THE STARCH IODINE TEST FOR DETERMINING STAGE OF MATURATION IN APPLES

Abstract

Starch test guides patterned after a guide already available for McIntosh were prepared and evaluated for determining the first acceptable harvest dates of the apple cultivars Delicious and Northern Spy. The McIntosh, Delicious and Northern Spy starch test guides were useful for determining when these cultivars should be harvested. Temperatures during 20 days before the harvest of McIntosh and 40 days before the harvest of Delicious and Northern Spy influenced the rate of starch hydrolysis and thus the starch index reading. Low temperatures favored the conversion of starch to sugar and high temperatures the reverse. This resulted in low starch index readings at first acceptable harvest in the southern apple growing areas of the province and high readings in the northern areas. Since the average interval from full bloom to first acceptable harvest in Ontario is 118 days for McIntosh, 132 days for Delicious and 133 days for Northern Spy, the ambient temperature beginning 98 days after full bloom for McIntosh, 92 days for Delicious and 93 days for Northern Spy must be considered when using the starch test to determine first acceptable harvest date.