Isolamento de Rizóbios nativos associados ao feijão comum (Phaseolus vulgaris L.) em condições de restrição hídrica

Abstract

In Leguminous, the symbiotic association with nitrogen -fixing bacteria in the roots supplies nitrogen. The efficiency of this association depends of several biotic and abiotic factors. Abiotic factors as temperature and low availability of water can reduce the efficiencyof biological nitrogen fixation. In Brazil, some regions, present long periods of drought and, the productivity of bean require irrigation and application of nitrogen fertilizers. The objective of this work was to isolate and characterize native symbiotic nitrogen - fixing bacteria associated to common bean under conditions of water restriction for the selection of strains adapted at drought conditions. The isolation was made from an experiment in field with different irrigation levels, where two water restriction conditions were simulated: -47 kPa and -66 kPa. Four cultivars of common bean was tested: BRS Requinte, Branquinho, Madrepérola, and ANFc 9 (Agronorte). Thirty days after germination, were sampled root nodules of all cultivars coming of water restriction levels and conducted at the laboratory for bacteria isolation. After nodules disinfection, the isolation of nitrogen-fixing bacteria was made in YMA media with Congo red, in growth conditions of 30 oC and 48 h of incubation. Seven strains identified as FNE01, FNE02, FNE03, FNE04, FNE05, FNE06 and FNE07 presented the characteristics for colonies of rhizobia group according to their color, texture, shape and Gram coloration. The efficiency in bean nodulation of these isolates was tested in Leonard pots under greenhouse conditions with feijão-caupi (Vigna unguiculata) as host plant. In the validation experiment, was assessment: stem diameter, height, shoot biomass, number of nodules, nodule mass, leaf area, and chlorophyll. Two isolates FNE01 and FNE05 showed higher efficiency in nodule formation, increasing leaf area and chlorophyll content being considered promising for later studies on bean nodulation.