Plant disease represents a significant economic cost to modern agriculture. Current systems of agriculture often require one or a few crops or plant types to be grown over a large area. Such an ecologically unbalanced system is susceptible to disease.
Traditionally, control of plant pathogens such as fungi has been pursued through the use of chemical fungicides or pesticides. However, consumers are becoming increasingly concerned about chemical residues on plants and their effects on the environment. Moreover; pathogens are becoming increasingly resistant to available fungicides and pesticides.
Biological, control represents an alternative means of controlling plant disease which reduces dependence on chemicals. Such “natural” methods enjoy greater public acceptance, and may be more effective and sustainable than chemical control methods.
A wide range of biological control agents including bacteria, yeast and fungi have been investigated for use in controlling plant disease. One mechanism which has been demonstrated to be effective is the use of microbial antagonists such as Trichoderma and Gliocladium species to control plant pathogenic fungi, and to promote plant growth.
Trichoderma is a genus of fungi containing about 20 species of which many have been explored for their biocontrol and growth promotion potential. See for example U.S. Pat. No. 4,748,021, U.S. Pat. No. 4,713,342, U.S. Pat. No. 4,915,944, U.S. Pat. No. 5,084,272, U.S. Pat. No. 5,238,690, U.S. Pat. No. 5,260,213, U.S. Pat. No. 5,266,316, U.S. Pat. No. 5,882,914, U.S. Pat. No. 6,753,295, and U.S. Pat. No. 7,070,984. Trichoderma harzianum in particular is the active component in a number of commercially available products such as PlantShield®, and RootShield® Granules (Bioworks Inc, New York, USA) for suppression of root diseases and growth promotion. Trichoderma viride is an effective biocontrol agent against fusarium wilt in Chrysanthemum (U.S. Pat. No. 4,489,161). Trichoderma viride is also the active component in the commercially available product Trieco® (Ecosense Labs, India), and in the bio-fungicide Sentinel® (Agrimm Technologies Ltd, New Zealand), which is used for control of Botrytis Cinerea on grapes and tomatoes. More recently, combinations of Trichoderma with other fungal and/or bacterial antagonists have been explored for use as broader spectrum biocontrol agents and for plant growth promotion. See for example U.S. Pat. No. 6,808,917, U.S. Pat. No. 6,890,530, US 2002/0103083, US 2004/0261578, WO 2004/054365, WO 2007/110686 and WO 2007/116245.
The efficacy of various Trichoderma species for biocontrol and growth promotion has also been discussed by Stewart et al, Australian Plant Pathology Society, Adelaide, 2007.
Despite extensive investigations into Trichoderma species for biocontrol and growth promotion, very few Trichoderma products are available for commercial use. None are available for use on pasture plants. This is primarily because of the complex interactions that take place in the soil or on plants between Trichoderma and other microorganisms, the environment, and the plant or plant root.
Therefore, while potential biocontrol and plant growth promotion agents with antagonistic characteristics can be found, they must be carefully screened for a range of traits relevant to their proposed use. These traits include plant pathogenicity, antagonistic activity and specificity, amenability to manipulation in delivery systems and formulations, and performance under fluctuating field conditions with target plants. Establishment and performance in the field is often the most difficult challenge to overcome. Any Trichoderma agent must be able to successfully establish and compete with the multitude of existing field microorganisms, in a way, which is not harmful to target plants. Trichoderma combination products present further challenges where all Trichodermas selected for use in a combination must be compatible and not out compete each other under field conditions. Accordingly, there is still a need for new Trichoderma species for use as biocontrol and/or growth promotion agents which address these issues.
The applicants have now identified a number of new Trichoderma atroviride that are highly effective as biocontrol agents and/or growth promotants either alone or in combination.
An object of the invention is therefore to provide novel Trichoderma atroviride strains useful as biocontrol agents or as growth promotants or as both. Another object is to provide a composition comprising at least one of the novel Trichoderma atroviride strains of the invention, a combination of all strains of the invention, or all four strains identified herein; or at least to provide the public with a useful choice.