دانلود رایگان مقاله روش تقسیم آگار از متابولیت های میکروبی خاک ضد قارچ

abstract

Soil microorganisms suppress soil borne plant pathogenic fungi through various mechanisms. There is no appropriate, integrated method to easily quantify soil health in terms of disease control ability. A novel assay to quantify the ability of soil to inhibit fungal pathogens is described. The technique is easy to use routinely in soil biology investigations for soil quality testing as it offers an integrated expression of suppressiveness as actidione equivalents per gram of soil. Soil samples were inoculated into liquid growth medium and incubated; supernatants were filter sterilized and assayed in split agar against Macrophomina phaseolina to record colony radius. The antifungal activity of the soils varied widely ranging from 0.02 to 2.80 mg actidione equivalents g
1 soil, of which 81–98% was heat labile. The test will be a useful aid in decision support for reducing the use of chemical control agents and promote sustainable farming practices.

4. Discussion

Soil fungistasis is the ability of soils to inhibit the growth of fungal propagules. Many workers have used indirect methods for enumeration of fungal antagonists in soils like enumeration of fluorescent pseudomonads (Mazzola, 2007) or assessed the community structure of soils (Pereira et al. 2009). Direct methods include estimation of volatile fungistatic compounds either produced by pure isolates of microorganisms from soils (Fernando et al. 2005) or produced from soils directly (Chuankun et al. 2004). The present method is a simple one to estimate the antifungal capacity of soil microorganisms and also offers a convenient mode of quantitative expression of the antibiosis potential as actidione equivalents. The soils tested exhibited varied antifungal abilities. The quantity of antifungal metabolites produced varied widely over a 100 fold range among the samples (Table 1). The range indicates that the method is sensitive to detect small amounts of antifungal compounds produced by soil microorganisms. The pH of the broth incubated with different soils was in a similar range (8.5-8.8), although they showed varying antifungal activities. With some of the broth supernatants, the growth of the fungus tested was similar to that of the blank (uninoculated sterile growth medium) thus showing that pH differences are not responsible for the observed effects which were only due to anti-fungal compounds elaborated.