Biological Control of Plant Pathogens, Pests and Weeds Historical Background

History of biological control of plant pathogens dates back to 1900s when Potter (1908) demonstrated the inhibition in activity of plant pathogens by an accumulation of its own metabolic compounds. Sanford (1926) suggested the control of potato scab by green manuring. He proposed two concepts for disease control (a) saprophytic microorganisms can control the activity of plant pathogens, and (b) the microbial balance of soil can be changed by altering the soil conditions.

Addition of fresh organic material will promote the activity and multiplication of saprophytes which by competition for nutrients and oxygen, and by their excretion will depress the activity and multiplication of the pathogens. Millard and Taylor (1927) also reported the control of scab of potatoes grown in sterilized soil inoculated with Streptomyces scabies through simultaneous inoculation of the soil with S. praecox, a vigorous saprophyte. Sanford and Broadfoot (1931) then provided an experimental evidence for Sanford's original hypothesis and demonstrated that infection of wheat seedlings by Ophiobolus graminis in sterilized soil could be completely suppressed by antagonistic action of various individually co-inoculated species of fungi and bacteria.

Weindling (1932) reported the parasitation by Trichoderma viride of many soil fungi. Control of rhizoctonia damping off of citrus seedlings has also been reported by Weindling and Emerson (1936).

Significance of antibiotic production by soil micro-organisms and their possible role in biological control by antibiosis and fungistasis have been discussed by Garrett (1956), Lingappa and Lockwood (1961); Jackson (1965), and Dwivedi and Saravanamuthu (1985).

In recent years, significant researches done on mycoparasitism, mycophagy, nematophagy and antibiosis have led to rapid development of training of antagonists to be applied in biological control of plant pathogens/disease in many ways (Cook, 1977; Old, 1977; Chakraborty et al, 1983; Elad et al, 1984; Manocha, 1985; Dwivedi, 1986).

Table 13.1. Types of antagonists.