Abstract: In this study, the change of endogenous hormones in reciprocal fourth leaf of cotton plant after topping was researched by carrying out the plot experiments, and the effect of topping on cotton yield and quality was analyzed. The results are as follows: ① After topping, the ratios of IAA, CTK, GA3 and ABA in reciprocal fourth leaf of cotton plant within a certain period of time were decreased, and the ABA concentration was significantly increased; ② After topping, the ratios of IAA, CTK, GA3 and ABA in reciprocal fourth leaf of cotton plant could be increased by daubing NAA, and the content of ABA in reciprocal fourth leaf of cotton plant could be maintained; ③ After topping, the content of chlorophyll and the disease index of reciprocal fourth leaf of cotton plant were significantly higher than that without topping, and the ageing process of cotton leaves could be slowed down by using NAA externally; ④ The exfoliation rates of cotton buds and bolls could be reduced after topping. The cotton bolls and buds grew mainly on the lower and central parts of cotton stem, but the preponderance of boll setting and bolls on upper branches was not significant; ⑤ The difference of cotton yield and quality among the situations after topping, without topping and by daubing NAA after topping was not significant, but three was a potentiality to increase cotton yield under the treatments of taking improved variety, applying fertilizer, hormone and inhibitor, enhancing management, etc.

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