Indução de resistência à antracnose em Phaseolus lunatus por bactérias fixadoras de nitrogênio

Abstract

Plant defense mechanisms are activated when challenged with the causative agent of the disease. Induced defense processes can be of two types: acquired systemic resistance (SAR) and induced systemic resistance (ISR). SAR is activated by biotic and abiotic factors and ISR is activated by microorganisms present in the rhizosphere. Nitrogen-fixing bacteria are symbionts of the roots that supply nitrogen to legumes. The interaction involves the suppression of the plant's defense system, but there are reports of effects associated with the induction of resistance to some pathogens. Thus, the objective was to evaluate the contribution of symbiosis in the resistance of Phaseolus lunatus to anthracnose. Rhizobia were isolated from nodules obtained from spontaneous infection of 19 ethnovarities of P. lunatus. The isolated bacteria were morphophysiologically characterized. Two rhizobial isolates were selected, one with high nodule potential (CECA R19) and one with low nodule capacity (CECA R01). Bacterial isolates were inoculated into four broad bean ethnovarities with the following characteristics: F1CGG (high nodulation rate and resistant to anthracnose); RTKC (high nodulation rate and susceptible to anthracnose); PCGG (low nodulation rate and resistant to anthracnose); FFG (low nodulation rate and susceptible to anthracnose) and compared with the control treatment and the treatment where mineral nitrogen was supplied (corresponding to 50 kg ha-1 of N). It was found that plants inoculated with isolates CECA R01, CECA R19 and plants fertilized with mineral nitrogen had lower disease severity at 3 and 5 days after inoculation, in addition to having higher shoot biomass and dry matter when compared to the treatment. control. At the end of the evaluation, the plants fertilized with mineral nitrogen and those inoculated with the isolates CECA R01 CECA R19 were classified as moderately resistant and the plants of the control treatment as highly susceptible.

Keywords: biological control; biological nitrogen fixation; anthracnose; innate resistance.