Internode elongation of the rice culm begins almost simultaneously with the change from the vegetative phase to the reproductive phase. Although this synchronism suggests the existence of an interaction between the panicle development and culm internode elongation, little information is available about panicle and internode interaction. In this study, we examined 18 mutants from cv. Taichung 65 that were defective in panicle and/or spikelet development. The 18 mutants were classified into three groups by the organ in which the major mutant phenotypes were observed; (1) mutants with aberrant rachis/branches, (2) mutants with aberrant spikelets/flowers, (3) mutants with aberration in both rachis and spikelets. Most of the mutants with aberrant rachis/branches showed an abnormal culm elongation. In contrast, those defective in only spikelet development showed an almost normal culm elongation. The correlation analysis showed that panicle traits were significantly correlated with the length of the distal one or two internodes. Principal component analysis of the culm internode length showed that the mutants defective in rachis/branch development were positioned far from the wild type, while those with normal panicles and aberrant spikelets were distributed near the wild type. These analyses revealed that culm elongation, especially for the upper internodes, was affected by the early developmental mode of panicles. Although the mechanism by which panicle development regulates the elongation of upper internodes has not yet been identified, the present study indicates that the elucidation of early panicle development is essential for a comprehensive understanding of culm internode elongation.
2003 by JAPANESE SOCIETY OF BREEDING