The Use of a Gamma-irradiated Mutants of F. solani f.sp. phaseoli with Reduced Pathogenicity for the Biological Control of Fusarium Root Rot of Bean (Phaseolus vulgaris) in Field Conditions

Fusarium solani was isolated from diseased roots of common bean (Phaseolus vulgaris) grown in fields which were severely infected with Fusarium root rot of bean in Markazi Province of Iran. Specific PCR primer pairs were used for the identification and verification of F. solani (Mart.) f.sp. phaseoli (Burkholder) W.C. Snyder and N.H. Hans. Spore suspensions of F. solani f.sp. phaseoli were subjected to gamma irradiation at 130 Gy using Cobalt-60, and 700 mutants were generated. All 700 mutagenized colonies were tested in the greenhouse for reduced pathogenicity. One mutant (M23) showed the best expected reduction of Fusarium root rot and was chosen to be tested as a biocontrol agent in field experiments. Different concentrations of avirulent mutant (avr-M23) were used against Fusarium root rot in the infested field and their effects on the yield of bean plants were evaluated. The biocontrol effect of avr-M23 on Fusarium root rot was significantly improved with increasing its concentration from 103 to 109 conidia ml-1. Best yields (no. of pods per plant and 100-seed weight) were obtained at concentrations of 106 and 109 conidia ml-1. This study confirms that avr-M23 can be used as a biocontrol agent to protect bean plants from Fusarium root rot under field conditions.