Phytohormones and Antibiotics Produced by Bacillus subtilis and their Effects on Seed Pathogenic Fungi and on Soybean Root Development

Abstract

Bacteria belonging to the genus Bacillus were isolated from soil samples of Parana´State, Brazil, with the aim of evaluating their potential biological control of soybean seed pathogens. Strain PRBS-1 was selected, showing similar effectiveness to that of the strain AP-3, used as a reference due to its known antibiotic potential. The sequencing of the ribosomal 16S rRNA gene confirmed that both strains belong to the species B. subtilis, although showing high genetic diversity in relation to this species. Both strains inhibited five soybean seed pathogenic fungi in vitro, Rhizoctonia solani, Colletotrichum truncatum, Sclerotinia sclerotiorum, Macrophomina phaseolina and Phomopsis sp. Furthermore, the metabolites of AP-3 increased production of root hairs, while the metabolites of PRBS-1 stimulated outgrowth of lateral roots in soybean. The antibiotic effect of both strains seemed to be related to compounds of the iturin group, while the root growth promotion by PRBS-1 was at least partially related to the production of indoleacetic acid. The results have shown the potential of using selected strains of B. subtilis in the biological control of seed pathogens, as well as in promoting soybean growth.

Bioprospecção de rizobactérias promotoras de crescimento em Brachiaria brizantha

“…Inicialmente, para avaliar o antagonismo, foi utilizado o método de pareamento em placas de Petri contendo o meio Batata Dextrose Agar (BDA) segundo metodologia descrita por Araujo et al (2005). Foram utilizados os seguintes fungos fitopatogênicos: Aspergillus niger (Isolado LMU 12) isolado originalmente de sementes de milho e Fusarium oxysporum f. sp.…”

“…A influência das rizobactérias no crescimento das plantas tem sido atribuída a efeitos indiretos associados ao controle biológico de patógenos secundários (Araujo et al, 2005). No entanto, em alguns trabalhos, a promoção de crescimento de plantas, por rizobactérias, também tem sido relacionada à produção de fitohormônios e enzimas líticas (Vassilev et al, 2006).…”

“…Nestas situações rizobactérias que produzem hormônios podem mudar a morfologia radicular e aumentar sua biomassa, ampliando com isso a capacidade de exploração do solo (Malik et al, 1997). Araujo (2008), em estudo de inoculação de Bacillus subtilis em diferentes culturas, demonstrou que a inoculação aumentou significativamente o teor de nitrogênio no tecido foliar de milho, mesmo considerando que a espécie bacteriana introduzida não é diazotrófica, porém já foi caracterizada como produtora de hormônios (Araujo et al, 2005).…”

Physiological potential of rice seeds treated with rhizobacteria or the insecticide thiamethoxam

“…Seed lot 4, with initial germination of 71%, in control treatment, has presented germination percentage of 83% after microbiolization with the strain DFs306 of rhizobacteria ( Table 2). The stimulus to germinations, induced by rhizobacteria strains, may be related to production of hormones, such as gibberellins (Holl et al, 1988) and auxins (Araujo et al, 2005), as well as by enzymes, such as ACC (1-aminocyclopropane-1-carboxylate) deaminase. For Glick et al (1995), this enzyme can stimulate vegetal growth, particularly growth of roots, by kidnapping and hydrolyzing ethylene of the seeds.…”

“…fluorescent, isolated from rhizoplane of rice and green pepper (Capsicum annuum L.) plants. For Araujo et al (2005), rhizobacteria can produce hormones, such as acid indoleacetic (IAA) and indolebutyric acid (IBA), besides the secretion of enzymes that are important for nutrition of plants (Powar and Jagannathan, 1982). In a study on action of hormones in the germination of soybean seeds, Vieira and Castro (2001) have observed that the intermediary concentration of auxin hormone has significantly increased germination.…”