Effects of Gibberellin on the Morphogenesis in Rice Plants : 8. Effects on the spikelet formation in a special variety of paddy rice "Akaho"

Abstract

1. Studies on the effects of gibberellin on the spikelet formation were carried out in 1965 and 1966 years, using a special variety of paddy rice Akaho which has a genetic character to manifest various abnormalities in spikelets even under the usual cultivating conditions. Gibberellin was applied at the stage just before the panicle differentiation, at the concentration of 100 ppm mixed in the nutrient solution. 2. The symptoms of abnormalities in the control spikelets varied considerably by year and the expression of genetic character on the spikelet formation was seemed to vary according to the environmental factors. 3. Since almost all kinds of the spikelet abnormalities were promoted by the treatment, the physiological conditions caused by the exogenous gibberellin were considered to be quite similar with those induced by the genetic factors concerned with the abnormal formation of spikelets. 4. Though the number of spikelet organs was increased as seen in other varieties, the development of primary branches and spikelets in a panicle was decreased remarkably by the treatment in Akaho. The latter part of above results was different from what were obtained in the previous experiments on other varieties that every organs in the panicles had been promoted by the exogenous gibberellin. So, the optimum concentration of exogenous gibberellin should vary with the kind of organs or the varietal factors. 5. From the facts that the development of morphologically perfect stamens in a spikelet changes from two to eight in number by spikelet and the percentages of spikelets which have stamens more than or less than six in number increase conspicuously, the exogenous gibberellin is thought to make the physiological conditions very unstable and variable in a panicle by locus. 6. Frequent occurrence of the slightly feminish Intermediate organs and the increment of pistils per a spikelet in number give the impression that the exogenous gibberellin promotes the female tendency in Akaho, making a rather contrast to that obtained from the previous experiments on other varieties. The above results indicate that the effect of gibberellin on the sex expression may not be specific to the male or female but vary with the internal and external factors. 7. Some considerations were tried on the development of intermediate organs and the appearance of multi-stigmatic pistils and several conflicting phenomena obtained in this and the previous studies were indicated deferring. the decision of the question to the future investigations.