Use of Pseudomonas protegens to Control Root Rot Disease Caused by Boeremia exigua var. exigua in Industrial Chicory (Cichorium intybus var. sativum Bisch.)

Boeremia exigua var. exigua is a recurrent pathogen causing root rot in industrial chicory. Currently, there is no chemical or varietal control for this disease, and thus management strategies need to be developed. This study determined the biocontrol effect of strains of Pseudomonas protegens bacteria with antimicrobial compounds on the fungus B. exigua var. exigua under in vitro, in vivo and field conditions. In addition, root colonization by these bacteria was estimated by molecular analysis. Eighteen isolates of Pseudomonas spp were evaluated and the strains that showed the greatest in vitro inhibition of fungal mycelial growth (mm), Ca10A and ChB7, were selected. Inoculation with the strain ChB7 showed less severity (necrotic area) under in vivo conditions (root trials) compared to the control inoculated with the pathogen (P≤0.05). The molecular analysis revealed that root colonization of plants grown in pots was equal or greater than 70%. Similar levels were observed in the field trials conducted in Selva Negra and Canteras experimental stations (2015-16 season), with values ranging from 85.7 to 70.5% and from 75.0 to 79.5%, respectively. Regarding yield (ton ha-1), values were higher in the treatments inoculated with strains Ca10A and ChB7 (P≤0.05) in both experimental sites, while a lower incidence and severity of root rot were observed in Selva Negra. These results suggest that the Chilean strains of P. protegens are a promising tool for the control of root diseases in industrial chicory.