Calcium and the physiology of sweet cherries: A review

Preharvest Ca sprays and postharvest Ca dips sometimes increase fruit Ca levels; but at other times these are ineffective. Similarly, Ca applications by overhead sprinkling during rain or by spraying or by immersion, sometimes reduce rain cracking; but not always. Reduced fruit cracking is usually accounted for as due to improvements in the mechanical properties of the skin - the fruits structural backbone. Calculation shows that osmotic effects of Ca that reduce fruit water uptake are an unlikely explanation. Preharvest or postharvest applications of Ca may also improve fruit firmness, decrease pedicel shriveling and reduce the incidence of fruit rots. The studies reviewed indicate that (1) little is known about the mechanisms and pathways of Ca uptake into the fruit and (2) Ca applications have the potential to reduce cracking and to help retain postharvest quality; but these looked-for effects are often illusive. The lack of consistent behavior is likely due to erratic movement of the polar Ca ion through the cuticle. Future studies should focus on the mechanisms and pathways of Ca penetration into developing sweet cherry fruit and on its final location at both tissue and cellular levels.