Spongy tissue, as one of internal flesh breakdown in mango fruits, is correlated with calcium (Ca) deficiency, and adversely affects fruit quality and yield worldwide. However, the underlying mechanism causing spongy tissue remains unknown. Here, we explored the effects of Ca deficiency on spongy tissue in a susceptible cultivar, ‘Keitt’, at the physiological and molecular levels. Nutrient analysis showed that flesh with spongy tissue had lower Ca content and higher N/Ca, K/Ca and Mg/Ca rations than healthy fruit flesh. Ca accumulation in the cell wall, especially in chelator-soluble pectin, was elevated due to increased pectin content, lower levels of pectin methylesterification, and increased pectin methylesterase (PME) activity. During spongy tissue development, levels of Ca oxalate (CaOx) and oxalic acid both increased, whereas soluble Ca content decreased in the flesh. Transcriptomic analysis of healthy flesh and flesh with spongy tissue revealed 2054 up-regulated and 996 down-regulated genes. Gene ontology term analysis showed that the up-regulated genes were mainly enriched in functions related to the transmembrane transporter activity, calcium ion binding, and the cell wall. Importantly, up-regulated genes in spongy tissue included five glucuronate 4-epimerase (GAE) genes and two galactosyltransferase (GALT) genes, which involved in pectin synthesis; four PME genes which control pectin demethylesterification; and eight autoinhibited calcium-transporting ATPase (ACA) genes and two vacuole H+/Ca2+ exchanger (CAX) genes which contribute to Ca influx in the vacuole. Our findings illustrate a mechanism by which Ca deficiency leads to spongy tissue, which will contribute to efforts to control this physiological disorder.

Internal flesh breakdown (IFB), a serious physiological disorder of mango fruit, causes significant economic losses in Southwest China. We investigated the extent of IFB in 100 mango orchards and how changes in the mineral nutrients of fruit flesh, leaves and soil affect IFB. We found that 76% of the mango orchards showed IFB symptoms, and the average IFB incidence was 10%. Fruit flesh with IFB showed higher average contents of N, P, K and Mg, lower average Ca content and higher average ratios of N/Ca, K/Ca and Mg/Ca. The leaves from orchards with IFB symptoms exhibited a remarkable increase in the average N and Mg contents. No significant difference was observed in the soil nutrient concentrations between orchards with and without IFB fruit. IFB incidence was significantly positively correlated with the N/Ca, K/Ca and Mg/Ca ratios in the fruit flesh. However, when considering individual orchards with IFB symptoms, fruit flesh that exhibited breakdown symptoms had Ca content higher, lower than or equal to that of the healthy fruit flesh. There was a strong correlation between fruit flesh and leaf in the same mineral elements, but neither of them showed a significant correlation with soil. Considering the mango trees were cultivated on steep slopes, and fertilizer was applied at a fixed position, we hypothesized that long-term fertilization in the partial root zone led to the excess of N, K and Mg in soil, which reduced the total flesh Ca content or resulted in the abnormal cellular distribution of Ca in the flesh, and ultimately triggered IFB development.

以果肉溃败病果率不同的13个凯特果园果实为材料,研究了正常果和病果果肉中氮、钾、镁和钙含量变化,及不同形态钙含量变化.结果表明,与正常果相比,病果中氮、钙和镁含量,及镁/钙均显著增加,而钾含量、氮/钙、钾/钙和(钾+镁)/钙均无显著变化.果肉溃败病果率与病果中氮、钾、镁和钙含量,及氮/钙、钾/钙、镁/钙和(钾+镁)/钙之间均不存在显著相关性.与正常果比较,病果中结构钙含量显著增加,水溶性钙含量显著降低.果肉溃败病果率与病果中结构钙含量显著正相关,与草酸钙含量显著负相关.由此推测,凯特杧果肉发生溃败可能与果肉组织细胞水平钙分配不均有关.

[目的]营养元素的合理供应是实现芒果优质高产的基础,研究芒果果实生长发育期大量元素和中微量元素的需求规律,确定芒果合理施肥时间和用量,为芒果的科学精准施肥提供依据.[方法]在攀枝花市仁和区芒果优势种植区选择盛果期的台农1号(15年生)作为试验材料,研究果实发育成熟过程中整个果实矿质元素N、P、K、Ca、Mg、Cu、Zn、Fe、Mn含量及其积累量的变化规律.[结果]花后7～77 d,N、K、Mg、Cu、Zn、Fe、Mn含量分别降低59.55％、38.72％、39.75％、73.85％、82.49％、77.71％和49.50;花后77～105 d,各元素含量相对稳定或小幅降低.花后7～35 d,果实Ca含量增加56.85％,然后表现出下降趋势.整个果实生长发育期,果实P含量相对稳定.从幼果期至果实采摘期,果实中各营养元素积累量逐步增加.除Mn外,其他元素均以果实快速膨大期(花后35～77 d)吸收量为主,占总吸收量的64.38％～74.94％.在整个果实生长发育期间,N/Ca、K/Ca和Mg/Ca整体上均表现出降低趋势;花后7～77 d K/P比值先增加后下降.[结论]果实快速膨大期是芒果果实养分需求的最大期,也是补肥的关键期.