Disease Note.

Suppression of Bacterial Stem Rot (Erwinia carotovora subsp, caroto-yora) by a High Potassium-to-Nitrogen Ratio in the Nutrient Solution of Hydroponically Grown Tomato. B. N. Dhanvantari, Research Centre, Agriculture and Agri-Food Canada, Harrow, Ontario NOR 1G0. A. P. Papasdopoulos, Research Centre, Agriculture and Agri-Food Canada, Harrow, Ontario NOR 1G0. Plant Dis 79:83. Accepted for publication 10 November 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0083A.

In nutrition experiments conducted on spring greenhouse crops of tomato (cv. CR-6) under nutrient film technique (NFT) and rockwool slab culture in separate years, the effect of varying nitrogen (N) and potassium (K) levels on bacterial stem rot caused by Erwinia carotovora subsp. carotovora (Jones) Bergey et al was tested by adjusting the nutrient solution with low, medium, and high K/N ratios supplied as 300:300, 400:200, and 480:120 ppm, respectively, while constant levels of P, Mg, micronutrients, electrical conductivity, pH (6.5), and a Ca level of 127-183 ppm were maintained. The E. c. carotovora strains TSR0I and TSR05 (1) were used to inoculate the plants in the NFT experiment and only TSR01 in the rockwool slab experiment. In both experiments with the TSR01 strain, stem rot spread with a mean length of 435 mm and 507 mm by 11 wk in plants under low and medium K/N ratios, respectively, whereas it was limited to a significantly (P = 0.01) shorter mean length of 63 mm under the high K/N ratio. Stem rot was also significantly less under the high K/N ratio than under the other ratios in the NFT experiment with the inoculum TSR05. A nutritional regime with a 4:1 K/N ratio, as reported here, may be helpful in suppressing bacterial stem rot in hydroponic tomato.