Potato Cultivar Susceptibility to Pythium Leak as Influenced by Harvest and Early Storage Temperatures

Leak is caused primarily by the fungus-like organism Pythium ultimum, which can cause severe crop loss in storage. Previous research has shown temperature as a major contributing factor to the incidence of leak in stored potatoes. The hypothesis that pulp and early storage temperatures affect cultivar susceptibility of leak has not been studied. The objective of this study was to determine the leak susceptibility of multiple russet-skinned potato cultivars and understand how leak susceptibility is affected by pulp and early storage temperatures. To accomplish the objective, Russet Norkotah selections (CO-3, TXNS-112, TXNS-278, TXNS-296, and Standard) were bruised and inoculated with a dilute spray solution of oospores of P. ultimum and stored at 21.1 C for four days to determine susceptibility between selections. To understand how pulp temperature affects cultivar susceptibility, pulp temperatures of Bannock Russet, Clearwater Russet, Russet Burbank, Ranger Russet, Teton Russet, and Umatilla Russet tubers were equilibrated to 12.8, 15.5, 18.3, and 21.1 C bruised, inoculated, and maintained at the same temperatures for four days. To address the effect of pulp and early storage temperature, cultivars Bannock Russet, Russet Norkotah CO-3, Russet Burbank, and Umatilla Russet tubers at tuber pulp temperatures of 15.5 or 21.1 C, were bruised, inoculated, and then held for 4 days at early storage temperatures of 12.8, 15.5, 18.3, and 21.1 C to simulate the ability to alter pulp temperatures with storage conditions. Selections of Russet Norkotah were similar in leak incidence; however Standard Russet Norkotah was significantly more susceptible. The impact of pulp temperature at bruising and inoculation showed all cultivars were significantly less susceptible to leak (19 to 63% incidence) at 12.8 C than at 21.1 C (72 to 93% incidence). When pulp temperatures were 15.5 or 21.1 C at bruising and inoculation and then exposed to early storage temperatures of 12.8, 15.5, 18.3, and 21.1 C, leak incidence was 11, 34, 59, and 74%, respectively; indicating the overriding impact that immediately cooling potatoes, opposed to initial tuber pulp temperatures, has on leak development. Cultivar susceptibility of leak was affected by temperature. Results highlight the importance of growing cultivars that are less susceptible to leak and to harvest susceptible cultivars when pulp temperatures are below 15.5 C or cool tubers below 15.5 C when adequate refrigeration or cooling air are available to rapidly modify temperatures in storage.