Calcium carbonate treatments affect cultivation environment around the fruit surface and mitigate sunburn formation and rind puffing of satsuma mandarin fruits

Fruit trees are more susceptible to global warming than other perennial crops. In this study, we investigated the effect of calcium carbonate suspension (CCS) spraying on peel disorders, including the occurrence of sunburn in early-maturing cultivars ‘Miyagawa-wase’ and ‘Okitsu-wase,’ and rind puffing of late-maturing cultivar ‘Aoshima unshu.’ CCS diluted 25 times with water was sprayed onto satsuma mandarin trees twice, in June and July. Sunburn incidence of CCS treatment in the ‘Miyagawa-wase’ fruit surface during summer was significantly reduced by 30% in comparison with that in the control treatment. The specific gravity of the early maturing cultivar ‘Okitsu-wase’ treated with CCS (0.905) was significantly higher than that of the non-treated fruits (0.874). The specific gravity of the late-maturing cultivars treated with CCS was significantly higher (0.851) than that of the non-treated fruits (0.812). The phosphorous distribution in the albedo of fruits treated with CCS was 65% and 31% higher than that of untreated fruits in September and December, respectively. There were no significant differences in the photosynthetic and transpiration rates of the leaves between the CCS and control treatments. However, the evaporation rate of the wetted leaves in the CCS treatment decreased 2 min after the start of the measurement and remained lower than that of the control treatment for the next 8 min. These results indicate that CCS helps mitigate rind disorders in citrus during cultivation by demonstrating protective effects on guard cells and other tissues and improving the fruit surface environment.