The yield of potato plants as affected by stem canker (Rhizoctonia solani), blackleg (Erwinia carotovora subsp atroseptica) and by neighbouring plants

Potato seed tubers inoculated with Rhizoctonia solani and Erwinia carotovora subsp. atroseptica, to induce stem canker and blackleg respectively, were planted with uninoculated seed tubers in field experiments designed to measure the effects of the diseases and of neighbouring plants on tuber yield. Gaps were also included. The plant variables total and ware (> 150 g) yields and tuber numbers were affected by disease, and also by competition from the two plants on either side in the same row (first neighbours), and increased as competition from neighbouring plants decreased. Plants adjacent to the first neighbours also influenced yields of plants with stem canker but those in adjacent rows did not have a significant effect with either disease. Both diseases altered the tuber size distributions, which were also modified by neighbouring plants. The data were used to predict total and ware yields for crops containing different proportions of healthy, diseased and missing plants.