The genetic diversity of endophytic bacteria in banana ‘Prata Anã’ roots was characterized. Two hundred and one endophytic bacteria were isolated, 151 of which were classified as Gram-positive and 50 as Gram-negative. No hypersensitivity response was observed in any of the isolates. The rep-PCR technique generated different molecular profiles for each primer set (REP, ERIC and BOX). Fifty readable loci were obtained and all of the fragments were polymorphic. Amplified ribosomal DNA restriction analysis (ARDRA) of the isolates based on cleavage with four restriction enzymes yielded 45 polymorphic bands and no monomorphic bands. PCR amplified the nifH gene in 24 isolates. 16S rDNA sequencing of the 201 bacterial isolates yielded 102 high-quality sequences. Sequence analyses revealed that the isolates were distributed among ten bacterial genera (Agrobacterium, Aneurinibacillus, Bacillus, Enterobacter, Klebsiella, Lysinibacillus, Micrococcus, Paenibacillus, Rhizobium and Sporolactobacillus) and included 15 species. The greatest number of isolates belonged to the genus Bacillus. The bacteria identified in this study may be involved in promoting growth, phosphate solubilization, biological control and nitrogen fixation in bananas.

A total of 40 endophytic bacterial isolates obtained from banana tree roots were characterized for their biotechnological potential for promoting banana tree growth. All isolates had at least one positive feature. Twenty isolates were likely diazotrophs and formed pellicles in nitrogen-free culture medium, and 67% of these isolates belonged to the genus Bacillus sp. The isolates EB-04, EB-169, EB-64, and EB-144 had N fixation abilities as measured by the Kjeldahl method and by an acetylene reduction activity assay. Among the 40 isolates, 37.5% were capable of solubilizing inorganic phosphate and the isolates EB-47 and EB-64 showed the highest solubilization capacity. The isolate EB-53 (Lysinibacillus sp.) had a high solubilization index, whereas 73% of the isolates had low solubilization indices. The synthesis of indole-3-acetic acid (IAA) in the presence of L-tryptophan was detected in 40% of the isolates. The isolate EB-40 (Bacillus sp.) produced the highest amount of IAA (47.88 μg/ml) in medium supplemented with L-tryptophan and was able to synthesize IAA in the absence of L-tryptophan. The isolates EB-126 (Bacillus subtilis) and EB-47 (Bacillus sp.) were able to simultaneously fix nitrogen, solubilize phosphate and produce IAA in vitro. The results of this study demonstrated that the isolates analyzed here had diverse abilities and all have the potential to be used as growth-promoting microbial inoculants for banana trees.

RESUMO O objetivo deste trabalho foi avaliar a sobrevivência de oito cultivares de P. edulis Sims. e a reação do maracujazeiro amarelo enxertado sobre Passiflora foetida L. em área com histórico de fusariose (Fusarium oxysporum f. sp. passiflorae) na região de Mossoró/RN. Foram conduzidos dois ensaios, onde foram plantadas oito cultivares de maracujazeiro (FB 200, FB 300, BRS Gigante Amarelo, BRS Sol do Cerrado, BRS Rubi do Cerrado, IAC 273, IAC 275 e IAC 277) e uma cultivar comercial ‘redondo amarelo’ da Topssed® enxertada sobre P. foetida, em área naturalmente infestada com F. oxysporum f. sp. passiflorae. O delineamento experimental adotado foi em blocos ao acaso, com quatro repetições e três plantas por parcela. No ensaio I foi avaliado a sobrevivência das cultivares e no ensaio II, avaliou-se a incidência da fusariose e a classe de reação, identificando os tratamentos como resistentes, moderadamente susceptíveis e susceptíveis. Todas as cultivares (ensaio I) apresentaram baixos índices de sobrevivência aos 180 dias após o plantio. As cultivares não enxertadas (ensaio II) foram classificadas como susceptíveis, com incidência de fusariose variando de 22,22 a 91,67%. Não houve registro de incidência de fusariose no maracujazeiro enxertado sobre P. foetida (ensaio II) durante o período de avaliação, mostrando-se como um porta-enxerto promissor para solos infestados com Fusarium oxysporum.

The north‐east of Brazil is one of the most important melon‐producing regions in the world. Crop yield is often reduced by the occurrence of a root rot disease, caused by Fusarium species. The present study aimed to characterize a collection of 31 isolates with morphological markers of F. solani obtained from melon plants with symptoms of root rot by phylogenetic analysis of the barcode regions EF‐1α and RPB2, and to verify their pathogenicity to melon plantlets. Phylogenetic analysis showed that 29 isolates grouped with reference material of Fusarium falciforme (FSSC 3 + 4) and two with F. suttonianum (FSSC 20). The pathogenicity test showed that isolates of both species cause root rot in melon plants, with no significant difference of virulence between isolates and species with both methodologies used (infested toothpick and infested rice). Melon plants expressed first symptoms 15 days after inoculation, showing yellowing and wilting, with later tipping and rot. To our knowledge, this is the first report of the occurrence of these species causing root rot in muskmelon in Brazil. Our results support monitoring of causal agents of melon fusarioses and will be useful for breeding programmes in the search for plant material with resistance to Fusarium rot.