Isolation and applied genetic study of rice mutant genes controlling the internode elongation pattern.

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Rice culm is consisted of some elongated internodes and these relative length ratios to culm are under genetic control. Such characteristics is so-called ‘internode elongation pattern' and it is an important agronomic trait because that not only the culm length but also the difference of such pattern are involvement in lodging resistance of rice plant. So many dwarf or semi-dwarf genes were known to regulate the culm and internode elongations.We have detected some dwarf or semi-dwarf genes by map-based cloning and examined the effects of these genes action on culm and internode elongation pattern. The results are as follows.1.sd1 which is loss of function in gibberellin biosynthetic enzyme gene, GA20 oxidase (GA20ox-2) reduced culm elongation but internode elongation pattern and panicle elongation were not different from those of wild type.2.d35 encoding the gibberellin biosynthesis enzyme gene, ent-kaurene oxidase also reduced the culm elongation. However, in d35 mutant, the upper side internodes of culm and panicle were relatively reduced more intensely and thus the effect of d35 mutation on lodging resistance was lower than that of sd1.3.d2 and d61 are a loss of function in brassinosteroid biosynthesis and perception respectively, and these mild mutations had elected leaves and reduced relatively the lower side internodes of culm, resulting the higher lodging resistance. However, the effect of these mutant genes was thought to be inadequate for the use as a practical semi-dwarf gene because of the negative effect to grain yield.4.A series of our studies in d61 of rice contributed the isolation of barley's practical semi-dwarf gene, ‘uz'.