Plant Disease Research

Crown gall caused by Agrobacterium tumefaciens is most challenging factor in production of healthy nursery plants in stone fruits. Biological control of crown gall of stone fruits by A. radiobacter strain K84 has been a success all over the world. Due to the unavailability of this antagonistic strain is India, studies were focused on the exploitation of other native A. radiobacter isolates in control of crown gall. native A. radiobacter strain UHFBA-218 isolated from rhizosphere soil of cherry rootstock colt, was found to be antagonistic against A. tumefaciens (isolate C58). Frequency of conjugal transfer of agrocin genes and acquisition of virulence genes (VirD2 and ipt) was also found to be minimum in strain UHFBA-218 compared to standard strain K84. Transconjugants obtained from co-inoculation of A. radiobacter UHFBA-218 + A.tumefaciens isolates (C58, I₁ and I₂) showed partial acquisition of virulence genes. Sugarcane bagasse mixed with UHFBA-218 in 1: 5 ratio showed maximum viable counts i. e. 267.00 × 108 cfu/g, significantly at par with K84 (260.00 × 108cfu/g) mixed in the ratio of 1: 5 after eight months of room temperature storage. The rifampin resistant mutants of antagonistic strain UHFBA-218 and K84 persisted in the rhizosphere soil of peach plants for one year. Maximum viable counts i. e. 150.70 × 10⁶cfu/g were observed in rifampin resistant UHFBA-218 (RD) treatment and it was statistically at par with 148.16 × 10⁶cfu/g in rifampin resistant UHFBA-218 (ST) and 144.75 × 10⁶ (cfu/g) in rifampin resistant K84 (RD) treatment. These results therefore provide a new paradigm to exploit this native A. radiobacter strain UHFBA-218 for commercial use as biocontrol agent.