|Gracia-Garza, Javier - NC STATE UNIVERSITY|
|Paulitz, Timothy - MCGILL UNIV, QUE, CANADA|
|Reeleder, Richard - AGRI-FOOD, CANADA|
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 1997
Publication Date: N/A
Interpretive Summary: Sclerotinia sclerotiorum is a plant pathogen which causes diseases on many economically important crops. This pathogen produces structures known as sclerotia which allows this fungus to overcome adverse environmental conditions. Sclerotia when germinated produce spores capable of infecting a susceptible host. Destruction of these structures will aid in the control lof the diseases it causes. The use of beneficial organisms to degrade sclerotia was tested in this report. The fungus Trichoderma hamatum and the larvae of fungus gnats (Bradysia coprophila) parasitize and predate on, respectively, sclerotia, reducing its potential to germinate. When sclerotia damaged by the feeding activity of fungus gnats were buried in soil infested with T. hamatum it was observed that they were degraded more rapidly than sclerotia damaged by mechanical means. Heavily damaged sclerotia by larvae feeding enhanced the growth of T. hamatum. Exudates from sclerotia whose outer layers were removed by the larvae accelerated the germination of spores of T. hamatum. Larval damage changed the sclerotium physically and chemically, enhancing the activity of T. hamatum. The use of chemical products to control plant pests and diseases is representing an increasing hazard to the environment. Control of plant diseases using beneficial organisms, as those explored in this research, will aid in the establishment of more environmentally friendly methods of disease control by growers of agricultural products. Scientists will also benefit from these findings in their understanding of these complex interactions.
Technical Abstract: Damaged sclerotia of Sclerotinia sclerotiorum buried in soil infested with Trichoderma hamatum isolate TMCS 3 were degraded rapidly when the medulla of sclerotia was completely exposed by the feeding activity of larvae of the fungus gnat Bradysia coprophila. These heavily damaged sclerotia also enhanced, in vitro, the growth of TMCS 3. Growth of TMCS 3 in liquid culture was studied using different carbon sources as substrates, includin sclerotia of S. sclerotiorum. Significantly more biomass of TMCS 3 was recovered using sclerotia as a substrate compared to other carbon sources tested. Exudates from sclerotia whose melanized rinds had been completely removed by feeding larvae accelerated the germination of conidia of TMCS 3. Concentrations of amino acids, carbohydrates, and proteins in the sclerotial exudates were not increased as damage to sclerotia was increased. Exudation of electrolytes was higher in undamaged than damaged sclerotia. Glucanase activity of TMCS 3 was slightly increased when the fungus was exposed to damaged sclerotia. However chitinase activity was not increased by damaging the sclerotia. Larval damage to sclerotia altered not only physically but also chemically the sclerotium enhancing the activity of the fungus Trichoderma hamatum.