Rhizosphere competence of native Rhizobium rhizogenes strain and its use in management of crown gall

Abstract

Native Rhizobium rhizogenes strain UHFBA-212 [141/1A (NCBI: KC488174)]was isolated from rhizosphere soil of peach nursery plant of wild peach collected from Himachal Pradesh. In addition to this,159 isolates were also collected and were screened in vitro for their biocontrol potential against Agrobacterium tumefaciens. Out of these strain, UHFBA-212 showed maximum zone of inhibition i.e. 4.16 and 3.57cm without and after exposure to chloroform against C58.Sequence analysis (16SrDNA) of the strain showed nucleotide homology similar to Rhizobium sp. Amplification of total genomic DNA of the strain with Vir D2 andipt primers didn’t showed amplification with these virulence genes suggesting the absence of tumorigenic factors. In the field conditions, maximum population (329.33x106 cfu/g of soil) was observed in antibiotic resistant mutant of R. rhizogenes strain K84 applied on cherry rootstock Colt followed by 285.33 (x 106 ) cfu/g of soil in UHFBA-212 after 9 months at the time of uprooting of plants when applied alone as root dip. Minimum incidence of crown gall (2.00%) was observed in strain UHFBA- 212 co inoculated with strain C58 as seed treatment on behmi seeds. The data on population indices in rhizosphere and incidence of crown gall further suggested that for better management of disease R. Rhizogenes isolates should be either equal or more in population than that of A. tumefaciens isolates. Strain UHFBA-212 controls crown gall as effectively as strain K84 and can be exploited against tumorigenic isolates under field conditions.