Introduction performance of Vietnamese large-fruited Manilkara zapota and its suitable harvesting period in Nanning, Guangxi

【Objective】Manilkara zapota is a tropical fruit with high economic value and development potential. In order to enrich the fruit germplasm resources in the southern region of Guangxi, this study conducted observations and evaluation on the growth status of the M. zapota introduced from Vietnam and the fruit quality at different harvesting periods. The aim of this work was to clarify the adaptability and suitable harvesting period of the Vietnamese large-fruited M. zapota in Nanning, Guangxi, and provide a useful basis for its introduction and cultivation in the southern region of Guangxi.【Methods】 Plants of Vietnamese large-fruited M. zapota introduced from Vietnam were used as experimental materials. The introduction and cultivation experiment were carried out in the Fruit Germplasm Resources Nursery of the Guangxi Subtropical Crops Research Institute. The botanical characteristics, flowering and fruiting habits, fruit growth pattern and yield of the Vietnamese large- fruited M. zapota were observed. The botanical characteristic indicators included plant height, stem circumference, crown width, leaf length, leaf width, petiole length, flower length, flower width, seed length, seed width and seed thickness. The observation of flowering and fruiting habits included the budding stage, initial flowering stage, full- bloom stage, flower withering stage and fruit ripening stage. The observation of the fruit growth pattern was carried out by measuring the transverse diameter and longitudinal diameter of the fruits once every 30 days. In order to determine the appropriate harvesting period of the Vietnamese large-fruited M. zapota, samples were collected 290 days, 310 days, 330 days and 350 days after flowering, respectively. The samples were placed at room temperature for 5 to 7 days for ripening, and then their quality indicators were determined. The quality indicators included the single fruit mass, soluble solids, soluble sugar content, total phenol content, vitamin C content and titratable acid content. The total soluble solids were determined with an ATAGO hand-held saccharometer. The soluble sugars were determined by thermal titration with Fehling reagent. Vitamin C were determined by the 2,6-dichloroindophenol titration method. The titratable acids were determined by acid-base titration. The total phenols were determined with Folin-Ciocalteu reagent.【Results】The Vietnamese large-fruited M. zapota exhibited normal growth, blooming and fruit- bearing in Nanning. The average plant height of 7 years- old trees was 301.40 cm, the crown width from east to west was 293.00 cm, the crown width from north to south was 307.20 cm, and the stem circumference was 26.60 cm. The fruits were oval-shaped, with an average single fruit mass of 96.83 g. The fruit peel was rough, tan in color, and was attached with scurf that could be easily shed. The pulp was yellowish-white, rich and sweet in taste, soft and delicate, with few stone cells, and each fruit had 1 to 3 seeds. The tees bloomed twice a year, with the first flowers blooming from early April to the end of June, and the second batch from early August to the end of October. The trees began to bear fruit in the third year after transplantation. The average yield per plant in the first year of fruiting was 3 kg, and the average yield per plant in the seventh year was 26.71 kg. The trees could still grow normally in an environment with a minimum temperature of 6 ℃. The first batch fruit growth curve was“S”shape, that is, the growth was slow in the initial stage, there were two rapid growth stages in the middle stage, and the growth slowed down until maturity in the final stage, and the growth and development period of the fruit was about 330 days. The mass of single fruit, the content of soluble solids, and the content of soluble sugar showed a trend of first increasing and then decreasing during ripening. The content of vitamin C and the content of titratable acid decreased continuously. The content of total phenols fluctuated in the early stage, then gradually increased towards the mature stage, and subsequently decreased again. The first batch fruits harvested 330 days after flowering had the highest single fruit mass (105.94 g), soluble solids content (20.8%), soluble sugar content (247.72 mg · g- 1 ) and total phenols content (4.34 mg·g-1 ), a relatively high vitamin C content (149.04 μg·g-1 ), a low content of titratable acid (0.96%).【Conclusion】The Vietnamese large-fruited M. zapota could adapt to the environmental conditions in Nanning, Guangxi, and complete the normal growth and development cycle. During the period of introduction and trial planting, it demonstrated the characteristics of strong growth vigor, early production, and excellent fruit quality, and showed good prospects for popularization in the southern region of Guangxi. In addition, the suitable harvesting period of the Vietnamese large-fruited M. zapota in Nanning would be 330 days after flowering.