Pathogenic variability of Verticillium dahliae isolates from potato fields in Manitoba and screening of bacteria for their biocontrol

Verticillium dahliae causes wilt disease in many crops, including potato (Solarium tuberosum). Very few strategies were developed to date to control this disease and are either harmful to the environment and human health or inefficient in reducing inoculum levels in the soil. Establishing a biocontrol strategy, as part of an integrated management program, would be an eco-friendly alternative to reduce the incidence of this disease in potato. The present study evaluated the proportion of V. dahliae among Verticillium spp. recovered from samples of potato collected in Manitoba fields, on the basis of morphological characteristics and polymerase chain reaction assays. The present study also assessed the pathogenic variability among the collected isolates. Over 90% of the recovered Verticillium isolates were found to be V. dahliae. Artificial inoculation of 'Russet Burbank' potato plants with these isolates showed a high degree of pathogenic variability among them, according to their differential ability to progress upward in the plant and cause wilt and browning of the vascular system. The most pathogenic isolates were selected for further experiments where they were challenged with bacteria from a collection of bacterial isolates with potential biocontrol activity. Three of the 18 bacteria initially screened provided a strong inhibition (>50% compared with the control) of V. dahliae growth in vitro. These bacteria were initially isolated from rhizosphere soils and represent potential biocontrol agents.