The presence of oxalate in the pericarp and fruit pedicel is not linked to a shortage of fruit calcium and increase in cracking incidence in litchi

Abstract

SummaryConcentrations of oxalate and calcium in soluble or structural forms, as calcium oxalate in the pericarp, or as oxalate in the fruit pedicel, and the distribution of calcium in the pericarp and fruit pedicel were studied in litchi (Litchi chinensis Sonn.) using cracking-resistant cv. ‘Huaizhi’ and cracking-susceptible cv. ‘Nuomici’. Oxalate in the pericarp existed mainly in a soluble form and was significantly (P < 0.05) higher in ‘Huaizhi’ than in ‘Nuomici’. The concentration of oxalate was higher than the amount of calcium oxalate. Calcium was first mobilised for the construction of cell walls in the pericarp, despite the high concentration of oxalate in the tissue. ‘Huaizhi’ fruit accumulated more structural calcium and calcium oxalate in the pericarp than ‘Nuomici’ fruit. There was no difference in soluble calcium between the two cultivars. Calcium oxalate was located chiefly in the epidermis of the pericarp, and increased in concentration within 50 d after anthesis (DAA) in ‘Nuomici’ and 64 DAA in ‘Huaizhi’, then decreased as structural calcium increased, indicating that calcium sequestered by oxalate could be remobilised.The fruit pedicel had higher concentrations of oxalate than the pericarp. X-ray microanalysis showed abundant calcium in pedicel tissue adjoining the fruit base, and less calcium in tissues at the fruit base and in pedicel tissue 1 cm from the fruit, suggesting that the pedicel serves as a bottleneck to calcium movement. This bottleneck is not likely to be caused by oxalate in the pedicel. Oxalate in the pericarp and in the fruit pedicel is not linked to a shortage of fruit calcium or to an increase in cracking incidence in litchi.