Starch Metabolism in Apple Cultivars, Poster Board #005

Starch hydrolysis in apple fruit is easily visualized by staining fruit with iodine.   The resulting starch patterns are assigned numbers based on charts that are used to guide harvest decisions. Surprisingly little is known about metabolic processes involved in starch accumulation and hydrolysis, and even less about zonal differences within apple fruit and between cultivars. Our objective is to determine the differences in starch hydrolysis in different cultivars.  The starch concentrations and the activities of key starch hydrolyzing enzymes among these cultivars and within the regions of the apple are being investigated. In this study, ‘Empire’, ‘Gala’, ‘McIntosh’, and ‘Honeycrisp’ fruit were harvested over several weeks, and the starch concentrations compared with the starch pattern index (SPI) in each fruit.  Over the sampling period, the SPI ratings ranged from 1 to 7 for ‘Empire’ and ‘McIntosh’, and 1 to 8 for ‘Honeycrisp’ and ‘Gala’.  The starch concentrations in fruit of each cultivar varied at a given SPI.  At a rating of 1, the starch concentrations averaged 309, 227, 189, and 309 mg/g dry weight in ‘Empire’, ‘Gala’, ‘McIntosh’, and ‘Honeycrisp’, respectively.  However, the variation among cultivars was lower at a rating of 3, where starch concentrations averaged 166, 154, 117, and 146 mg/g dry weight, respectively. In addition, starch concentrations on various tissues zones of ‘Empire’ and ‘Honeycrisp’ apples will be presented.