J Integr Plant Biol. ›› 1956, Vol. 5 ›› Issue (2): -.

• Research Articles •    

The Effect of Light Intensity on Bud and Boll Shedding of Cotton Plant

C. C. King, T. S. Ni, Y. W. Tang, C. W. Cheng, C. L. Chang, S. F. Lui, W. Y. Lui and S. G. Lee   

Abstract: There are a number of external factors which cause the physiological shedding of buds and bolls of cotton plant. It is, however, suggested that under different environmental conditions, the factors which affect the dropping most are quite different. In a preliminary experiment we found that under the condition of excessive growth of cotton plant, the low light intensity was the principal factor in the heavy shedding of buds and bolls. In an endeavour to investigate the effect of different light intensity on the dropping of buds and bolls at different growth periods and to reveal the physiological mechanism of shedding, a series of experiments were performed. The results are given as follows: First of all, we found that the lower the light intensity was, the higher the percentage of shedding would be. The dropping of buds and bolls was 100 % when the light intensity on the top of cotton plant was reduced to one twentieth of sunlight by means of a shade. Heavy shedding was induced from the beginning of bud formation to the stage of 50% flowering by low light intensity, and the percentage of shedding was found to the 90% even under the intensity of one fourth to one fifth of the sunlight. Low light intensity delayed the formation of buds and altered their characteristic of shedding with regard to their relative positions on the fruit branches. Furthermore, it was found that the lower the light intensity was, the younger the shed buds would be. Although the dropping of bolls was increased by low light intensity, yet the correlation between the age of the boll and its shedding remained unchanged even under the lowest light intensity. In addition, it was found that none of the bolls at the ago of l0 days shed under low light intensity. Dealing with the metabolic changes within plant, we found a change in the proportion of different types of organic food substances because of the reduction of the light intensity and as a result of the overgrowth of the vegetative part a decrease in available organic food for the reproductive organ occurred, hence the heavy shedding of buds and bolls. It frequently happened that the vegetative growth was exuberant when the supply of water and fertilizers was sufficient. As a result of the overlapping of the branches and leaf blades, the light intensity in the cotton field was very low especially under the condition of high density of crop. Low light intensity is, therefore, the principal factor of heavy shedding, and the effect of ventilation is of secondary importance The heavy dropping of valuable buds and bolls at the middle and lower parts of cotton plant occurred under the condition mentioned above. Thus, not only was the period of harvest delayed but also the yield and the quality of fibres were decreased. In order to improve the light condition in the cotton field, the following points of agricultural technique are recommended: (1) to pinch the plants together with proper defoliation; (2) to adopt a rational density of crop; (3) to change the spacing and to plant in square and (4) to breed new types of cotton with short branches.

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