Resumo

The Embrapa Agrobiologia has developed an inoculant for sugarcane composed of a mixture of five endophytic diazotrophic bacteria aiming to reduce the use of nitrogen fertilizers applied to crop. These strains have also the potential to act as biocontrol agents. Here, we carried out in vitro assays to determine the ability of the inoculant strains to inhibit growth of fungi species that attack sugarcane plants. The five diazotrophic bacterial strains: Gluconacetobacter diazotrophicus BR11281, Burkholderia tropica BR11366 , Azospirillum amazonense BR11115 , Herbaspirillum seropedicae BR11335 and Herbaspirillum rubrisubalbicans BR11504 were tested in a randomized block design against four fungi isolates (Colletotrichum falcatum 12/05, Fusarium moniliforme 63/08, Ceratocystis multianulata 2H and Thielaviopsis sp. 30/74) comparing with a control (no bacteria) in three replicates. Bacteria were cultivated in test tubes containing 5 ml of Dygs liquid medium for 48h at 200 rpm and 30°C. The fungi were previously cultivated in Petri dishes containing PDA medium for 10 days at 20°C and photoperiod of 12 h. The bioassay consisted in streaking two lines of each bacterial strain equidistant and parallel within the Petri dishes containing the PDA medium. Afterward, one mycelia disk of about 1 cm in diameter was inoculated between the bacterial rows. The inhibition of fungal growth was observed seven days after inoculation. The data were submitted to the F test using the SAS system ver.9.0. The results showed that BR11366 strain significantly suppressed growth of all fungi isolates, while the BR11504 strain suppressed the 12/05, 30/74 and 2H isolates. The strains BR11115 and BR11335 only suppressed growth of 2H and 30/74 isolates, respectively, while the BR11281 strain only suppressed the 2H isolate. These results showed a variation in the antifungal activity of the bacterial strains against the fungi probably due to the production of different substances such as chitinase and glucanases enzymes that inhibited growth of the fungal species. The ability of the strains on control fungal pathogens of sugarcane indicate that these strains may play additional role such as biocontrol during the interaction with the sugarcane plants