EFFECTS OF DEEP-WATER TREATMENT ON THE GR OWTH OF CULMS AND THE LODGING RESISTANCE IN JAPONICA TYPE PADDY RICE (ORYZA-SATIVA L) CULTIVARS

We carried out this experiment to clarify the growth of culms of Japon ica type rice cultivars under deep water conditions with special refer ence to lodging resistance of culms. We used four Japonica type paddy rice cultivars which are different in plant type. Plant types of Nippo nbare and Sasanishiki are high tillering type, and Koganenishiki and T sukinohikari are ear weight type. Deep water treatment was starred fro m the time of the 8th leaf emergence in main stem and was kept to the ripening stage. The water depth (about 25 cm) was deep enough to subme rge the sheath of the 7th leaf of the main stem. In the deep water plo t at the ripening stage, the diameter of all the cultivars was remarka bly large and the breaking strength of the basal elongated internodes tended to increase. However, the breaking strength of the deep water p lot was inferior to that of the control plot when the internode was th e same diameter as the control plot. In the deep water plot, remarkabl e development of lysigenous aerenchyma, with a diameter as much as 3.5 times that of the control plot, was observed and the occupation ratio of lysigenous aerenchymas in the cross section of elongated internode s was about 13.7% while in the control it was about 1.5%. The remarkab le development of lysigenous aerenchyma may be one of the structural a daptations to aquatic conditions and may play an important role as a p assage of air. However, this structural adaptation caused the elongate d internode tissue to become insufficient by remarkable development of lysigenous aerenchyma, and this led to a decline in the contribution of the thickening of the basal elongated internode to the breaking str ength.