Comparison of the excised seminal root growth between Japonica and Japonica-Indica hybrid rices under different components of culture media.

Abstract

In order to study the difference in the growth of excised seminal roots (root-tips) in vitro culture between Japonica and Japonica-Indica hybrid rices, different concentrations of sucrose, casamino acids (casein acid hydrolysate) or vitamins (thiamin, pyridoxin and nicotinic acid) in the culture medium were investigated. Effect of cultural temperature and degree of pH value of the medium on the excised seminal root growth were also tested. Unless otherwise mentioned, a Japonica rice cultivar (Nipponbare) and a Japonica-Indica hybrid rice cultivar (Milyang 30) were used as materials. All the experimental procedures were same with those described in the previous paper5). 1. Under the temperatures of 19° to 34°C, the excised seminal root growth of the Japonica-Indica hybrid rice was better than that of the Japonica rice (Fig. 1). 2. The optimum pH value of culture medium for the excised seminal root growth were 4.0 to 4.5 in the Japonica rice and 4.5 to 5.5 in the Japonica-Indica hybrid rice (Fig. 2). The optimum concentrations of sucrose for the root growth were 6 to 8% in the former and 4 to 6% in the latter (Table 1). On the other hand, effect of concentrations of vitamins on the root growth remained unclear in the both type of rices (Table 4). In all the culture media, however, the excised seminal root growth were better in the Japonica-Indica hybrid rice than in the Japonica rice. 3. In the Japonica rice, the excised seminal root grew well with increasing of concentration of casamino acids in the culture medium. On the other hand, in the Japonica-Indica hybrid rice, the dry root weight increased with increasing the concentration of casamino acids in the medium, while the main root length decreased with the casamino acids concentration (Table 2). When the excised seminal roots of each 20 cultivars of Japonica and Japonica-Indica hybrid rices were cultured in the medium containing 0% and 0.2% casamino acids, the root growth of all the Japonica rice cultivars and that of about one-third of Japonica-Indica hybrid rices were better in the 0.2% casamino acids medium than in 0% casamino acids. In the two-thirds of Japonica-Indica hybrid rices, however, the main root length was longer in the 0% casamino acids than in the 0.2% casamino acids, but the dry root weight was larger in the latter than in the former (Table 3). Thus, the effect of casamino acids on the excised seminal root growth clearly differed between the Japonica rice cultivars and the majority of the Japonica-Indica hybrid rices.