Japanese Journal of Tropical Agriculture

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An experiment was conducted to clarify the effect of shading on the development of lateral branches and the ripening of racemes in castor plants.
The seeds of castor plants var. Shanghai were sown at 1.5m×1.5m intervals in a field at University of Tsukuba on June 11th, 1980. The experimental plots were; A) no treatment (control), B) shading with one layer of black cheesecloth (55-65% light intensity of control) and C) shading with two layers of black cheesecloth (30-39% light intensity of control) . The treatment began just before the flowering of the primary raceme. The length of the lateral branches were measured every three days after the flowering of the primary racemes. The plants were harvested on the twentieth day and the fortieth day after flowering, and were seperated into branches. The leaf area and the dry weight of each plant were measured.
The results were as follows:
1. It was shown that the uppermost branch on a main stem is dominant in development under any light intensity tested.
2. The development of lateral branches was reduced under low light intensities. The lower the light intensity, the stronger the inhibition of the development of lateral branches, and the lower the node of a lateral branch on a main stem, the stronger the inhibition of the development of lateral branches.
3. The seed yield of the primary raceme was decreased under low light intensities because of the decrease in the number of capsules and the weight of 100 seeds. The decrease in the number of capsules was especially great and was caused by the abscission of flowers and capsules.
4. A low light intensity inhibited the ripening of racemes more severely than the development of lateral branches. This fact is important in the cultivation of castor plants.

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Japonica varieties showed higher increasing rate with increasing supply of nitrogen in soluble and fraction 1 protein contents, photosynthetic activity and ratio of photosynthesis to respiration than indica varieties, resulting in higher efficiency of dry matter production in the former than in the latter. The relatively high efficiency of japonica varieties favored reproductive growth phases, such as effective tiller percent, yielding capacity-number of spikelets and fertilization, rather than vegetative growth, such as plant weight and expansion of leaf area, and resulted in distributing more dry matter into grains. Indica varieties behaved adversely and the increase of their grain weight was relatively low.

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