Abstract
This study was carried out to survey the way of chemical regulation of plumule growth of japonica rice when seeded deeply in direct sowing culture. The seeds of japonica rice, Oryza sativa L., var. Sasanishiki, were soaked in deionized water at 25°C for 2 days. The immersed seeds were air-dried on a filter paper for several minutes, and then coated with lanolin paste containing a mixture of 0.1% (w/w) abscisic acid (ABA) and gibberellic acid (GA3), or with lanolin proper as a control. The coated seeds were sown in soil-packed pots at the seeding depth of 0.7, 4 and 6 cm. No fertilizer was added to soil. These pots were kept in the growth chamber (30°C; white light from fluorescent lamps, 500 lx). In the case of the controls, the percentage of seedling emergence was only 36 in the deep (6 cm) seeding plot versus 100 in the shallow (0.7 cm) seeding ones. The emerged seedlings in the former plot showed the characteristic of etiolation, i.e. elongated internodes and yellow slender leaves, although its mesocotyl length was less than 3 mm. On the other hand, when treated with the 0.1% ABA and GA3 mixture the seedlings penetrated the soil by the vigorous mesocotyl growth until their coleoptilar tips experienced light, and developed non-etiolated leaves. As a result, the percentage of seedling emergence reached two times of control (fig. 1-2). To test the effect of the seed-coating on the successive growth and yield in a direct sowing culture, the coated seeds with or without a mixture of 0.1% ABA and GA3 were sown in soil-packed Wagner pots (1/5000a) at depth of 0.7 and 6 cm. Then they were allowed to grow in the open-air conditions till harvest. The tiller number in the deep sowing plot was much smaller than in the shallow one, whereas the treatment with a ABA and GA3 mixture increased the tiller number in the deep sowing plot. In this experiment, however, no significant differences among plots were found in grain yield (Table 1). In conclusion, these results suggest a possibility to regulate the plumule growth of rice seedlings in direct sowing culture by the seed-coating with a mixture of exogenous growth substances.
