Mycoinsecticide

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  • Publicado : 6 de junio de 2010
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POTENTIAL AS A MYCOINSECTICIDE
Successful commercial production and use of entomopathogenic fungi as mycoinsecticides for pest control is posible if specific requirements are met (Roberts et al., 1991; Samsinakova et al., 1981).
i. The fungal isolate selected for mass production/commercialization should possess rapid growth, high pathogenicity to the target pests and sporulate abundantly.
ii.A simple medium with cheap and easily available components should be developed. The production procedure should be easy and also deep the production costs low.
iii. Formulations with long shelf-life at room or near room temperatures without any loss in infectivity and viability need to be developed. An 18 month shelf-life is generally recommended for agricultural markets (Couch and Ignoffo, 1981;Feng et al., 1994).
MASS PRODUCTION
The standard method for the production of microorganisms is by fermentation. Several types of fermentation exist. The two most common are submerged and semi-solid fermentation.
• SUBMERGED FERMENTATION
In submerged or deep-tank fermentation the fungi are grown in a fully liquid system which has the advantage of control over the process parameters such astemperature, pH, aeration and dispersion for efficient growth and yield of the infective units. The method is most suitable for scale-up. In submerged fermentation, blastospores are readily produced but loose viability relatively quickly during storage (Kleespies and Zimmerman, 1992; Rombach, 1989) that are similar to aerial conidia in biological characteristics. However, it is believed thatsubmerged condition is likely to depend on the nature of the isolate and easily formulated in oils. Despite the advantages of submerged fermentation some fungi does not yield a satisfactory product. N. rileyi multiplication by submerged fermentation is not feasible since it does not sporulate in liquid medium.
• SEMI-SOLID FERMENTATION
Semi-solid fermentation offers an alternative in which the fungigrow primarily on the wet surface of a solid material often some form of processed cereal grain to which nutritional adjuvants have been added or media of low value such as agricultural waste. This method allows fungi to grow in conditions more similar to the conditions in nature. Conidia are readily mass produced on solid media under aerated conditions. Semi-solid fermentations are relatively easyto develop on a small scale. Scaling them up to the sizes necessary for commercial production presents numerous problems with aeration, agitation, large surface area of shallow media, caking of media after cooling and drying of material for harvesting spores.
N. riley is easily cultured on solid media. Aerial conidia are produced on solid media and, in porphology and infectivity, areindistinguishable from those produced on the surface of insect cadavers as is the case with Beauveria and Metarhizium spp. An addition of 1% yeast extract to crushed sorghum was found to be an ideal substrate with a maximum yield of 1.4 x 109 conidia/g substrate after 8-9 days at 25°C (Vimala Devi, 1994). N. riley could be multiplied on polished rice grains (Silva and Loch, 1987). Boilign the rice grainsbefore sterilization resulted in higher spore yields. Cost-effective multiplication on crushed barley and also a semi-synthetic medium wherein maltose has been replaced with barley extract is also possible. Conidiation of N. riley occurs readily on semi-synthetic media in general. However, only a few isolates sporulate on cereal grains although mycelia growth occurs readily.
• DIPHASIC PRODUCTIONMass production of aerial conidia by a diphasic fermentation i.e., vegetative mycelia production by liquid batch culture followed by surface conidiation of the mycelia on a nutrient or inert carrier (Soper and Ward, 1981) is commonly practiced although it is labour-intensive. The method has been applied for the production of Beauveria bassaina (Maniania, 1993; Rombach et al., 1988) and Metarhizium...
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