Effects of Irrigation on Fruit Sunburn Injury Occurrence in Eggplant ‘Senryo’ during Forcing Culture

Abstract

This study assessed effects of irrigation on the occurrence of fruit sunburn injury of eggplant ‘Senryo’. In fields of growers, the rate of fruit sunburn injury occurrence was higher in fields with a low mass water content. In a research field, a treatment was prepared with pF 2.0 or pF 1.6 at the beginning of irrigation during March–June, when injury occurs most often. The difference in the occurrence rate between the two plots was small. Furthermore, when the beginning points of irrigation were set to pF 2.3 and pF 1.6, results showed a higher xylem exudation rate in the pF 1.6 plot. The occurrence rate was significantly lower in the pF 1.6 plot (35%) than in the pF 2.3 plot (43%). However, in the greenhouse with a low soil humus content (20.0 g・kg^–1), the occurrence of sunburn injury was significantly higher than in greenhouse B, where the soil humus content was 30.5 g・kg^–1. Therefore, organic matter was applied continuously for three years in greenhouse A. The results showed that the soil humus content was increased to 26.0 g・kg^–1. The rate of sunburn injury occurrence in greenhouse A was lower than that in greenhouse B, where organic matter had not been applied for three years. The results presented above suggest that the beginning point of irrigation that can reduce sunburn injury occurrence is pF 1.6–2.0. Before planting, the humus content should be raised or maintained by applying of organic matter to improve physical properties of soil.