Structural analysis of the inhibition of Pyrenophora teres by Laetisaria arvalis

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Integration of Biological and Chemical Controls for Rhizoctonia Aerial Blight and Root Rot of Rosemary

Aerial blight, caused by Rhizoctonia solani AG-4, was identified as a major disease of greenhouse mist-produced rosemary cuttings. An isolate of the biocontrol fungus Laetisaria arvalis, selected for tolerance to the experimental fungicide CGA 173506, was used as an amendment to potting soil. Combined treatment of rosemary with L. arvalis and a foliar spray of the fungicide at one-half the recommended rate reduced disease more than treatment with either the fungus or fungicide alone. Similar synergism was not observed for combinations of Trichoderma harzianum as a soil amendment and a foliar spray of the fungicide iprodione applied at the labeled rate.

EFFECTS OF RHIZOCTONIA SOLAM DENSITY IN POTTING SOIL ON EFFICACY OF BIOLOGICAL AND CHEMICAL TREATMENTS IN ROSEMARY PROPAGATION

Aerial blight of rosemary (Rosemarinus officinalis) caused by Rhizoctonia solani (AG-4) is a problem in production of rooted cuttings. Two separate studies were conducted on rosemary cuttings during propagation. Four levels of R. solani were mixed into potting medium at the rates of 0, 0.01, 0.1 and 1.0 percent (w/w). Seven treatments were evaluated: Trichoderma harzianum alone, Laetisaria arvalis alone, iprodione (single application, full rate), CGA 173506 (single application, full rate), T. harzianum + iprodione (single application, 1/2x rate), L. arvalis + CGA 173506 (single application, 1/2x rate), and a control. Biocontrol agents were mixed into medium at a rate of 5g/kg medium. Mycelial growth began by day four on the medium surface in the 0.1 and 1.0 R. solani levels. By day six, cuttings showed signs of infection. Disease incidence increased with higher levels of R. solani inoculum. At levels 0.01, 0.1 and 1.0, the L. arvalis plus 1/2x rate one time application CGA 173506 and iprodione alone (full rate one time application) gave the best control of aerial blight in both experiments. In the first experiment, iprodione alone and T. harzianum plus 1/2x rate iprodione gave the most root growth at the 0.01, 0.1 and 1.0 R. solani levels. In the second experiment, L. arvalis plus 1/2x rate CGA 173506 gave best root growth. At level 0, treatments were not significantly different in either experiment.

Thallphytic Alleopathy: Isolation and Identification of Laetisaric Acid

Laetisaria arvalis, a soil-dwelling basidiomycete fungus, secretes an allelopathic agent that induces rapid hyphal lysis in several phytopathogenic fungi. The active compound was isolated from chloroform:methanol extracts ofL. arvalismycelia and characterized as a previously unknown hydroxy fatty acid, (Z,Z-9,12-8-hydroxyoctadecadienoic acid.