Effect of Organic Amendments on Rhizoctonia and Accompanying Microflora in Soil

Abstract

The effect of oat straw, green bean plants, and cellulose on the infection index and saprophytic activity of Rhizoctonia, and the effect of chitin, N-supplemented oat straw, and green cotton plants on the infection index, saprophytic activity, and soil microflora was tested. A modified method for counting Rhizoctonia-antagonistic bacteria, actinomycetes, and fungi was developed. A relationship between efficiency of the amendments in decreasing infection index and in suppressing the saprophytic activity of Rhizoctonia was observed at the end of the experimental period. Decrease in infection index and saprophytic activity was accompanied by increase in counts of general and antagonistic soil microorganisms. This increase was especially pronounced in chitin-amended soil. The possible mechanism of the biological control of Rhizoctonia by chitin is discussed.

Green manures and crop sequences influence alfalfa root rot and pathogen inhibitory activity among soil-borne streptomycetes

“…In contrast, there were few consistent effects of GM on the density of antagonists or the mean inhibition zone size either year of the trial, though sorghumsudangrass-treated soils tended to have greater proportions of antagonists than fallow-treated soils. Furthermore, consistent with previous studies, GM-treated soils had greater streptomycete (OA) and bacterial densities than fallow-treated soils (Henis et al, 1967;L. L. Kinkel, unpublished data;Mazzola et al, 2001;Rouatt and Atkinson, 1950).…”

“…Green manures may also affect soil-borne pathogens indirectly by influencing indigenous microbial populations. For example, incorporation of soil amendments has been shown to increase soil microbial activity (Davis et al, 1994), microbial diversity (Lupwayi et al, 1998), as well as densities of bacteria (Henis et al, 1967;Mazzola et al, 2001;Rouatt and Atkinson, 1950), fluorescent Pseudomonas spp. (Bulluck and Ristaino, 2002;Conn and Lazarovits, 1999;Mazzola et al, 2001), non-pathogenic Fusarium spp.…”

“…(Bulluck and Ristaino, 2002;Conn and Lazarovits, 1999;Mazzola et al, 2001), non-pathogenic Fusarium spp. (Davis et al, 1994), mycophagous organisms (Scholte and Lootsma, 1998) and streptomycetes and other actinomycetes (Henis et al, 1967;Kinkel et al, 2001;Mazzola et al, 2001) in soil. These changes in the microbial community may affect pathogen populations through competition, parasitism, predation or antagonism (Hornby, 1983;Millard and Taylor, 1927;Scholte and Lootsma, 1998;Weinhold and Bowman, 1968).…”

Enhancement of soil suppressiveness against Rhizoctonia solani in sugar beet by organic amendments

“…Amending the soil with chitin or yeast to suppress Rhizoctonia disease in radish and bean was described by Henis et al (1967Henis et al ( , 1979. Substantial numbers of experiments followed with chitin amendments stimulating disease suppression of different soilborne fungi and nematodes (Hallmann et al, 1999;Mian et al, 1982).…”

Cloning and conjugational transfer of chitinase encoding genes

“…Addition of organic chitin containing amendments to soil have been shown to reduce diseases caused by fungi (Papavizas and Davey 1960, Mitchell and Alexander 1961, 1962, Henis et al 1967, Sneh et al 1971, Sneh 1981). …”