Manual Biocontrol Agents Pdf To Word
FUNGI AS PARASITESTOPA.Beneficial Fungal Parasites1.Fungi as Biocontrol AgentsTwo of themain areas in which parasitic fungi are beneficial to man are in the useof fungi to control pests and in the prevention of herbivory in plants.1.Biocontrol of Pests:Biocontrolis the reduction of the amount of inoculum or disease producing activityof a pathogen accomplished by or through one or more organisms other thanman. Biocontrol uses natural or modified organisms, genes or gene productsto reduce the effects of undesirable pests and to favor desirableorganisms such as crops, trees, animals and beneficial insects andmicroorganisms.The prime tactics used in biocontrol involve (1) modifying culturalpractices to favor antagonistic plant pathogens, (2) introducingantagonists of plant pathogens into the environment or onto the plant, and(3) inoculate the plant with incompatible or hypovirulent organisms.a. Fungi to Control Plant Diseases:Twoyeasts have been pinpointed that produce killer toxins that block thegrowth of other yeasts (Ag. Res., June 1992, USDA). The yeast, Pichia inositovora and P.acaciae, have been shown to produce antifungal cytotoxic proteins thatwill inhibit the growth of a number of other yeasts. This phenomenon hasbeen put to work where toxins of Kluyveromyceslactis fights against unwanted yeasts that may contaminate fermenting“sake” or rice wine. Species of Trichodermaare used to control root diseases of many crops, stem blight of peanuts,dry bubble on mushrooms, and silverleaf of plums, Verticilliumto control cotton wilt, Sphaerellopsisto control rust diseases on a number of plants, and several others.
Thesebelong to an array of mycofungicides. Prime examples of some aregiven below:Chestnutblight,caused by the perithecial fungus Cryphonectriaparasitica, entered the U.S. On European chestnut timber brought into lumber millsin New England. The fungus was extremely virulent to North Americanchestnuts that had never been exposed to the fungus. Chestnuts were thenthe dominant hardwood lumber tree in this country. The pathogen spreadfirst into New York, being first detected on chestnuts at the New YorkBotanical Garden in 1904.
It soon spread throughout the range of theAmerican chestnut into the southern Smoky Mountains where by 1935essentially all trees had been killed (Fig. A chestnut tree that was killed in the 1920s by Cryphonectriaparasitica, the chestnut blight fungus.Insubsequent years, efforts to find a control for this fungus werefruitless. A biological control imported from Europe in 1972 allows us tokeep American chestnut trees alive. Strains of C.parasitica from Europe were shown to hypovirulent,i. Lower virulence that the native strains. It was initially shown thatthe hypovirulent strain, once inoculated onto a tree diseased with thenative strain, would dominate and suppress the virulence of the nativestrain, thus allowing the American chestnut trees to survive and grow (Fig.10-2).Fig.10-02. Canker on a young chestnut tree caused by the chestnut blightfungus.Severaldifferent hypovirulent strains of C.
Parasitica were tested fortheir ability to dominate the virulent strain (Fig. Several hypovirulent strains of Cryphonectria parasitica. ( Photoprovided by Sandra Anagnostakis)Themost promising ones were inoculated into existing infected chestnut trees(Fig. Inoculating chestnut seedlings with a hypovirulent strain of thechestnut blight fungus. ( Photoprovided by Sandra Anagnostakis)Itwas later shown that the hypovirulence in certain strains was the resultsof a viral infection of the fungus (Anagnostakis & Hillman, 1992.Arnoldia 52:3-9).Root rot ofConifers,caused by Heterobasidium annosum,is a devastating disease of southeastern yellow pines.The disease is spread largely through infestation of freshly cut stumps ofpines, the spread of the fungus into the decaying stump and into the roots. Through natural root grafts,the fungus may be spread throughout a large area (Fig. Root rot of pine caused by the bracket fungus Heterobasidium annosum.Thisdisease may be controlled by treating the surface of cut pine stumps witha spore suspension of Phlebiagigantea.
Colonization of stump surfaces by P.gigantea prevents subsequent colonization by H. Annosum.Post-harvestrot of citrus fruit is caused by species of Penicillium,commonly P. Biocontrol of this problem can beaccomplished by applying the yeast, Pichia guillermondii to fruitafter harvest but before storage or shipping. Pichia inoculatedfruits are shown on the right (Fig. 10-6) and uninoculated on theleft.Fig.10-6.
Fruit rot of citrus showing the effectiveness of biocontrol with Pichia guillermondii(U.S.-7).Brownrot of peach or other stone fruits such as plums, apricots, andcherries is caused by the discomycete Monilinia fruticola and canbe a major problem during rainy seasons, often causing total crop losses. Benomylis the common fungicide used to control brown rot.
The disease, however,may be controlled by inoculating the fruits with the bacterium Bacillussubtilis after harvest but before storage or shipping.This bacterium produces anantifungal metabolite that is toxic to M. 10-7 compares the effectiveness of biocontrol to that of benomyl.Fig.10-7. Biocontrol of brown rot of peach comparing Bacillus subtiluswith the fungicide Benomyl.Damping-offaffects seeds, seedlings, and succulent roots of many plants.
Losses canbe great in moist soils when temperatures are low. Damping offof cotton is caused be the Oomycete Pythium ultimum.
A biocontroltactic used is to treat soil with the fungus Gliocladium virensbefore planting the cotton seed. The production of the antifungalcompound, gliovirin, plays an important role in the control ofdamping-off. This fungus hasalso been used in the control of another important root pathogen, Rhizoctoniasolani.Verticilliumwilt of potato is caused by Verticillium dahliae.
A biocontrolpractice used on this disease is to modify cultural practices to stimulateantagonists or competitors of. Dahliae.Crop rotation and solarization helps the soil to become suppressive to Verticillium.b.Biocontrol of Insects:The knowledge of entomogenous fungi dates back for several centuries(McCoy et al. InIgnoffo, Handbook of Natural Pesticides. CRC Press, Boca Raton, FL).Numerous groups of entomogenous fungi were described during the 19thcentury. Pasteur (1874. 79:1233), however, was one of thefirst to suggest that microorganisms could be used to control insectpests.
Extensive research on the use of Beauvariato control chinch bugs in Kansas had mixed success (Snow, 1896.Ann. One of the earliest successes in biocontrolwas the use of Aschersonia aleyrodesto control citrus white flies in Florida (Berger, 1921.
Manual Biocontrol Agents Pdf To Word Document
More than three decades ago, Rachael Carson's SilentSprings pointed out the dangerous effects of a number of our mosteffective pesticides. This eventually led to the prohibition of the use ofchlorinated hydrocarbons as insecticides. Her book sparked considerableinterest in finding alternative ways of controlling insects. By the 1960sthere were a number of attempts for the commercial production of fungi forbiological control.
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Close to 750 species of entomogenous fungi had beenidentified by the 1980s (Microbial Biocontrol Agents. Sci.Washington, DC, 1979). Almost all of the major groups of fungi have entomogenousspecies, many of them have been used as mycoinsecticides.(Ithank Dr.