Objective Relationship between the endogenous hormones, enzyme activities, and fruit cracking of wax apples was investigated.

Method Two varieties of wax apples, the fruit cracking-resistant ‘Zihong’ and the fruit cracking-susceptible ‘Fenhongzhong’, were compared on fruit growth and appearance. Variation in endogenous hormone contents in pulp and peel as well as cell-wall metabolism-related enzyme activities in the fruits of the cultivars were analyzed.

Result Dimensions of the developing fruits of Fenhongzhong were consistently significantly smaller than those of Zihong. In 30-40 d after full bloom, Fenhongzhong underwent rapid fruit enlargement. From the 30^th to the 50^th day, the shape indices decreased gradually with the transverse diameter extending faster than the longitudinal diameter. In 50 d, the contents of GA, IAA, and ZT in the peel and the (GA+IAA+ZT)/ABA ratio in the pulp and peel became significantly or extremely significantly higher than those of Zihong, but the ABA content in the pulp and peel significantly or extremely significantly lower. The PPO activity in the peel was significantly or extremely significantly higher than that of Zihong in 30 d and 50 d, while the POD activity in the pulp extremely significantly or significantly higher in 40 d and 50 d.

Conclusion Fenhongzhong wax apple fruits had relatively low indicators on the shape. During the mid to late stages, the fruits grew faster transversally than longitudinally. The relatively high content of growth-promoting hormones, i.e., GA, IAA, and ZT, particularly in the peel, low ABA content, high (GA+IAA+ZT)/ABA ratio, high PPO activity in the peel, and high POD activity in the pulp in late developmental stages all seemed to contribute to fruit cracking tendency of Fenhongzhong.