Rhizospheric streptomycetes as potential biocontrol agents of Fusarium and Armillaria pine rot and as PGPR for Pinus taeda

Abstract

Pinus taeda is one of the main timber trees in Brazil, occupying 1.8 million ha with an annual productivity of 25-30 m 3 ha -1 . Another important species is Araucaria angustifolia, belonging to the fragile Rainforest biome, which for decades has been a major source of timber in Brazil. Some diseases that affect the roots and/or the stem of these trees and cause ''damping-off'' of the seedlings, with economic and environmental losses for the forest sector, are caused by the plant pathogenic fungi Fusarium sp. or Armillaria sp. This research project intended to isolate actinobacteria from the Araucaria rhizosphere, which present an antagonistic effect against these fungi. After the selection of the best pathogen inhibitors, morphologic characteristics, enzyme production, and their effect on the growth of Pinus taeda were studied. The actinobacteria were tested for their antagonistic capacity against Fusarium sp. in Petri plates with PDA as substrate. The inhibition zone was measured after 3, 5, 7, and 10 days. Of all the isolates tested, only two of them maintained inhibition zones up to 4 mm for 10 days. The inhibition of Armillaria sp. was tested in liquid medium and also in Petri dishes through the evaluation of the number of the fungal rhizomorphs in dual culture with the actinobacteria. It was found that all five isolates were able to inhibit the rhizomorph production, with the best performance of the isolate A43, which was capable of inhibiting both fungi, Fusarium and Armillaria. In a greenhouse experiment, the effect of five isolates on the growth of Pinus taeda seedlings was tested. Plant height, stem diameter, root and shoot dry matter were determined. The Streptomyces isolate A43 doubled plant growth. These results may lead to the development of new technologies in the identification of still unknown bacterial metabolites and new management techniques to control forest plant diseases.

Armillaria altimontana Is Associated with Healthy Western White Pine (Pinus monticola): Potential in Situ Biological Control of the Armillaria Root Disease Pathogen, A. solidipes

“…However, trees colonized by both A. altimontana and A. solidipes displayed a reduced growth and survival similar to trees colonized by only A. solidipes (Table 4), which suggests that once A. solidipes has colonized the cambial tissue of living roots, it may have a competitive advantage over A. altimontana as a pathogen on substrates within a living host. Understanding the biotic (e.g., [65][66][67][68][69][70][71][72][73][74][75][76]) and abiotic (e.g., [5]) environmental factors that influence the dynamic interactions of A. altimontana and A. solidipes seems key to the development of management practices for Armillaria root disease in coniferous forests of the interior western North America.…”

Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens

“…Actinomycetes strains like Micromonospora sp., Streptomyces spp., Streptosporangium sp., and Thermobifida sp., are recorded as best to colonize the plant rhizosphere, showing an immense potentiality as biocontrol agent against a range of root pathogenic fungi (Franco-Correa et al, 2010). Rhizosphere streptomycetes as potential biocontrol agent of Fusarium and Armillaria pine rot and as PGPR of Pinus taeda were reported (de Vasconcellos and Cardoso, 2009). Evidences are now available on actinobacteria used in the control of R. solani and Pseudomonas solanacearum in tomato and Colletotrichum musae in banana (Taechowisan et al, 2003).…”

Diversity of Plant Associated Actinobacteria

“…Actinobacteria could play an important role in plant health by acting as plant growth promoting rhizobacteria (Hamdali et al 2008;Hasegawa et al 2008;de Vasconcellos and Cardoso 2009) and as the main microorganisms implicated in controlling the infection of roots by soil-borne pathogenic fungi and bacteria (Williams et al 1989, Hamby 2000, El-Tarabily and Sivasithamparam 2006. Plant growth promoting rhizobacterial (PGPR) effects rely essentially on their ability to solubilize phosphate (El-Tarabily et al 2008) or to produce phytohormones (El-Tarabily 2008; Hamdali et al 2008).…”