The congeneric strain Ralstonia pickettii QL-A6 of Ralstonia solanacearum as an effective biocontrol agent for bacterial wilt of tomato

The role of Ralstonia pickettii as a congeneric rhizobacterium of plant pathogenic Ralstonia solanacearum has not been investigated in biocontrol of bacterial wilt of tomato. Our preliminary study showed that the population of R. pickettii was significantly higher than that of R. solanacearum in the rhizosphere of healthy tomato plants in a heavily diseased field with bacterial wilt. Due to its good performances in inhibition of R. solanacearum in vitro and colonization of the rhizosphere soil and stem of tomato, R. pickettii QL-A6 was selected for suppression of R. solanacearum by use of the soil drench (SD) and stem injection (SI) methods in greenhouse. By the SI method, disease incidence was reduced by 71.2% on the average with an inoculation dosage of only about 105 cfu of R. pickettii QL-A6 per plant. By the SD method, disease incidence was reduced by 52.9% on the average but needed a higher inoculation dosage of about 109 cfu of R. pickettii QL-A6 per plant. Thus, the SI method was chosen for further testing in field. The field disease incidence in R. pickettii QL-A6 treated plots was 8.8% at harvest time, while that in the sterilized water treated plots was as high as 33.1%. The population ratios of R. pickettii QL-A6 to R. solanacearum in the aboveground parts of field plants injected with R. pickettii QL-A6 ranged from 2 to 163. It is concluded that direct injection of R. pickettii QL-A6 in stem of tomato could be an alternative to chemical pesticides for biocontrol of R. solanacearum.

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► A Ralstonia pickettii strain QL-A6 was isolated from the rhizosphere of tomato.
► QL-A6 is a rhizosphere and vascular tissue colonizer as good as Ralstonia solanacearum.
► QL-A6 preferentially took over the intrusion sites of R. solanacearum.
► Bacterial wilt of tomato was successfully suppressed by QL-A6.