‘糯米糍(73-S-20)’荔枝之種子發育與環刻促進著果

Abstract

‘No Mai Tsz (73-S-20)’ is an excellent shrivel-seed litchi cultivar, but with low yield and unstable propotion of shriveled seed. The object of this thesis was to study the seed development, the factors causing the variation of the percentage of shrivel seed, and tried to enhance the fruit set in ‘No Mai Tsz’. Experiments were conducted in 2007 and 2008 to investigate the seed development in ‘No Mai Tsz’ litchi by paraffin- or hand-sectioning. Mature fruits were harvested and classified as normal-, small-, and shriveled-seed fruit based on the development condition of the seeds, and investigated the fruit characters and quality. The percentage of seed without any embryo growth was 90.9% initially but decreased gradually thereafter. However, most of embryos without cotyledon or aborted at the late stage of seed development. At 63 DAB (day after full bloom) the seeds became mature, the percentage of normal seed, seed with smaller cotyledon, seed without cotyledon outline and seed without any embryo were 11.5%, 11.5%, 34.6% and 42.3%, respectively. Those seeds without cotyledon outline became brown in color. It was uncertain that the seeds without any embryo were derived from stenospermocarpy or from parthenocarpy. The shriveled-seed fruits had less fruit weight than the normal-seed ones but their aril weight and total soluble-solid content were not significantly different. The flowers of ‘No Mai Tsz’ litchi were pollinated manually by using the pollens of ‘No Mai Tsz’ or ‘Hak Ip’ varieties. The percentages of shriveled-seed from open pollination were 46.3% and 80% in 2007 amd 2008, respectively, and were significantly higher than 0% and 30.2%, respectively, derived from outcross. The percentages of shriveled-seed from selfcross were 38.4% and 66.7%, respectively, in 2007 and 2008 and were not significant different from those of outcross and open pollination. When the hermaphrodite function as female, hermaphrodite function as male of ‘Hak Ip’ bloomed sequentially in the orchard, the percentage of shriveled-seed derived from simultaneously open flowers in ‘No Mai Tsz’ were 99.6% and 69%, respectively, and 50.9% when flowers of ‘Hak Ip’ were not present. When the flowers of ‘No Mai Tsz’ were emasculated and bagged to prevent from pollination, 9.2% of flowers resulted in parthenocarpic fruits with fruit and aril weight of 4.2 gand 2.9 g, respectively, and without any economic value. These results suggested that pollination is essential for the development of aril and fruit to the economical size in ‘No Mai Tsz’ litchi. The relationship between pollination and the formation of shriveled-seed or seedless fruits are discussed. Outcross may decrease the percentage of shriveled-seed fruits but other unknown factors could not be excluded. Girdling, flower-thinning and 2,4-D were tried in 2007 and 2008 to increase the yield and improve the fruit quality of ‘No Mai Tsz’ litchi. The rate of flushing of the girdled trees was higher than ungirdled ones up to the middle period of fruit growth. Also, the percentage of fruit-cluster formation and the yield of individual trees and the total soluble solid contents on girdled tree were higher than the ungirdled ones during the year with low percentage of shriveled seed. On the other hand, flower thinning and 2,4-D application did not enhance fruit set and fruit quality. These results suggested that girdling just before anthesis is beneficial for enhancing yield in ‘No Mai Tsz’ litchi.