2000 Volume 44 Issue 2 Pages 77-86
An attempt was made to determine the plant type of some high-yielding semidwarf Indica and Japonica-Indica hybrid varieties cultivated under the same conditions for two years, based on HOSHINO'S plant type index (PTI) and to improve the PTI to compare quantitatively their plant types mainly with those of Japanese varieties. HOSHINO'S PTI is based on the formula, PTI (HOSHINO) = [weight of one panicle (hereafter refered to as ‘panicle weight’) /number of panicles per plant] × 100. However, the percentage of filled grains led to larger fluctuations of the panicle weight which eventually became associated with relatively larger yearly fluctuations of the values. The term ‘potential yield of one panicle’ (hereafter referred to as ‘potential panicle yield’) instead of weight of one panicle was used to improve HOSHINO'S PTI. Potential panicle yield was expressed as [the number of spikelets per panicle × 1000-grain weight (brown rice) /1000] . As a result, the improved PTI= (Potential panicle yield/number of panicles per plant) × 100. Compared with the weight of one panicle, the yearly fluctuations of the potential panicle yield decreased markedly, especially in Indica and Japonica-Indica hybrid varieties which resulted in lower fluctuations of the improved PTI (IPTI) values. Therefore, the IPTI could be used more effectively for the determination of the plant type in a wide range of rice varieties. The IPTI values of the varieties ranged from 6.3-27.7 in 1995 and 7.7-31.0 in 1996, and the varieties were classified into three groups based on these values, i.e. category I (IPTI 25 or more), category II (15-21) and category III (13 or less) . Varieties in categories I and III were considered to belong the panicle weight type and panicle number type, respectively. Hieri, Norm 22 and all the other Japanese varieties (Nakateshinsenbon, Kinmaze, Nipponbare, and Koganenishiki) belonged to the categories I, II and III, respectively. The IPTI values of the high-yielding semidwarf Indica varieties showed large differences and they were classified into categories I (Gui zhao 2), II (BR3) and III (IR36), while the high-yielding Japonica-Indica hybrid varieties (Milyang 23, Suweon 258) belonged to category II. These high-yielding varieties showed higher IPTI values in comparison with the Japonica varieties with a similar tillering ability, due to their superiority in potential panicle yield owing to the larger number of spikelets per panicle.
