Effects of Earliness on Heat Stress Tolerance in Fifty Potato Cultivars

Heat stress can seriously reduce the tuber yield of potato (Solanum tuberosum). Early maturing cultivars are usually less affected by heat than late cultivars, which is explained by the avoidance of long exposure to summer temperatures due to the short growing time of early maturing cultivars. To determine whether there are other mechanisms involved in heat tolerance of early cultivars, we conducted correlation analysis between field earliness and growth performance of 50 potato cultivars under both heat-stressed (HS, day/night 35 °C/28 °C) and control conditions (CK, day/night 22 °C/18 °C). We classified the 50 cultivars into 8 scales of earliness and grouped them into early, intermediate and late groups based on the information on field plant maturity in Canada. We found that cultivars known to be early in the field grew similar to late cultivars under heat stress in the greenhouse in terms of traits evaluated, such as chlorophyll content and plant height. Compared with late cultivars, the early cultivars did not show any sign of early maturity under heat stress conditions. The HS/CK ratios of chlorophyll content, plant height, and largest tuber weight (tuber size) were all significantly greater in early cultivars than in late cultivars. Tuber size and field earliness were negatively correlated in CK but positively correlated under heat stress. Clearly, in addition to avoidance, other mechanisms (such as pleiotropic effects of earliness genes) were involved in the better performance of early cultivars under heat stress. These results indicated that the cultivars reprogramed their plant maturity and development under heat stress.