Comparison of methods for measuring dormancy of potatoes

Comparisons were made of different methods of measuring length of the dormant period of Russet Burbank potato tubers as affected by time of planting and harvest. The study resulted in the following conclusions: 1) when measured from planting or tuber initiation to sprouting, the dormant period of tubers harvested on the same date was longer from an early planted crop than from a late planted crop. 2) When measured from harvest to sprouting, the dormant period was shorter for tubers from an early compared to a late planting. 3) With the same planting date and different harvest dates, when measured from planting or tuber initiation to sprouting, the dormant period was shorter for tubers from an early compared to a late harvest. 4) On the other hand, with the same planting date, when measured from time of harvest to sprouting, the dormant period was longer for tubers from an early compared to a late harvest. Planting date to sprouting was considered the best practical field measure of dormancy since it closely correlated with tuber initiation to sprouting, a method which was more accurate but difficult to determine. Both methods were much better than harvest date to sprouting which is commonly used. In addition, larger tubers from earlier planting had shorter dormancy than smaller tubers regardless of method of measurement due to a probable earlier set. From later plantings, tuber size had no relationship to length of dormancy. Moisture stress significantly reduced dormancy of Lemhi, Russet Burbank, and Nooksack but the Butte cultivar was only slightly affected.