Investigation of effects of different treatments on sunburn in fruit of hicaznar cultivar of pomegranate (Punica granatum L.cv. hicaznar)

This study was carried out to determine effects of kaolin and shading treatments on sunburn in fruits of Hicaznar cultivar of pomegranate (Punica granatum L.cv. Hicaznar) and investigate anatomical differences in peel of fruits with or without sunburn. For this aim, the study was concluded in two of separated part. In the first part of the study, trees in the area selected for shading were first covered with green covering material providing 35% shading on July 30th. Then, effects of kaolin applications of on sunburn in the shaded and non-shaded areas were determined by applying 3% of kaolin at three different periods with four applications each starting at different dates in a weekly intervals. [Period I (KI : July 30, August 6, August 13 and August 20), Period II (KII: August 6, August 13, August 20 and August 27), Period III (KIII: August 13, August 20, August 27 and September 10)]. In the second part of the study, anatomical differences in peel of Hicaznar fruit with or without sunburn were investigated. In addition, temperature, humidity, radiation and amount of light on experimental area were recorded and collected by micro metos ag. climate station and their effects on sunburn were determined. Beside these, effects of different treatments on quality of fruit were also determined. This study was conducted in West Mediterranean Agricultural Research Institute in 2003 and 2004 using Hicaznar the most important pomegranate fruit cultivar produced and exported from this region. Laboratory work was done in the pomology laboratory of West v Mediterranean Agricultural Research Institute and the Anatomy Laboratory Department of Pathology, Faculty of Medicine, at the Akdeniz University. At the end of the first experiment, it was found that applications of caolin were the best method for preventing sunburn in fruits of Hicaznar pomegranate cultivar. Applications of kaolin also increased soluble dry matter content and red color of fruits. Among kaolin applications, KI was the most effective application for reducing sunburn in pomegranate fruit. Shading treatments decrease sunburn on pomegranate fruits comparing to the controls, however, it increased fruit cracking when the humidity was high. Besides these it was determined that shading plus kaolin applications was more effective for decreasing sunburn compared to shading treatment alone. At the end of the second experiment, important anatomic differences were observed in peels of pomegranate fruits with and without sunburn. It was also determined that sunburn was first appeared on the cuticle and it stated to disintegrate due to sunburn. Then the epidermis under the cuticle was affected and destroyed by sunburn. In the advance stage parenchyma and other cells composing of the peel of pomegranate fruit were damaged by sunburn. In addition, images obtained by light microscopy showed that , before a visible color change occurred in the peel of fruits accumulation of phenolic compounds, thickening and lignifications of cell walls of cell especially the one closer to the to epidermis. It was also determined that anatomic changes are started before the occurrence of visible symptoms of sunburn in the fruits. Therefore, it is suggested that applications for preventing sunburn should be arrange according to these findings. KEY WORDS: Pomegranate fruit, sunburn, kaolin, shading, anatomy, yield, quality, fruit peel