Seedling Root Crown and Vascular Wilt Diseases

Gliocladium virens Miller, Giddens and Foster, a biocontrol agent of a wide range of fungal pathogens, is now classified in the genus Trichoderma due to similar morphological characteristics that are shared with members of this genus and DNA analysis supported the inclusion of G. virens with the Trichoderma genus (Rehner and Samuels 1994). One characteristic of G. virens is the ability to produce the antibiotic metabolites gliotoxin and viridin, a characteristic not generally shared with other species of Trichoderma (Papavizas 1985). G. virens (T. virens) strain GL-3 was evaluated as a seed treatment on tomato against several pathogens, including R. solani, P. ultimum, S. rolfsii, and

F. oxysporum f. sp. lycopersici. The treatment resulted in significantly higher seedling establishment (Mao et al. 1998).

A commercial formulation of strain GL-21 of G. virens is registered for use in the United States, under the trade name SoilGard™, and can control P. ultimum and R. solani on vegetables and ornamental seedlings (Koch 1999; Lumsden et al. 1996). Like T. harzianum strain T-22, certain strains of

G. virens have the ability to colonize the rhizosphere of plant roots (Harman 2000). In addition, the production of gliotoxin occurs rapidly (within a few hours) and can persist for several days to provide high levels of pathogen suppression (Lumsden et al. 1992; Wilhite and Straney 1996). Gliotoxin has also been shown to act synergistically with endochitinase in G. virens (Di Pietro et al. 1993).

A related species, G. catenulatum Gilman and E. Abbot, has been reported to be effective in reducing the incidence of damping-off diseases, caused by P. ultimum and R. solani (McQuilken et al. 2001). Incorporation of a wettable powder formulation of G. catenulatum strain JI446 into peat-based growing media or application as a drench reduced damping-off due to P. ultimum and R. solani. Two commercial formulations of G. catenulatum strain J1446 (Prestop and Primastop) have been recently developed (Fravel 2000; Niemi and Lahdenpera 2000). Primastop is currently registered in Europe and in a number of regions of the United States, and Prestop is expected to be registered in the near future (Niemi and Lahdenpera 2000). G. catenulatum strain J1446 was able to colonize cucumber roots extensively 5 weeks following its application, indicating that the fungus has the ability to survive and proliferate in the rhizosphere of plants. This rhizosphere competence, coupled with its reported ability to act as a mycoparasite (McQuilken et al. 2001) makes G. catenulatum a strong candidate as a biological control agent against a number of vegetable diseases. We have evaluated this biocontrol agent against Pythium root and crown rot of cucumber caused by P. aphanidermatum. Application at the time of seeding significantly reduced plant mortality and enhanced seedling growth (Figure 1).

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

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