Influence of Proline Foliar Application On the Growth Characteristic and Fruit Quality of 'fuji' Apple Trees

Frost damages often occur in several apple tree growing areas. Apple growers have been used many active ways to protect apple trees against frost damage, such as combustor, air moving fan, and overhead sprinkler. However, there is little information available for chemical protectants in apple trees, except plant growth regulators. This study was carried out to find the effects of four different concentrations of proline applications on the frost resistance and growth characteristics of young and mature ‘Fuji’ apple trees, which were one and eleven-year-old, respectively. The application of 50 mg∙L^-1 proline significantly increased leaf fresh weight and leaf dry weight of young ‘Fuji’ apple trees, compared with those on the control. In addition, foliar spray of 50 mg∙ L^-1 proline significantly promotes flower formation in young ‘Fuji’ apple trees. In the growth characteristics of mature ‘Fuji’ apple trees, the current shoot growth were relatively shorter in the 25 or 100 mg∙L^-1 of proline treatments than those on control tree. However, there were no differences in tree height, truck cross-sectional area, and chlorophyll content in the leaves of both young and mature ‘Fuji’ apple trees. Among the fruit qualities of ‘Fuji’ trees, the fruits treated with 10 or 100 mg∙L^-1 proline increased 18% or 22% of fruit fresh weights, respectively. Fruit color, firmness, and soluble solids concentration were not affected by proline foliar applications in ‘Fuji’ apple trees. Double applications of 50 and 100 mg∙ L^-1 proline improved the formation of fruitlets in terminal and axillary blossom in mature ‘Fuji’ apple trees after two frost damages occurred in the blooming season in 2008.