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Title: Effect of inoculum density and soil tillage on the development and severity of Rhizoctonia root rot

item Paulitz, Timothy

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2007
Publication Date: 3/20/2008
Citation: Schroeder, K.L., Paulitz, T.C. 2008. Effect of inoculum density and soil tillage on the development and severity of Rhizoctonia root rot. Journal of Phytopathology. 98:304-314.

Interpretive Summary: Rhizoctonia bare patch and root rot, caused by various Rhizoctonia spp., can become more severe in no-till systems when tillage is eliminated. We wanted to compare two sets of conventional and no-till soils, to see if they differed in their ability to support disease in the greenhouse, when inoculated with various levels of Rhizoctonia solani and R. oryzae and planted with barley. We also looked at the ability of these two fungi to grow through intact soil cores from these same fields. When soil was removed from the fields, processed, mixed and amended with inoculum, no differences were seen between conventional and no-till soils. However, when the soil structure was intact, the growth rate of hyphae through the soil was influenced by tillage.

Technical Abstract: Rhizoctonia spp. cause substantial yield losses in direct-seeded cereal crops, compared to conventional tillage. To investigate the mechanisms behind this increased disease, soils from tilled or direct-seeded fields were inoculated with Rhizoctonia spp. at population densities from 0.8 to 250 propagules per gram and planted with barley (Hordeum vulgare). The incidence and severity of disease did not differ between soils with different tillage histories. Both R. solani AG-8 and R. oryzae stunted plants at high inoculum densities, with the latter causing pre-emergence damping-off. High inoculum densities of both species stimulated early production of crown roots in barley seedlings. Intact soil cores from these same tilled and direct-seeded fields were used to evaluate the growth of Rhizoctonia spp. from colonized oat seeds. Growth of R. oryzae was not affected by previous tillage history. However, R. solani AG-8 grew more rapidly through soil from a long-term direct-seeded field compared to tilled soils. The differential response between these two experiments (mixed, homogenized soil vs intact soil) suggests that soil structure plays a major role in the proliferation of R. solani AG-8 through soils with different tillage histories.