The effects of physiological age of seed potatoes on the growth and development of the subsequent crop

Four field trials were conducted to determine whether physiological age (p-age) of seed tubers affects the subsequent growth of Kennebec and Russet Burbank. Seed potatoes were physiologically aged by allowing them to sprout prior to planting. The degree of aging was quantified as the number of day degrees above a baseline of 4°C, from the time of dormancy break until the time of planting. In the first experiment five p-ages of 0, 250, 500, 750 and 1200 day degrees above 4°C, were imposed on both cut and round seed tubers of Kennebec. The affects of p-age were studied in terms of the growth of the resulting crop. By increasing p-age of seed at the time of planting, emergence was more rapid, a leaf canopy was more quickly established, tuber initiation occurred earlier, and early tuber yields were greater. Physiological age also affected the number of stems per plant so that the maximum number occurred on plants of 250-500 day degxleis >4°C. Although final yields were not significantly different, significant differences occurred with number of tubers and mean tuber weight. With increasing p-age there was a significant increase in mean tuber weight and a simultaneous decline in the number of tubers per plant. There were no significant differences between cut and round seed in their response to p-age. In Experiment 2 the effect of p-age on Russet Burbank was investigated and compared to the effects observed on Kennebec in Experiment 1. Again, p-older seed emerged sooner and established a leaf canopy earlier. Increased p-age encouraged early stolon growth and tuber initiation. These effects were comparable to the response of Kennebec. However further effects of p-age on Russet Burbank were relatively small in comparison to the p-age response of Kennebec. Where Kennebec produced most numbers of stems from seed of P-250 - P-500, Russet Burbank produced the least from these treatments. Yield was not significantly affected by p-age but was found to be proportional to the total light receipts intercepted by each treatment. Mean tuber weight increased with p-age but not to the extent which was recorded for Kennebec. Maximum numbers of tubers per hectare occurred for P-500 - P-750 plants which was converse to Kennebec which had the greatest numbers of tubers from P-younger plants. The effect of plant density on the physiological age response was examined by planting seed of P-0, P-500 and P-1200, at 3, 6 and 15 plants per square metre. Certain characteristics of the p-age response described in Exp. 1 were observed across all planting densities. They included increased rate of emergence, and reduced time till crop senescence with increasing p-age. Maximum numbers of stems per plant were achieved at P-500, and yields were reduced when physiological age was P-1200. When plant density was increased, increasing p-age reduced the numbers of tubers which developed on each stem and hence affected the mean tuber weight. The effect of seed type on the physiological age response of Kennebec was examined by p-aging seed to P-0, P-500 and P-1200 and cutting it into splitters, commercially cut and heel-end sets just prior to planting. The p-age response observed for Kennebec in Exp. 1 was again seen in this trial for splitters and to a lesser degree, heel-end sets. Differences in their response were explained by the poor emergence and reduced stem production of the heel-end sets. Commercially cut seed was coMpiised of a high proportion of heel-end sets and sets from the apical portion of the mother tuber. Their response to p-age was midway between that of heel-end sets and splitters.