Planting density and selection method in rice plant

Abstract

1. An investigation was made on the interaction between genotype and planting density in rice -plant, with the aim of contributing to the breeding of varieties adapted to high planting density. 2. The experiment consisted of two different forms of culture, i. e., early season culture and ordinary season culture. In early season culture ten varieties were used which were randomly chosen from the leading varieties in T5hoku District and in ordinary season culture again ten varieties from those in Chilgoku District (Okayama and Hiroshima Prefectures). The materials were grown under three different planting densities, i, e., 30cmX30cm, 2lcmX2lcm, 15cmX15cm, in a split plot design of 3 replications. The characters examined were culm length, panicle length, number of panicles, panicle weight per plant (yield), panicle weight per stem and heading date. 3. Mean values of the characters investigated decreased, as planting density increased, except culm length in. ordinary season culture which, on the contrary, increased. The effect of planting, density on the mean values was not the same fcr early and ordinary season cultures, varying with character. Analysis of variance indicated a significant interaction between genotype and planting, density in several characters such as yield and number of panicles. 4. The heritability estimates of various characters generally decreased as planting density increased, except that of culm length which showed an increasing tendency. 5. Since the heritability was generally higher in low plahting density than in high planting density, the genetic gain in high planting density from the selection in low density was examined, using the following formula (Falconer, 1960) (CRY)/(RY)=rA(ix)/(iY)(hX)/(hY) This examination showed that the selection for number of panicles is more effective when conducted in low density than in high density. In other characters, however, the indirect selection was cosidered not necessarily advantageous to the direct selection in high density, taking into account other facters such as sampling error and natural selection in breeding processes. 6. Summing up all the results it was concluded that the best method fcr breeding varieties adapted to high planting density may be F3 derived line method, or bulk method in which the breeding materials are grown in low planting density until around F5 in order to minimize the effects of competition and then selection is conducted in high planting density on the basis of line means.