Ideal harvesting point of ‘Limeira-IAC382’ trifoliate orange fruits for seed extraction

Abstract Trifoliate orange is one of the rootstocks most used worldwide mainly because it provides excellent quality fruit production. Harvest at the correct time is among factors that determine the physiological quality of seeds. The aim of this study was to identify physicochemical changes in ‘Limeira-IAC382’ trifoliate orange fruits, searching for the ideal harvest moment to obtain high quality seeds. Fruits were harvested at 180, 210 and 240 days after anthesis, stored in cold chamber and evaluated at 0, 15, 30 and 45 days of storage. The following variables were determined: mass loss, fruit color index, soluble solids, total titratable acidity and fruit juice ratio. Seeds were manually extracted and dried until reaching 30% water content. Seeds were used for the performance of germination, electrical conductivity and greenhouse seedling emergence tests. Seeds from fruits harvested at 240 DAA showed higher germination and greenhouse seedling emergence percentage compared to the other treatments until 30 and 45 days of storage in cold chamber, respectively. Storage for 45 days in cold chamber of fruits harvested at 210 DAA increases seed germination rate and the percentage of seedlings from seeds harvested at 180 DAA. It could be concluded that the harvesting of ‘Limeira-IAC382’ trifoliate orange fruits should be performed when fruits reached yellowish peel and low juice ratio, aiming at obtaining seeds with physiological quality.

摘要 枳（trifoliate orange）是全球应用最为广泛的砧木（rootstock）之一，其核心优势在于可产出优质果实。适时采收是决定种子生理质量的关键因素之一。本研究旨在探明‘Limeira-IAC382’枳果实的理化变化，以筛选获取高品质种子的最佳采收时期。试验分别于开花后天数（days after anthesis，以下简称DAA）180、210和240 d时采收果实，将其置于冷藏库（cold chamber）中储存，并于储存0、15、30和45 d时开展相关测定。测定指标包括：质量损失率、果实色泽指数、可溶性固形物（soluble solids）含量、总可滴定酸度（total titratable acidity）及果汁固酸比。采用人工方式脱取种子并干燥至含水量30%，随后开展发芽试验、电导率（electrical conductivity）试验及温室幼苗出苗试验。结果显示，于240 DAA采收的果实所获得的种子，其发芽率及温室出苗率在冷藏储存30 d和45 d时分别显著高于其余处理组。对210 DAA采收的果实开展45 d冷藏储存，可提升其种子的发芽率；同时，180 DAA采收的果实所获种子的出苗率亦得到显著改善。综上，若要获取生理品质优良的种子，‘Limeira-IAC382’枳的采收应在果实果皮呈淡黄色且果汁固酸比较低时进行。