The elongation of mesocotyl and coleoptile plays important roles in the seedling emergence and stand establishment of dry direct-seeded rice. Experiments were carried out to elucidate the effects of seed-presoaking treatments of GA3 and some inorganic salts on the mesocotyl, and coleoptile elongation of rice. Seed-soaked GA3 promoted the elongation of mesocotyl, but little effect on the coleoptile elongation. The stimulation effects of GA3 were found to be enhanced by addition of CaCl2 However, the sole treatment of CaCl2 showed no stimulating effect on the mesocotyl and coleoptile elongation. Mesocotyl elongation was most prominent in the combined treatments of 50ppm GA3 with 100 mM CaCl2 . The synergistic effects of GA3 and CaCl2 on mesocotyl elongation varied with varietal groups. The stimulating effects of GA3 were enhanced significantly by the addition of CaCl2 in japonica varieties, Dongjinbyeo, Ilpumbyeo and Milyang 95, and tall indica variety, Labelle, but not in semidwarf Tongil type varieties, Tongilbyeo, Milyang 23, and Nampungbyeo, and semi-dwarf indica, Short Labelle. The promoting effects of GA3 on the mesocotyl elongation were decreased in proportion to the lowered osmotic potential by PEG 6000 on the contrary to CaCl2 This implies that the synergistic effects of CaCl2 with GA3 on mesocotyl elongation was not caused by osmotic potential lowered by CaCl2 addition but by the salt itself. Salts such as Ca(NO3 )2 , MgCl2 BaCl2 , NaCl, KCl and KNO3 showed the synergistic effects with GA3 on mesocotyl elongation as well. The degree of synergistic effects showed no differences among salts tested, implying that there is no specificity of ions constituting the salts.

Prediction of rice developmental stage is necessary for proper crop management and a prerequisite for growth simulation as well. The objectives of the present study were to find out the relationship between the plastochrone index(PI) and the developmental index(DVI) estimated by non-parametric phenology model which simulates the duration from seedling emergence(DVI=0) to heading(DVI=l) by employing daily mean air temperature and daylength as predictor variables, and to confirm the correspondency of developmental indice to panicle developmental stages based on this relationship. Four japonica rice cultivars, Kwanakbyeo, Sangpungbyeo, Dongjinbyeo, and Palgumbyeo which range from very early to very late in maturity, were grown by sowing directly in dry paddy field five times at an interval of two weeks. Data for seedling emergence, leaf appearance, differentiation stage of primary rachis branch and heading were collected. The non-parametric phenology model predicted well the duration from seedling emergence to heading with errors of less than three days in all sowings and cultivars. PI was calculated for every leaf appearance and related to the developmental index estimated for corresponding PI. The stepwise polynomial analysis produced highly significant square-rooted cubic or biquadratic equations depending on cultivars, and highly significant square-rooted biquadratic equation for pooled data across cultivars without any considerable reduction in accuracy compared to that for each cultivar. To confirm the applicability of this equation in predicting the panicle developmental stage, DVI at differentiation stage of primary rachis branch primordium was calculated by substituting PI with 82 corresponding to this stage, and the duration reaching this DVI from seedling emergence was estimated. The estimated duration revealed a good agreement with that observed in all sowings and cultivars. The deviations between the estimated and the observed were not greater than three days, and significant difference in accuracy was not found for predicting this developmental stage between those equations derived for each cultivar and for pooled data across all cultivars tested.