Introduction

Vegetable crops may be produced as both fresh market and processed commodities and can be grown under field conditions or in controlled environments, such as glasshouses or other similar structures. There are numerous fungal diseases that attack a wide range of these vegetable crops (Howard et al. 1994), thereby reducing crop yield and quality. Methods for disease control have included the use of cultural practices to reduce pathogen inoculum and disease incidence, development of resistant cultivars, as well as the application of chemical fungicides to inhibit pathogen development. The use of biological control strategies has also demonstrated the potential of fungi and yeasts in reducing a range of fungal pathogens that cause various diseases on vegetable crops.

In this chapter, some examples of recent successes in biological control of fungal diseases of vegetable crops using fungi and yeasts, and the mechanisms by which pathogen control was achieved will be reviewed. In addition, the utilization of techniques in biotechnology to aid in the implementation of biological control strategies for disease control will be reviewed. These include techniques to investigate mechanism(s) of action of the biological control agent, development of strains with enhanced efficacy through genetic manipulation, monitoring the growth and spread of biocontrol agents using molecular techniques, and characterization of strains using genetic markers and biochemical methods.

The diseases to be considered in this chapter for which biocontrol strategies have been described include those caused by pathogenic fungi that infect the seed and early stages of seedling growth, causing seed decay and damping-off. Examples of these fungi are Rhizoctonia solani Kiihn, various species of Fusarium and Pythium, and Sclerotium rolfsii Sacc. Fungal pathogens that infect the roots and crown of developing plants, causing root and crown rots and vascular wilts, have also been researched for biological control strategies. These include fungi such as Pythium spp., Fusarium spp., and Sclerotinia sclero-tiorum (Lib.) de Bary. A third group of foliar-infecting fungi of vegetable crops that cause leaf spots and blights and stem infection, also have biological control strategies developed against them. These include Botrytis cinerea Pers. ex Fr. (gray mold), Didymella bryoniae (Auersw.) Rhem (gummy stem blight), S. sclerotiorum (white mold), and Sphaerotheca and Erysiphe spp. (powdery mildews).

Many different fungal and yeast biological control agents have been identified and evaluated for disease control potential against the above-mentioned pathogens, and some have been formulated and brought to market to provide disease control options for producers of vegetable crops. The use of biological control agents may be particularly attractive for vegetable crops grown in glasshouses, due to the high market value of these crops and the possibility for control of environmental parameters, particularly temperature and relative humidity (Paulitz and Belanger 2001). These are important variables that can significantly influence the efficacy of biological control agents under natural field conditions (Paulitz 1997). The rationale for development of biological control agents against fungal diseases on vegetable crops was to provide an additional/alternative approach to augment/replace the use of chemical fungicides, to provide a level of disease control in the absence of crop genetic resistance, and to augment cultural control practices to further minimize the impact of these diseases and reduce chemical residues in food. For example, chemical fungicides typically have provided adequate control of many fungal pathogens. However, fungicide resistance problems, concerns regarding pesticide residues, and revocation of registration of certain widely-used fungicides, have led to increased activity in the development of biocontrol agents against foliar fungal pathogens.

For a potential biological control agent to reach the stage of commercial deployment, numerous criteria have to be satisfied and considerable data need to be obtained to demonstrate aspects of efficacy, survival, adaptability, and scale-up. These aspects are reviewed elsewhere (Avis et al. 2001a; Cook 1993; Harman 2000; Lumsden et al. 1996) and will not be discussed in this chapter. Several agricultural chemical companies and a number of companies with specialized agricultural products have invested in the discovery and development of biological control agents to complement synthetic pesticides for the control of diseases on horticultural crops. These products are targeted to markets where they have the best chance of performing and where there is the most need, e.g., for control of seed and root-infecting pathogens on seedlings (Whipps 2001). A range of commercially available biological control products for plant disease control is now available (Fravel 2000) and are more likely to be brought to market in the future. Molecular methods have been described that can be adapted for use to ensure quality control and monitoring of the biocontrol agents (Avis et al. 2001a).

Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment