Tohoku Journal of Crop Science

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Influence of the temperature treatments before and after the growth stage of panicle formation on the number of spikelets per panicle and the sterility of grains were examined under the controled environments for several rice cultivars which had different local adaptability. The results obtained are summerized as follows : 1. Plant height was increased in every cultivar as the temperature (of the growth period) before the panicle formation stage increased. The increasing rate in Shiokari, cultivar adapted to cold district of Japan, was twice as high as that in Harima, cultivar adapted to the warm district of Japan, under the high temperature condition. Number of tillers, on the contraly, decreased in accordance with the increase in temperature in each cultivar. Among those the rate of depression in high temperature was remarkable in Harima. 2. Number of spikelets attached on the primary rachis-branches was increased by the high temperature treatment in the growth period prior to the panicle formation satge in each cultivar. The efect of any temperature treatment after the panicle formation stage on it was not recognized. 3. As the temperature in the growth period before the panicle formation stage increased, the sterility of grains was decreased in Shiokari. In the cultivar Harima, however, the sterility of grains decreased with decreasing temperature. 4. Difference in number of spikelets per panicle by the differential temperature treatments was governed primarily by the difference in the number of degenarated secondary rachis-branches caused by the treatments. 5. It was recognized that the low temperature treatment in the growth period after the panicle formation stage did not result in the increase in sterility of grains, but the treatment brought about the increase in the number of the degenerated secondary rachis-bran-ches in Shiokari which has been considered to be one of the cold tolerant varieties cultivated in the northeastern cold district of Japan.

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The effect of ear barrenness on concentration of total available carbohydrates (TAC) in stalks of a two-ear type hybrid, Hokuyu, was examined. Fertilization was prevented by placing waxed paper bags over the ear shoots of the first ear, the second ear, and the both ears before silking, as shown in Fig. 1. The concentration of TAC in the stalks with the barren ear or ears increased markedly because of absence or decrease of storage organ for the carbohydrates produced after flowering (Fig. 2). In the plant with one barren and one normal ears, a higher TAC concentration was observed at the nearest internode to the barren ear three weeks after silking (Fig. 3).

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The relationships between grain yield and cross-sectional area of stalks (CSA) were studied using the data from a hybrid, Tomorokoshi Koh No. 7,planted at various populations on the soils of different fertility levels (Table). The logarithms for yield per CSA decreased linearly as the CSA per land area was increased and there was a high correlation coefficient betwen them. Using the linear relationship, a yield-CSA curve was determined. The formulae for the relationship are expressed by equations as follows : log y=log K+bS or y=K·10^bS Y=yS=SK·10^bS Where y is the yield per CSA, K is the constant, b is the regression coefficient, S is CSA per land area and Y is the yield per 10a. If the latter equation is differentiated with respect to S and the result equated to zero and solve for S, the result is : S^opt=-1/2.303^b Where S^opt is the CSA that will give the maximum yield. The method above mentioned is assumed to be very useful and convenient for predicting yield since stalk-diameter attains at earier stage before silking and only two yield-CSA values are needed regardless plant populations.

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Growth responses of alfalfa plants to temperatures combined with light-intensity and air-humidity were tested. Plant height, branch number, leaf number and total dry weight were greater under strong light and high-humidity than under weak-light and low-humidity, respectively. The optimum temperature for dry matter production was 25/20°C or 20/15°C. Top/root ratios were higher under weak-light, hight-humidity and high temperature compared with the respective opposite conditions. Nitrogen accumulation had a strong correlation with dry matter production (r=0,988), showing 35 mg increase in dry matter per lmg nitrogen increment. TAC accumulation of whole plant was greatest at 20/15°C, and that of stubble and roots was greater under strong-light and low-humidity, predicting a better regrowth under these conditions.

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