Induction of resistance in common bean by Rhizobium leguminosarum bv. phaseoli and decrease of common bacterial blight

Rhizobium leguminosarum bv. phaseoli was evaluated for its capacity to trigger resistance to common bacterial blight (CBB) of common bean caused by Xanthomonas axonopodis pv. phaseoli (Xap), under greenhouse and field conditions. A common bean cultivar and three lines including two tolerant lines (Ks51103 and BF13607) and the susceptible cultivar Khomein and line Ks21479, were used. R. leguminosarum bv. phaseoli, was applied as a seed treatment and its effect on disease severity (DS) was compared with untreated (control) plants and with urea fertilizer treated plants in both the greenhouse and the field. R. leguminosarum bv. phaseoli in common bean roots tended to reduce CBB severity and to improve plant growth, particularly the 100-seed weight, in the field. The greatest decrease in CBB in the greenhouse occurred 15 days after inoculation (DAI) of Xap in the cultivar Khomein and line Ks21479, and 30 DAI in lines Ks51103 and BF13607. In the field, however, the greatest decrease occurred 35 DAI in the cultivar and all lines. Furthermore, in the field the greatest improvement in 100-seed weight occurred in the cultivar Khomein treated with R. leguminosarum bv. phaseoli. The potential of using R. leguminosarum bv. phaseoli in the management of CBB and the possible mechanisms that induce resistance in this symbiotic system are discussed.