Studies on lodging in rice plants. I. A general observation on lodged rice culms.

A general observation was conducted on lodged rice culms in cultivars Sasanishiki and Koshihikari grown in paddy fields in 1986, 1987, and 1989. The shape of the cross section of internodes was observed to be not circular, but elliptical with a major and a minor axis. Flattening of internode calculated based on the difference between the major and minor axis was higher in lodged culms than in unlodged ones in the lower internodes. Values of the major and minor axis, which reflect the width of internodes, were lower in lodged culms, also, lengths of the lower internodes were longer than unlodged ones. The broken internode was found to be mainly the IV internode in Sasanishiki and IV, V internodes in Koshihikari. The breaking position in the broken internode was restricted to the portion ranging from 10 to 30% of the full internode length distant from the lower node level. This 20% portion was regarded as a breaking area of the broken internode. The breaking direction was observed to be the minor axis of the cross section of the broken internode in most cases. These results suggested that lodging occurs in limited internodes and at a specialized position and direction.