Biotic and abiotic factors associated with soil suppressiveness to Rhizoctonia solani

Abstract

Crop management may modify soil characteristics, and as a consequence, alter incidence of diseases caused by soilborne pathogens. This study evaluated the suppressiveness to R. solani in 59 soil samples from a microbasin. Soil sampling areas included undisturbed forest, pasture and fallow ground areas, annual crops, perennial crops, and ploughed soil. The soil samples were characterized according to abiotic variables (pH; electrical conductivity; organic matter content; N total; P; K; Ca; Mg; Al; H; S; Na; Fe; Mn; Cu; Zn; B; cation exchange capacity; sum of bases and base saturation) and biotic variables (total microbial activity evaluated by the CO 2 evolution and fluorescein diacetate hydrolysis; culturable bacterial, fungal, actinomycetes, protozoa, fluorescent Pseudomonas and Fusarium spp. communities). The contribution and relationships of these variables to suppression to R. solani were assessed by path analysis. When all samples were analyzed together, only abiotic variables correlated with suppression of R. solani, but the entire set of variables explained only 51% of the total variation. However, when samples were grouped and analyzed by vegetation cover, the set of evaluated variables in all cases accounted for more than 90% of the variation in suppression of the pathogen. In highly suppressive soils of forest and pasture/ fallow ground areas, several abiotic variables and fluorescein diacetate hydrolysis correlated with suppression of R. solani and the set of variables explained more than 98% of suppressiveness. Key words: soilborne pathogen, soil microorganisms, biological control, path analysis, suppressive soil FATORES BIÓTICOS E ABIÓTICOS ASSOCIADOS À SUPRESSIVIDADE DE SOLOS A Rhizoctonia solaniRESUMO: As atividades agrícolas podem modificar as características do solo e, como conseqüência, alterar a incidência de patógenos veiculados pelo solo. Este trabalho avaliou a supressividade a R. solani em 59 amostras de solos de uma microbacia. As áreas amostradas foram selecionadas quanto à vegetação, incluindo mata, pasto/pousio, culturas anuais, culturas perenes e solo arado. As amostras de solo foram caracterizadas quanto às propriedades abióticas (pH, condutividade elétrica, teor de matéria orgânica, N total, P, K, Ca, Mg, Al, H, S, Na, Fe, Mn, Cu, Zn, B, capacidade de troca catiônica, soma de bases e saturação de bases) e bióticas (atividade microbiana do solo, avaliada pelo desprendimento de CO 2 e hidrólise de diacetato de fluoresceína; comunidades de bactérias, fungos, actinomicetos, protozoários, Pseudomonas fluorescentes e Fusarium spp.

Tropical agriculture and global warming: impacts and mitigation options

“…Climate change as a driver will have different effects on the various types of pests (Garrett et al, 2006;Ghini & Morandi, 2006). Based on studies of individual species, climate change may affect: pest developmental rates and numbers of pest generations per year; pest mortality due to cold and freezing during winter months; or host plant susceptibility to pests (Burdon et al, 2006).…”

“…When two or more species contribute to a pest problem, as with vectored pathogens or pathogens which cause more severe symptoms in the presence of simultaneous insect damage, the effects of climate change could be expressed through any of these species (Ghini, 2005;Garrett et al, 2006). Overall temperature increases may influence crop pathogen interactions by speeding up pathogen growth rates, which increases reproductive generations per crop cycle (Ghini & Morandi, 2006), by decreasing pathogen mortality due to cold winter temperatures, and by effects on the crop itself that leave the crop more vulnerable (FAO, 2005).…”

“…Food production can suffer from climate change impacts such as alteration in solar radiation period and extreme weather events (IPCC, 2001;Overpeck & Cole, 2006). Secondly, the illegal and random deforestation reduces crop production by jeopardizing environmental services such as crop pollination, genetic resources, clean air and water supplies (Foley et al, 2005), soil fertility and erosion (Bertol et al, 2005), pests and pathogen controls that help to maintain crop production (Ghini & Morandi, 2006).…”

<b>Agrosilvopastoral system enhances suppressiveness to soybean damping-off caused by <i>Rhizoctonia solani</i> and alters <i>Fusarium </i>and <i>Trichoderma</i> population density

“…It is difficult to distinguish between primary and secondary factors that are responsible for suppressiveness, what makes difficult the extrapolation or generalizations of the results obtained when only one situation is studied (Höper & Alabouvette, 1996). Soil suppressiveness result from biotic and abiotic factors, in a diverse and complex set of mechanisms, and the contributing factors normally work interactively, requiring a holistic approach to studying it (Ghini & Morandi, 2006).…”

Use of Crape Myrtle,Lagerstroemia(Myrtales: Lythraceae), Cultivars as a Pollen Source by Native and Non-Native Bees (Hymenoptera: Apidae) in Quincy, Florida

“…It is expected that climate change will affect various types of pests in different ways (Garrett et al 2006;Ghini and Morandi 2006). …”