Bitter pit in the apple variety Sturmer in a pot experiment using low levels of major elements

Abstract

The results of a pot experiment showing the influence of low calcium, low magnesium, and complete fertilizer on the pit incidence and mineral content of Sturmer apples are reported. Low calcium treatment resulted in high incidence of pit, low levels of calcium and high levels of potassium, magnesium, phosphorus, and nitrogen in the fruit compared to complete fertilizer and low magnesium treatments. In the ash, though the proportion of calcium was significantly lower, the proportions of potassium, magnesium, and phosphorus did not change. The difference in the characteristics examined between pitted and sound fruit in the three treatments were in the same direction as those between fruit from low calcium and complete fertilizer treatments, and the differences in calcium level were significant. The response to low calcium treatment was a much greater relative molar increase in nitrogen, potassium, magnesium, and phosphorus than the molar decrease in calcium. The evidence supports an hypothesis that the primary cause of pit is low calcium status which under water stress in the leaves and fruit induces an increase in nitrogen, respiration rate, and mineral content but gives no indication which of these causes the lesions.