Streptomycin in relation to potato brown rot control.
Both virulent and avirulent forms of the pathogen (Pseudomonas solanacearum) are sensitive to streptomycin and dihydrostreptomycin. Control trials with streptomycin were made on the early maturing, disease-susceptible cv. King Edward and later maturing disease-tolerant Alpha. Application of the antibiotic at 150 and 400 p.p.m. increased wilt incidence. Root exudates of Alpha were poor in amino acids as compared with those of King Edward; however, approx. equal amounts were exuded after antibiotic application. King Edward showed a higher total microbial population in the rhizosphere than Alpha. Application of streptomycin increased this in non-inoculated plants of both cultivars while inoculated plants of the first showed a sharp decline in microbial densities, only Alpha responding with a considerable increase. The increase in disease incidence after streptomycin application was correlated with increased root exudation at early stages of growth.