Organic Transition Effects on Soilborne Diseases of Soybean and Populations of Pseudomonadaceae

Abstract

During transition to organic production, various strategies can be implemented to enhance soil health, including the soil property of disease suppressiveness. We previously found increased levels of diseases caused by biotrophic pathogens associated with manure application, but manure also suppressed diseases caused by necrotrophic pathogens. In an extension of that study we evaluated soils from di erent cropping system and organic amendment treated plots using a bioassay of suppressiveness to two soilborne diseases, Rhizoctonia root rot and sudden death syndrome (SDS) of soybean [Glycine max (L.) Merr.]. Also, the soil population levels of Pseudomonadaceae were assessed for their suitability as an indicator of disease suppressiveness. Levels of soil suppression of both Rhizoctonia root rot and SDS were found to be associated with speci c cropping systems, but the associations were not consistent from year to year. ere were no associations between organic amendment treatments and disease suppression in the bioassay studies. However, there was an overall increase in soil suppressiveness to Rhizoctonia solani during the 3 yr of transition, regardless of cropping system or organic amendment treatments. In contrast, there was an overall decrease in suppressiveness to Fusarium virguliforme during the transition. ere was no signi cant e ect of cropping system or organic amendment treatments on the levels of Pseudomonadaceae, indicating that this was not a good predictor of general suppression in this study. While speci c treatments were not found to consistently impact soil suppressiveness, the overall increase in suppressiveness to R. solani during the 3-yr transition did show the value of the transition process.

Plant disease management in organic farming systems

“…Organic farmers strive for a healthy ecosystem with high biological diversity, minimal nutrient losses and natural buffering capacity against diseases and pests . However, it takes many years for new microbial and chemical equilibria with relative stability to become established after the conversion from CF to OF, and during the transition period, several pest and disease outbreaks may occur …”

“…9,12,95 However, it takes many years for new microbial and chemical equilibria with relative stability to become established after the conversion from CF to OF, and during the transition period, several pest and disease outbreaks may occur. 188,189 Nevertheless, epidemic spread of many plant diseases can be curbed as a result of greater crop diversity in time and space and the use of natural vegetation, barrier and cover crops. After a transition period of about 5 years, soil-borne diseases are commonly suppressed in OF, including fungus-and nematode-transmitted virus diseases, provided crop rotation is sufficiently long.…”

Organically Grown Soybean Production in the USA: Constraints and Management of Pathogens and Insect Pests

“…General suppression makes use of the fact that soils are habitats for many microorganisms, including fungi, bacteria, and nematodes, most of which are not pathogenic on plants and, in fact, are beneficial to plant growth in many ways, including that they can parasitize, compete with, or otherwise suppress plant pathogens. It has been shown that many soilborne plant diseases are more severe when sterilized soils are reinfested with plant pathogens as compared to when the pathogens are added to non-sterilized field soils [23].…”

“…It also has been demonstrated in several cropping systems that additions of organic material, such as composted plants and green manures, can increase the disease suppressive characteristics of soils in some circumstances [23,[32][33][34]. This is not a simple situation, where the addition of any organic material to a soil will result in the suppression of any and all plant diseases.…”

Soybean sudden death syndrome: Fungal pathogenesis and plant response

“…The impact of cropping systems on the natural suppression of F. virguliforme and SDS disease has been investigated. Various cropping system treatments including a perennial pasture system, a cash grain rotation system, and an intensive vegetable production system were conducted over 3 years (Marzano et al, 2015). No effect of these treatments was found on foliar SDS symptoms during years 1 and 3, but the perennial pasture system increased foliar disease severity during year 2 (Marzano et al, 2015).…”