Physiological Studies on the Tolerance of Rice Plants to Salinity : Part 4. Effects of salinity on rooting activity of rice plants.

Abstract

With the purpose of finding some clue as to the relation between salt tolerance and rooting activity, the present study was using Oryza sativa L. var. Eiko as material. Plants were grown on sand cultures irrigated with either a basic nuturient solution (control) or basic nutrient plus 0.3 % NaCl. The experimental results obtained may be summarized as follows: (1) NaCl exhibits a slight tendency to cause decrease in root number, while no definite trends can be observed respecting top length, tiller number, new leaf formation and root length. (2) Fresh and dry weights of rice plants decreased as a result of the treatment with saline solution, particularly root weight was seriously affected. Such salt treatment resulted in a decrease of rice yield by 28.8 %. (3) Leaf withering due to the salt treatment was significant at earlier growing stages, followed by a gradual depression toward later stages; it decreased to a minimum during ear-forming stage which coincided with the maximum tillering stage in Hokkaido. These results suggest that the tolerance of rice plants to salinity is maximum during the ear-forming stage. (4) Rooting activity of rice plants decreased when treated with saline solution. Trends foward increase in length, number, amount (length × number) and dry weight of new roots were recognized toward the ear-forming stage. These facts suggest the assumption that the rooting activity of rice plants is closely associated with their salt tolerance. (5) Ratio of rooting (new root dry weight/top dry weight × 100) was decreased by the treatment with salt solution, however, there is left some room to associated this response directly with the salt tolerance.