Rizobactérias promotoras de crescimento vegetal associadas à Mimosa tenuiflora (Willd.) Poir. em área suscetíve l à desertificação de Irauçuba, Ceará

Abstract

Caatinga is a mosaic of seasonally dry forests that covers much of the Northeast region of Brazil (about 70%) and a part of the state of Minas Gerais. The climate in this region is semi arid, with annual rainfall l ess than 800 mm. Despite housing a highly rich biodiversity, this scenario has been changing due to the misuse of its natural resources. The consequences of these actions are the aggravation of the desertification process, which culminates in the loss of p hysical, chemical, biological and economic characteristics of the soil. In the Northeast this process is aggravated by the intrinsic characteristics of the region, making most of the Desertification Susceptible Areas (DSA) in this area. The entire territor y of Ceará is located in an DSA , and three serious desertification nuclei have already been defined in the state: Irauçuba, in the Center N orth; Inhamuns e Médio Jaguaribe Being the core of Irauçuba considered one of the most serious in the country. Studi es have been developed to mitigate these effects, but little is known about microbial diversity and its importance in these locations. Thus, the present study aimed to isolate microorganisms present in the rhizosphere of Jurema preta Mimosa tenuiflora ) sp ecimens, and to evaluate their potential for the promotion of plant growth, aiming at future use as bioinoculants. The samples were collected at Fazenda Aroeira, in the municipality of Irauçuba CE. The plants were removed from a natural area and another ar ea surrounded for 18 years, which are in the process of natural regeneration. Isolation of bacterial strains led to the creation of two collections containing 15 bacteria each . The selected morphotypes were evaluated for phosphate solubilization potential, siderophores production and nitrogen fixation. Some microorganisms were also selected for molecular identification through 16S ribosomal gene analysis. The analyzes showed that the largest number of isolates capable of solubilizing phosphate were present in the rhizosphere of the recovering area, yielding 7 solubilizing strains, compared to only 2 of the natural area. Regarding the production of siderophores, 3 producing strains were obtained from the isolates of the natural area, and 7 from the natural re covery area. Of the 15 isolates from the recovering area, 12 were able to fix nitrogen, while from the natural area 7 positive isolates were detected among the 15 strains tested. The most promising isolate for plant growth promotion was identified as Klebs iella sp. Further studies are needed to verify the potential of this isolate as a bionoculant, as well as the creation of strategies that allow its dissemination in the field.