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Myths and Dogmas of Biocontrol Changes in Perceptions Derived from Research on Trichoderma harzinum T-22.

Antagonistic fungi, trichoderma spp.: panoply of biological control

Trichoderma spp. are endophytic plant symbionts that are widely used as seed treatments to control diseases and to enhance plant growth and yield. Although some recent work has been published on their abilities to alleviate abiotic stresses, specific knowledge of mechanisms, abilities to control multiple plant stress factors, their effects on seed and seedlings is lacking. We examined the effects of seed treatment with T. harzianum strain T22 on germination of seed exposed to biotic stress (seed and seedling disease caused by Pythium ultimum) and abiotic stresses (osmotic, salinity, chilling, or heat stress). We also evaluated the ability of the beneficial fungus to overcome physiological stress (poor seed quality induced by seed aging). If seed were not under any of the stresses noted above, T22 generally had little effect upon seedling performance. However, under stress, treated seed germinated consistently faster and more uniformly than untreated seeds whether the stress was osmotic, salt, or suboptimal temperatures. The consistent response to varying stresses suggests a common mechanism through which the plant-fungus association enhances tolerance to a wide range of abiotic stresses as well as biotic stress. A common factor that negatively affects plants under these stress conditions is accumulation of toxic reactive oxygen species (ROS), and we tested the hypothesis that T22 reduced damages resulting from accumulation of ROS in stressed plants. Treatment of seeds reduced accumulation of lipid peroxides in seedlings under osmotic stress or in aged seeds. In addition, we showed that the effect of exogenous application of an antioxidant, glutathione, or application of T22, resulted in a similar positive effect on seed germination under osmotic stress or in aged seed. This evidence supports the model that T. harzianum strain T22 increases seedling vigor and ameliorates stress by inducing physiological protection in plants against oxidative damage.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-10-0091

Seed Treatment with Trichoderma harzianum Alleviates Biotic, Abiotic, and Physiological Stresses in Germinating Seeds and Seedlings

Publisher Summary There has been a large upsurge in interest in biological disease control recently, reflecting increasing environmental concern over pesticide use. This chapter discusses the ecological considerations, which comprises of suppressive soils, organic amendments and cornposts, monoculture decline, physical and chemical practices, and role of fauna in natural biological disease control. There has been a gradual increase in the number of commercial biocontrol agents on the market for the control of soil–borne plant pathogens over the last few years and only one product, Dagger–G, a Pseudomonaspuorescens marketed by Ecogen, Inc, Lanhorne, PA, USA, for the control of Rhizoctonia and Pythium damping–off of cotton, has been withdrawn from sale because of poor shelf–life of the material. The chapter discusses that chemicals still dominate the disease control market and some consideration should be given to research areas likely to improve further the commercial uptake of biological disease control agents. Consequently, optimizing realistic screening procedures is a first step, which can be refined to target specific types of antagonists. Once specific antagonists have been identified, they can be developed further by consideration of inoculum production, formulation, storage and application, ideally linking the expertise of scientific researchers with industrial partners. Molecular biology has helped identify the modes of action of many biocontrol agents. A considerable effort is currently underway to improve biocontrol efficacy of microorganisms through the use of molecular biology.

Developments in the Biological Control of Soil-borne Plant Pathogens

Trichoderma as biostimulant: exploiting the multilevel properties of a plant beneficial fungus

Production of conidial biomass of Trichoderma harzianum for biological control

Conidial Biomass and Desiccation Tolerance of Trichoderma harzianum Produced at Different Medium Water Potentials

Control of plant pathogens has been accomplished in large part by the use of chemical pesticides. Biological control of these plant pathogens was originally thought to be futile (Garrett, 1956); however, many researchers have shown that certain filamentous fungi are capable of controlling several plant pathogenic fungi. These “biofungicides” have been under investigation for several years. Fungi in the genus Trichoderma have been shown to suppress Pythium spp. (Chet et al., 1981; Harman and Hadar, 1983), Sclerotium rolfsii and Sclerotinia sclerotiorum (Lee and Wu, 1984), Rhizoctonia solani (Elad et al., 1980; Harman et al., 1981; Lewis and Papavizas, 1987), Botrytis cinerea (Tronsmo, 1989), and Fusarium spp. (Sivan and Chet, 1986; 1989) and other pathogens (Cook and Baker, 1983) on various agronomically and horticulturally important plants. Diseases caused by these plant pathogens (e.g., seed rots, damping-off, wilts, fruit rots, and root rots) have been shown to be effectively reduced by Trichoderma. This ability is of major importance because of new restrictions on the applications of chemical pesticides (Harman and Lumsden, 1990). Also, the use of chemical fungicides may eliminate a large range of organisms, some of which may be beneficial to the environment. Biocontrol organisms should be less disruptive than chemical pesticides.

X. Jin

Papers

Production of conidial biomass of Trichoderma harzianum for biological control

Conidial Biomass and Desiccation Tolerance of Trichoderma harzianum Produced at Different Medium Water Potentials

Principles in the Development of Biological Control Systems Employing Trichoderma Species Against Soil-Borne Plant Pathogenic Fungi

Development of Media and Automated Liquid Fermentation Methods to Produce Desiccation-Tolerant Propagules ofTrichoderma harzianum

Liquid coating formulation for the application of biological seed treatments of Trichoderma harzianum.