Abstract
The variation of seedling growth, which may affect seedling salt tolerance, of 12 rice cultivars was examined based on the pattern of seedling fresh weight histogram. Some cultivars showed a normal distribution pattern while other cultivars exhibited an irregular or multimodal histogram. The variability in seedling growth histogram almost coincided with that in the embryo weight histogram. After one cycle of selection from a major peak in the seedling fresh weight histogram, the number of peaks in the seedling growth histogram of the next generation plants was considerably reduced. When seedling salt tolerance within the rice cultivar was studied (by growing one-week-old seedlings for 30 days under salinized and control culture solutions), the seedling dry weight histogram of the cultivar in salinized condition coincided well with that of the control. Larger seedling had higher relative weights under salinized conditions, lower sodium ion content, and lower Na/K ratio than smaller plants. Variability in seedling growth within a cultivar, therefore, would affect the quantitative evaluation of salt tolerance (e. g., survival ratio and growth rate) of rice seedling. The possibility of selecting salt-tolerant materials from a given cultivar was also examined. The results were not consistent because of various factors involved in establishing seedling salt tolerance. It is suggested that cultivars should be genetically purified first before they are used in salinity response studies.
