Effects of harvest injuries on storage rot of potato tubers infected with Phytophthora infestans

We explored the effects of harvest damage on potatoes infected with Phytophthora infestans in 2015 and 2016. Injured tubers were inoculated with zoosporangia suspensions and incubated at 18°C in the dark for 4 weeks. In 2015 and 2016, 38.5% and 74.4%, respectively, of injured tubers inoculated with P. infestans rotted and hyphal masses were apparent on the tuber surfaces. Tubers in the uninjured group rarely rotted even when there were numerous P. infestans zoosporangia on the inoculated tuber surface. The percentage of rotten tubers in the injured/no inoculation group caused by other types of fungi or bacteria increased rapidly, to approximately 20% within one week; however, there was very little increase during the subsequent incubation. Conversely, the percentage of rotten tubers increased with incubation time in the injured/inoculation group and this phenomenon was significant in 2015. These results imply that not only the presence of P. infestans but also surface harvest injuries affect potato storage rot. Storage rot can be minimized by reducing surface injuries and/or decreasing blighted plant material and the population density of P. infestans in the soil at the time of harvest during commercial potato production.