Investigation and analysis of relationship between mineral elements alteration and cork spot physiological disorder of Chinese pear ‘Chili’ (Pyrus bretschneideri Rehd.)

Abstract

Cork spot is one of the most damaging physiological disorders in pear. However, the mechanism of cork spot is unclear. Ca2+ deficiency is considered as the major agent to cork spot. In this study, we investigated cork spot characteristics in Chinese ‘Chili’ (Pyrus bretschneideri Rehd.) and analyzed the relationship between mineral elements alteration and cork spot occurrence. We found early initiation of cork spot disorder in ‘Chili’ at 80 days after full bloom (DAFB). Cork spot in disordered fruit mostly distributed around the fruit eye with necrotic and brown tissues at the spotted site in flesh. At harvest time, cork spot disordered fruit had a smaller size, higher firmness, lower titratable acidity, higher lignin and cellulose content than healthy fruit, while starch concentration was the same between disordered and healthy fruit. Differences of mineral elements content were also found in both leaves and fruits, and Ca2+ distribution was visualized to be concentrated inside cell wall in disordered fruit cells. Principal components analysis (PCA) of mineral elements data showed that fruit samples could be separated according to their healthy or disordered condition at 80 and 160 DAFB. However, no significant correlation was found between cork spot disorder and mineral elements data. Ca2+ concentration was not suggested as the cork spot biochemical marker in our study. At last, we hypothesized the relationship between cork spot occurrence and Ca2+ distribution in ‘Chili’ and summarized the factors probably contributing to Ca2+ deficiency disorder, which would be useful in designing orchard strategies against cork spot.