Plant growth promoting rhizobacteria as agents in the biocontrol of eucalyptus mini-cutting rot

Abstract

The effectiveness of ten plant growth-promoting rhizobacteria (PGPR) was evaluated for the control of mini-cutting rot of eucalyptus caused by Cylindrocladium candelabrum and Rhizoctonia solani. Inhibition of the "in vitro" mycelial growth of each pathogen differed with PGPR isolate and culture medium evaluated. The most effective group of isolates was FL2 (Pseudomonas sp.), 3918, S1 and S2 (Bacillus subtilis). Under nursery conditions, isolate Ca (Pseudomonas fulva) reduced the incidence of mini-cutting rot caused by C. candelabrum by 33% compared to the control, and by 27% compared to a fungicide treatment (epoxiconazole + pyraclostrobin: 0.4 g.L -1 ). Inoculum density of C. candelabrum in the eucalyptus rooting medium decreased significantly beginning at 10 days after the medium was treated with the PGPR isolates. Isolate Ca was the most efficient in reducing the C. candelabrum inoculum at 15 days and in promoting rooting and growth of eucalyptus. For R. solani, no differences in disease incidence were found among treatments. Sensitivity of the PGPR isolates to ten fungicides differed widely. Tebuconazole completely inhibited 80% of the isolates, but epoxiconazole + pyraclostrobin only inhibited the S1 isolate. Isolate S1 was the most sensitive and isolates 3918 and MF2 the most resistant to the majority of active ingredients tested. Isolate Ca was selected for biological control studies in eucalyptus nursery conditions. Keywords: Eucalyptus, PGPR, Cylindrocladium, Rhizoctonia solani, biological control. RESUMO Rizobactérias promotoras do crescimento de plantas como agentes de biocontrole da podridão de miniestacas de eucaliptoAvaliou-se a eficiência de rizobactérias promotoras do crescimento de plantas (PGPR) no controle biológico de Cylindrocladium candelabrum e Rhizoctonia solani, agentes causais da podridão de miniestacas de eucalipto. A inibição "in vitro" do crescimento micelial dos patógenos variou com o isolado de rizobactéria e meio de cultura. De forma geral, os isolados FL2 (Pseudomonas sp.) e 3918, S1 e S2 (Bacillus subtilis) foram os mais eficientes. Sob condições de viveiro, o isolado Ca (Pseudomonas fulva) reduziu a incidência da podridão de miniestacas, causada por C. candelabrum, em 33% em relação à testemunha e 26,7%, em relação à imersão de miniestacas no fungicida (epoxiconazole + pyraclostrobin: 0,4 g.L -1 i.a.). A densidade de inóculo de C. candelabrum no substrato reduziu a partir de 10 dias para todos os isolados de rizobactérias testados. A partir de 15 dias, o isolado Ca foi o mais eficiente na redução da densidade de C. candelabrum e na indução do enraizamento de miniestacas e no crescimento de mudas de eucalipto. Para R. solani, não houve diferença entre os tratamentos quanto à incidência da doença. Em outro experimento, observou-se ampla variação de resposta dos isolados de rizobactérias aos fungicidas testados. Tebuconazole inibiu completamente o crescimento de 80% dos isolados testados, enquanto epoxiconazole + pyraclostrobin inibiu apenas o crescimento do isolado S1. O ...

Diversity and potential impact of Calonectria species in Eucalyptus plantations in Brazil

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Alleviation of salt stress in germination of Vigna radiata L. by two halotolerant Bacilli sp. isolated from saline habitats of Gujarat

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