Biological control of bacterial wilt of potatoes caused by Pseudomonas solanacearum.
Seed potato tubers were treated with a selected antagonistic bacterial isolate and coated with CaCO3. An amendment was also prepared, containing the same bacterial isolate. The bacterium, designated as isolate BC8, caused strong inhibition of P. solanacearum in both in vitro assays and growth chamber conditions. In order to test the antagonistic capacity of isolate BC8 under field conditions, a completely randomized design was established in a soil naturally infested with P. solanacearum that included 12 treatments repeated 10 times, each one with 5 replications. The field experiment was planted on Nov. 26, 1986 and the rate of wilt symptoms for each treatment was recorded periodically. Three tubers from each plant in each treatment were assayed for either presence of P. solanacearum or the antagonistic isolate BC8. Treatments that included isolate BC8 had the lowest number of wilted plants and fewest tubers latently infected as well. Using this system, c. 80% of the tubers assayed from plants growing in the naturally infested soil were colonized by the antagonistic isolate BC8 and free of P. solanacearum. It was established that the pathogen was still present in the soil after 2 years of non-potato cropping and that latent infections play an important role in the dispersal of P. solanacearum. The system of delivering bacteria in an amendment proved to be much more efficient in the biological control of P. solanacearum than just coating the seed potato tubers with the antagonistic isolate BC8.