Effect of Calcium Sources on the Occurrence of Bitter Pit of Gamhong' /M.9 Apple Cultivar in Korea

The ‘Gamhong’ apple cultivar bred by RDA in Korea has interested customers and farmers with its big size and high soluble solid contents. The cultivar, however, is very sensitive to bitter pit, and many farmers dislike cultivating them. This experiment was carried out to reduce bitter pit in seven-year-old ‘Gamhong’/M.9 cultivars using different calcium sources. Treatments consisted of the control, soil application of limestone (200 kg/10 a), foliar sprays of 0.3% and 0.5% CaCl₂ (applied two and four times), and 2% CaCO₃(applied four times). Foliar spray of calcium was applied at one-week intervals from 45 days after full bloom. Results showed that the leaf calcium content significantly increased when applied four times with 0.3% and 0.5% CaCl₂, when compared to the control. The index of bitter pit (0 to 5) significantly decreased when applied four times with CaCl₂ at 0.3% (0.86) and at 0.5% (0.82) compared to 2.25 of the control. Meanwhile, the soluble solid content of fruit was decreased more four times than two times in 0.5% CaCl₂. Results also showed that there was more significant reduction in the soluble solid content when 0.5% CaCl₂ was used as compared to 0.3%.