Toshinori Fukuyama

Variations of the vascular bundle system in Asian rice cultivars

SummaryThe capacity of vascular bundle system transporting assimilates from source to sink is one of the limiting factors for rice (Oryza sativa L.) yield. Genetic variation in vascular bundle system should be investigated for improvement of transporting efficiency. A total of 531 Asian rice cultivars were studied for vascular bundles in the peduncle and its relation to spike morphology. A few difference was detected for the number of primary rachis branches of the spike among the cultivars from various countries. However, the number of vascular bundles significantly differed among the cultivars; those from Nepal, Bangladesh and India bore more vascular bundles than those from Japan. Therefore, the ratio of vascular bundles to rachis branches (V/R ratio) was nearly 1.0 in cultivars from Japan, while those from Nepal, Bangladesh and India ranged from 1.3 to 2.2. Chinese and Indonesian cultivars incuded two types of high and low V/R ratios. Cultivars with high V/R ratio showed positive reactions to the phenol solution, while those with low V/R ratio were negative reactions, suggesting that the former cultivars are of Indica type and the latter of Japonica type. It was concluded that the relationship between vascular bundles and rachis branches differentiated among the ecotypes of Asian cultivated rice.

Variation of the vascular bundle system in Asian wild rice, Oryza rufipogon and its relationship to rachis branch number and growth habit

Accessions of Asian wild rice, Oryza rufipogonGriff., vary in phenology, growth habit, reproductivesystem, panicle architecture and rachis branchnumbers, and in habitat preferences. In this paper 86accessions of annual, perennial and intermediategrowth habit variants have been examined for variationin the numbers of rachis branches in the panicle andvascular bundles in their subtending peduncles.Accessions of annual habit, which regenerate from seedand are adapted to shallow and temporary swamps,developed fewer rachis branches (mean = 6.0) thanthose of perennial habit (mean = 7.2) which largelyregenerate vegetatively and are adapted to stable deepwater habits. In both cases variation within growthhabit groupings was narrow. Variation in vascularbundle numbers, which has not been previouslyreported, was similar (10.1 to 10.3), but morevariable within annuals. As a result the V/R ratio (ofvascular bundles: rachis branches) was higher inannuals (mean = 1.71) than among perennials (mean =1.46). Accessions of annual habit, and adaptedto a wide range of habitats, varied considerably inboth rachis branch (mean = 9.5) and vascular bundlenumbers (mean = 14.0), with V/R ratios similar tothose of perennial growth habit (mean = 1.49).Corresponding measures for both indica and japonica of cultivated rice (O. sativa) variednarrowly and were substantially greater for bothrachis branches (mean = 11.6 and 13.8, respectively)and vascular bundles (mean = 19.1 and 14.8,respectively), with V/R ratios of 1.67 for indica and similar to accessions of O.rufipogon of annual habit, and 1.07 for japonica and lower than accessions of O.rufipogon of both perennial and intermediate habit.Accessions of O. rufipogon from the India andIndochina regions were significantly lower in rachisbranch, but not vascular bundle numbers thanaccessions from China; with the V/R ratio higher amongaccessions from India than found in other geographicregions of origin. The possible role of O.rufipogon accessions of intermediate growth habit inthe evolution of cultivated rice is discussed,although it is speculated that accessions ofintermediate habit with high numbers of rachisbranches and vascular bundles may have resulted frominterspecific hybridization with O. sativacultivars.