Control of charcoal root rot in Pinus radiata nurseries with antagonistic bacteria

Abstract

The objective of this study was to determine the potential of antagonistic bacteria to control charcoal root rot of coniferous seedlings caused by Macrophomina phaseolina (Tassi) Goid. in forest nurseries. Bacterial isolates were collected from nurseries located between Region Metropolitana and the VIII Region of Chile. Antagonists were initially evaluated in in vitro assays based on the ability to inhibit mycelial growth of M. phaseolina, and subsequently in two trials in a Pinus radiata nursery with a natural infestation of the pathogen. For nursery trials, the isolates were selected according to in vitro and field trial pathogen controls. The bacteria were applied as seed treatments and via water irrigation. The trials were conduced in a completely randomized block design. Among 568 bacterial isolates tested in vitro, 19.8% displayed some capacity to inhibit the mycelial growth of M. phaseolina, with inhibition between 1.7% and 67.6%. In the first nursery trial, Bacillus amyloliquefaciens VII 015, Bacillus pumilus IX 030, Bacillus stearothermophilus TM 008 and other two Bacillus sp. (VI 009 and IX 049) strains, significantly reduced the total, pre- and post-emergency mortality of seedlings, but no isolate reduced the incidence of M. phaseolina in seedlings. In the second trial, Bacillus sp. IX 049, VI 099, B. subtilis (IX 007) and a non-identified isolate V 005, decreased the incidence of charcoal root rot. It is concluded that the best of these bacterial antagonists have the potential to control M. phaseolina in P. radiata nurseries.