earliness in each mutant. This offers a basis for selecting early maturing lines of rice.