CONTROL OF FUNGAL PLANT PATHOGENS BY MYCOFUNGICIDES -
The species of the genus Trichoderma have become the most widely investigated of all potential mycofungicides. Modern approaches to the use of this fungus to control pathogenic fungi have largely been based on the direct use of inoculants.
Spares of Trichoderma species can be readily & economically produced in the laboratory. But, the fact that no spectacular success has been achieved following the use of Trichoderma as an agent to control fungal pathogen, suggests that either members of this genus are not particularly efficient under field conditions, or more probably that we are not using them to best advantage. Safe & effective biocontrol results have been achieved with Trichoderma under very specialized conditions.
BIOLOGICAL CONTROL -
The use of chemical pesticides, has led to dramatic improvements in the production of crop plants. Since such improvements provided a reliable supply of cheap food they were initially welcomed of late, consumers are becoming increasingly concerned both about food quality & of the real & imagined effects of modern farming methods on the natural environment. While many of these fears have been exaggerated, there is neverthless a developing concensus that modern petro-chemical based farming is ultimately non-sustainable, as a result, more ecological approaches to food production are now being researched.
Pesticides were originally based on toxic heavy metals such as arsenic, mercury, lead or copper. Modern pesticides, however, are organic compounds, with a high degree of specificity towards their target organism. They also generally exhibit low over all toxicity & have little immediate impact on the environment. It is possible that the long term effects of these compounds might be subtly detrimental to soil fertility. Despite the positive results of the use of modern pesticides, concern continues to be expressed about the wisdom of using large quantities of chemicals in the environment. These fears have led biotechnologists to examine alternatives to chemical pesticides as a means of controlling agricultural pests. The most obvious, and apparently environment- friendly, alternative to pesticides is to use naturally occuring biological approaches to the control of pest populations.
Since all pests have natural antagonists, biological control should in theory be relatively straightforward. In practice, successful biological control is extremely difficult to achieve.
Fungi possess a number of characteristics that make them potentially ideal biocontrol agents. Firstly, many saprophytic species antagonise, representatives of all the pest organisms, including plant pathogenic fungi, weeds & insects secondly, fungi can be readily grown in culture so that large quantities can be economically produced for release, mainly as spores or mycelial fragments, into the environment. These inoculants then germinate or grow to produce active mycelium which can parasitise or otherwise inhibit the pest without damaging the non-target organisms. Fungi also survive for relatively long periods as resting bodies, and can then germinate to grow & control the target population thereby making continual reinoculation with the biocontrol agent unnecessary.
Table – Examples of biocontrol agents used commercially or in near commercial condition against soil borne or root-infecting pathogens. Control agent Disease Crop 1. Trichoderma harzianum White rot Onion 2. Phlebia gigantea Heterbasidion root rot Pine 3. Agrobacterium radiobactor var. radiobactor Crown gall Rose 4. Sporidesmium sclerotivorum Lettuce drop Lettuce 5. Talaromyces flavus Damping off Sugarbeet