| Litchi (Litchi chinensis Sonn.) is a subtropical evergreen fruit tree originating in southern china, and A4 seedless litchi is a non-nuclear variety with good comprehensive characters of good quality and high economic benefits, which is the main push varieties of Hainan Province. However, the serious problems of physiological fruit drop and cracking have led to a decline in the yield and quality of A4 seedless litchi and restricted the improvement of its yield and economic benefit, which has become the major problems of cultivation. Different control measures has been used to control the flowering and fruiting and prevent the fruit from cracking of A4 seedless litchi in previous studies, but the reports on the mechanism of its physiological fruit drop were less. Therefore, the A4 seedless litchi tree of 10-years old was used as the research object to explore the regularity of physiological fruit drop in this study, and the physiological mechanism were studied from the endogenous hormone, enzyme and mineral nutrition, etc. Based on this study, the physiological fruit drop and fruit cracking of A4 seedless litchi were studied to explore the effective and reasonable control measures which can effectively solve the problem of its physiological fruit drop and fruit cracking and reduce the rate of pre-harvest fruit drop and fruit cracking. Thus, it can provide the theoretical basis for the cultivation and management of A4 seedless litchi. The main results were as follows:1. Pre-harvest fruit drop was the main factor that caused the loss of A4 seedless litchi.During the whole fruit development process of A4 seedless litchi, there were four fruit drop peak which appeared on 9d-12d, 21d-27d, 39d-42d and 51d-60d (before harvest)respectively after flowering, and the rate of pre-harvest fruit drop was up to 69.84, which was significantly higher than the other 3 times. Therefore, it was the important period of control for production and cultivation in the future.2. The fruit of just turned yellow fruit and solitary fruit were the main type of dropped fruit during the period of pre-harvest fruit drop. The period of pre-harvest fruit drop mainly appeared at 51d-60d after flowering, and the amount of solitary fruit was 20% higher than that of paired fruit. The amount of turned yellow fruit (the color of fruit peel just turned yellow) was 3.65 times higher than that of turned red fruit. Besides,the diameter, vertical diameter and single fruit weight of turned yellow fruit were significantly less than that of turned red fruit.3. The IAA, CTK, ABA and ETH in abscission part of fruit stem were related to the pre-harvest fruit drop of A4 seedless litchi. During the period of pre-harvest fruit of A4 seedless litchi, the content of IAA and CTK in the abscission part of normal fruit stem were significantly higher than that in the dropped fruit while the content of ABA and ETH in the abscission part of normal fruit stem were significantly lower than that of dropped fruit.Therefore, it could be seen that the increase of the content of IAA and CTK could inhibit the abscission of fruit, and the increase of the content of ABA and ETH could promote the abscission of fruit.4. The enzymes associated with the abscission layer formed in the abscission part of fruit stem were related to the pre-harvest fruit drop of A4 seedless litchi. During the period of pre-harvest fruit of A4 seedless litchi, the activity of CE, pectinase and POD in the abscission part of normal fruit stem were significantly lower than that of dropped fruit.Therefore, the results indicated that the increase of the activity of CE, pectinase and POD in the abscission part of fruit stem could promote the abscission of fruit.5. The content of mineral nutrient in the abscission part of fruit stem was associated with the pre-harvest fruit drop of A4 seedless litchi. During the period of pre-harvest fruit of A4 seedless litchi, the element content of Ca in the abscission part of dropped fruit stem was significantly higher than that of normal fruit while the element content of N, K, Mg and Mn in the abscission part of normal fruit stem were significantly higher than that of dropped fruit.Therefore, the results showed that the increase of the element content of Ca in the abscission part of fruit stem could promote the abscission of fruit while the increase of the element content of N, K, Mg and Mn in the abscission part of fruit stem could inhibit the abscission of fruit.6. The spraying of 0.5mg / L TDZ aqueous solution after flowering and the second physiological fruit drop of A4 seedless litchi could significantly improve the single fruit weight, reduce the rate of fruit drop and fruit cracking, as well as improve the quality of fruit.The single fruit weight was up to 20.80 g by spraying the aqueous solution of 0.5mg / L TDZ,which was the highest in the single fruit weight and significantly higher than control check.The rate of the pre-harvest fruit drop and fruit cracking of the 0.5 mg/L TDZ treatment were up to 44.43% and 5.17% respectively, which were significantly lower than that of control check.7. Different comprehensive control treatment could all significantly reduce the fruit cracking rate of A4 seedless litchi, and by using of the aqueous solution of 100 mg/L 5 -ALA mixed with 0.5% KCl and covered with black garden ground cloth, the rate of the pre-harvest fruit drop and fruit cracking was 38.15% and 6.55% respectively, which were both significantly lower than that of the control check. By using of the aqueous solution of 100 mg/L 5 - ALA mixed with 0.6% KC1 and covered with black garden ground cloth, the fruit quality could significantly be improved, and the content of titratable acid was 0.17%, which was the lowest in all treatments. Besides, the content of Vc was 43.09 mg/100g, which was the highest and significantly higher than the other treatments. |
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