Report of the Chugoku Branch of the Crop Science Society of Japan

Six rice varieties were grown in saline soil to analyze varietal difference in salt tolerance at the reproductive stage. Grain yield decreased with NaCl concentration in all varieties. In IR28 (salt-sensitive), Nipponbare, Akenohoshi and Akebono, the decrease resulted from the reduced panicle number, number of grains per panicle and one-grain weight. However, in IR4595-4-1-13 (IR4595) and Kala-Rata 1-24 (KR1), both salt-tolerant, the decrease was due to the reduced panicle number and one-grain weight only. IR4595 and KR1 showed relatively low leaf-Na content on any leaf position. IR28 and Japanese varieties had high Na content in the most active leaves at the panicle formation stage. The number of grains per panicle was negatively correlated with the Na content as remarkably exemplified in IR28. The decrease in one-grain weight was negatively correlated with Na content of the first internode. IR4595 and KR1 had high Na content in the first internode at high NaCl treatment, hence, reduced one-grain weight.

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An assimilation chamber for simultaneous measurement of photosynthesis, respiration and transpiration of intact plant was set up, and its function was examined especially inmeasuring root respiration and estimating dry matter increase by measured CO_2 exchange rate. Rice seedlings grown at different nutrient conditions were used as plant materials. Well-controlled pH and temperature of nutrient solution made possible a stable and continuous measurement of root respiration using an infrared gas analyzer. Dry matter increase calculated by CO_2 exchange rate was a good estimate of the measured value. There was positive correlation between top dry matter partitioning ratio and relative value of top respiration rate, and between top-root dry matter partitioning ratio and top-root respiration ratio. Therefore, the assimilation chamber was evaluated to be of help for the analysis of physiological dynamics in the growing plant.

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To clarify the influence of sowing times on seed production, soybean cultivars 'Tamahomare' was sown at 1 week interval, from June 4 to July 23, in 1982 and 1986. The number of nodes in main stem decreased with delay of sowing time from June 4 to June 25, but there was little difference in sowing from June 25 to July 16. On the other hand, the number of branches and total nodes per plant decreased with delay of sowing time. Especially the decrease of branches in soybeans sown in July was remarkable. The seed yield per unit area was correlated with ripened pod number per unit area. As the number of nodes and branches were greater, the number of ripened pods increased. In sowing from early to middle June, grain/stem ratio was low, due to both of high death rate of branches and low podding rate on lower-nodal-position branches. On the other hand, in sowing from middle to late July 100 seed weight tended to be low, because of short ripening period. Therefore, it was suggested that an optimum sowing time of a medium type cultivar 'Tamahomare' is from late June to ealy July in Sanyo districts.

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