Maximização da fixação biológica do N2 pela interação BPCPs X Rizóbios X FMA no Caupi

Abstract

The cowpea Vigna unguiculata [L.] Walp. is the main subsistence crop in the semiarid and a low cost source of protein especially for the poor population. The crop production is low in the Northeast due to the non use of agricultural inputs, among them nitrogen. The use of microorganisms to increase agricultural production is probably one of the most important tactics for today in the world. This is due to the emerging demand to decrease dependence on chemical fertilizers and the need for development of sustainable agriculture. Among the biological systems involving plants and microorganisms, there are the legumerhizobia symbioses with the most economical expression, legume-arbuscular mycorrhizal fungi and the use of plant growth promoting bacteria(BPCPs). The objectives of this study were: to determine the viability of co-infection of cowpea seed by the co-inoculation of Paenibacillus, Brevibacillus and/or Bacillus in the symbiosis Bradyrhizobium-cowpea; characterize the strains concerning production of the indole acetic acid (IAA) and phosphate solubilization evaluating the synergism among microorganisms as well as evaluating the response of the triple inoculation (Glomus x Bradyrhizobium x Paenibacillus) in promoting cowpea growth as an alternative to maximize the biological nitrogen fixation (BNF). The first part of experiments was conducted in the laboratory and in the greenhouse of the Agronomic Institute of Pernambuco (IPA) using the cowpea (Vigna unguiculata L. Walp.) cv. "IPA - 206. The strains of Bacillus, Brevibacillus and Paenibacillus used were: Bacillus sp. (ANBE 31, 449, 450, 451 and 461), B. cereus (440), B. subtilis (438, 441, 454, 455 and 459), B. pumilus (444, 445 and 448), B. megaterium (462), Brevibacillus brevis (447),Paenibacillus brasilensis (24, 172 and 177), P. graminis (04.21 MC, MC 22:13 and BR 60106), P. polymyxa (S21) and P. durus (RBN4). The second part of the experiment was conducted in a greenhouse of IPA, using the same legume in the previous experiment. The treatments used were: strains of Bradyrhizobium sp. (BR 3267 and EI – 6) inoculated alone; inoculation in combination with the strains (BR 3267 + EI - 6), controls (absolute (TA) and nitrogen (TN)), combined with the presence and absence of arbuscular mycorrhizal fungi (AMF - Glomus etunicatum ) and plant growth promoting bacteria (BPCP - Paenibacillus brasilensis (24) in a 5x2x2 factorial. Treatments contrasts were performed to study the variables. The microorganisms showed neither capacity to produce IAA nor solubilize phosphate. Synergism was observed between strains of Bacillus, Brevibacillus and Paenibacillus co-inoculated with Bradyrhizobium in cowpea. The inoculation with Paenibacillus brasilensis (24) was higher than the other strains providing a better symbiotic performance. Co-inoculation Bradyrhizobium and Bacillus pumilus (444) inhibited the symbiotic eficiency of cowpea. The inoculation with Bradyrhizobium sp. (BR3267 + EI 6) x Glomus etunicatum favored the nitrogen acquisition and phosphorus availability to cowpea plants. The inoculation with Paenibacillus brasilensis (24), increased the process of infection by Bradyrhizobium sp. and Glomus etunicatum and stimulated the promotion of cowpea growth. It is important to report that the nitrogen from the symbiosis was sufficient to supply the needs of plants.