Studies On The Mechanism Of Mango (Mangifera Indica L.) Embryo Abortion In Off-season Cultivation

Mango （Mangifera indica L.） has been considered a famous tropical fruit in the world.Sanya city of Hainan province and its surrounding areas are located in the typical tropical areawhere mango fruit are usually harvested from April to May every year, but may also beharvested in advance from February to March by application of off-season productiontechnology, which contribute to a high economic benefit. However, the production of highratio of embryo aborted fruit seriously decreased the commodity rate of mango fruit, and ithas become the one of the main problems during the off-season mango cultivation. In thisstudy, the main cultivars ‘Jinhuang’ mango was used as experimental materials to investigatethe effect of the flowering on the physiological ecology in mango, to study on the change ofthe floral organ in off-season production, to study embryo abortion of the difference on themidway with normal embryos from cytology, hormone, polyamines and molecular levels, toexplore the reasons of embryo abortion, and to take measures to improve the ratio of theseed-fruit. The main results are presented as follows:1. The flowering efficacy was evaluated after spraying different concentrations of ethephon,potassium nitrate and its mixure with cytokinin. The results showed that the highconcentrations of ethephon reduced the chlorophyll contentes and the net photosynthetic rate.All treatments enhanced the content of the leaves zeatin and ratio of ZR/ABA, resulting in afaster flowering, which is associated with the increased C/N ratio in the leaves first. On theother hand, the effect of high concentrations of ethephon and potassium nitrate treatment isobviously earlier than that in low concentration induce, the various treatments reduce the ratioof hermaphrodite flower and the ratio of embryo normal fruit （big fruit containing seeds）.2. On the off-seasonal mango production, the stamens of ‘Jinhuang’ cultivar was shownas the degeneration, the significant difference has been observed in development of anther inwhich the bigger anther possessed the more pollen quantity with higher maturity, and only afew sac pollen showed the degeneration, the pollen be in live was still account for76.9%. Inthe female gametophyte, ovule appeared malformation, shrinking deformation and ovaryshowed growth sometimes in flat, there was similarity phenomenon around the conductingtissue cells in the embryo sac nuclear during fracture. When the megaspore developed in stage of eight nucleolus, there was a phenomena that the synergids, polar nuclei or antipodals insame or different ovules degenerated, all those factor might affect the fertilization of theovule.3. Djacent was polygonal, its vacuole was small and cell wall was twist with theosmiophilic deposits accumulated. The central cell bigger than normal, the proplastids wasfew，nutrients loss of activity, which affected the development of embryos and procambiumformed, the endosperm cells cannot be sustained division and development were the reason ofthe embryo stoped developing and induced abortion.4. The relationship between the endogenous hormones level and embryo abortion ‘Jinhuang’ mango fruit at early development stage was investigated. The results showed that thefruit embryo abortion was finished within30d, indicating20～30d could be critical periodfor embryo development. The difference in size between embryo normal and abortion fruitmainly depended on the fruit flesh; the IAA, ABA contents in embryo aborted were higherthan those in the seed at the initial stage, but the lower contents of GA₃and ZT were observed,compared to those in the normal embryo. In contrast to seed fruit, the lower GA₃contentswhile higher ZT, IAA and ABA levels were existed in embryo abortion fruit pulp. Moreover,the higher contents of GA₃and ZT and lower ABA level were favorable to normal embryodevelopment. The decreased ZT, enhanced ABA contents as well as lower（GA₃+IAA+ZT）/ABA ratio in embryo comparing with those in pulp were important factors leading to embryoabortion. During fruit development, with the embryo aborted, the lower ratio of（GA₃+IAA+ZT）/ABA in embryo and pulp were the important reasons resulting in small size in seedlessfruit.5. The relationship between the polyamines and embryo was studied by analyzing the freepolyamine content in mango fruit. The result showed putrescine was the predominantpolyamine in the three fractions, Put, Spd, Spm and （Spd+Spm）/Put were lower in embryoaborted fruit than those in normal embryo, and Spd showed significant difference betweenthem. Put and Spd contents increased to higher values in pulp than those in aborted one,the ratios of （Spd+Spm）/Put and Spm/PAs were lower than those in seedless fruit,all of thefactors involved in the embryo abortion.Put contents in pulp was maintained at higher levelfor a relatively long time, Spm contents and Spm/PAs raised sharply after40days fruit set andmaintained constant increase in embryo normal fruit, which could play an important roles inthe development period of the embryo normal fruit exceed than seedless fruit in size.6. Using subtractive suppression hybridization to investigate the difference in genesexpression involved in the process of embryo abortion. Two cDNA libraries from normal seedand aborted seed embryos of ‘Jinhuang’ mango were established to obtain one thousand five hundred and seventy-two high-quality expressed sequence tags （ESTs）, among which1092were obtained from the normal seed tester library and480from the aborted seed tester library.In normal seed tester library, ESTs were comprised of783unigenes, including147contigsand636singletons in contigs; there were297singletons in gene ontology （GO） indicatedcoverage of a broad range of GO categories in the borted seed tester library. Seven candidategenes from different categories were selected for semi-quantitative PCR analysis. Five ESTs（MaAGA、MaSAS、MaAP2、MaERFand MaMADS） were up-regulated in normal embryotissues compared to aborted embryos among them，and the expression of MaMADS inaborted embryos was significantly down-regulated.7. Spraying with low concentrations of spermine, Calcium chloride and urea alternation10days after bloom significantly improved the ratio of seeded fruit. Low concentrations ofspermine and urea had a significant effect on improving the seeded fruit ratio in ‘Jinhuang’variety.