Studies on the Effects of a Cool Water Treatment on the Appearance of Abnormal Spikelets in a Special Variety of Paddy Rice "Akaho"

Abstract

Studies on the morphogenetic effects of a cool water treatment on the spikelet formation were conducted with a special variety of paddy rice Akaho. A cool water irrigation had been known to induce abnormal spikelets even in the common varieties and also the Akaho of special variety had been found by Dr. KASAHARA to have genetic characteristics to express abnormal spikelets even under usual cultivating conditions. From the results obtained in this and Dr. KASAHARA's experiments, the physiological condition in the apical meristem of spikelet in Akaho was considered to be very unstable genetically in regard to the morphogenetic regulation of spikelet, bringing about various abnormalities in the inception and development of organs easily by a trifling disorder of physiology in spikelet primordium. Since a cool water treatment (13-15°C) which was applied at the stage of spikelet primordium differentiation was found to promote the appearance of abnormal spikelets in Akaho greatly, it was considered that the physiological changes caused by a cool water treatment may be similar to those which happen when abnormality is expressed as an inherited character in Akaho under usual cultivating conditions. It was also found that a cool water treatment affected sex expression and promoted the female tendency, suppressing the male one. The number of stamens decreases and the development of pistilate organs becomes vigorous in the plot of treatment. The differentiation and branching of vascular bundles in the process of spikelet formation seemed to be improved by the cool water treatment, resulting in the increase of glumes in number and frequent appearance of spikelets with multi-florets or ovaries. These phenomena of modification of sex expression and promotion of vascular differentiation mentioned above, may be interesting subjects to be investigated from the aspect of the changes in level of some endogenous growth substances which are caused by a cool water treatment.