Severity Of Soil-borne Diseases Research Articles

Biotic and abiotic responses to soilborne pathogens and environmental predictors of soil health

Soilborne pathogens affect agricultural productivity and soil functions, yet the specific impacts of pathogen infections on the soil and plant root-associated microbiomes, the key determinants of plant health, remain unclear. Filling this knowledge gap is required to understanding microbial ecological responses, and to developing biological tools to manage and predict the prevalence and severity of soilborne diseases, which can improve soil health, and plant yield. We hypothesized that soilborne pathogens impact the diversity, function, and ecological interactions in soil microbiomes and form a pathobiome. To test the hypothesis, we conducted field sampling in 35 cotton fields in Australia and collected a total of 560 soil samples, which included samples from the rhizosphere (the area in close contact with the roots) and bulk soils. We aimed to investigate how soil microbiomes and key soil properties respond to Verticillium wilt (VW) of cotton, which is caused by the soilborne pathogen Verticillium dahliae. We found that the presence of the pathogen altered the microbiome structure in both bulk and rhizosphere soils. Notably, healthy soils exhibited more complex microbial networks than diseased soils. Furthermore, a putative pathobiome consisting of various microbial taxa that could influence pathogen infection was identified. Specific pathobiome taxa, such as Gibellulopsis spp., displayed a positive association with V. dahliae. In contrast, known biocontrol agents (BCAs) such as Bacillus spp., Fusarium spp., and Talaromyces spp., were negatively correlated with pathogen abundance. After isolation, pathobiome BCA members demonstrated strong biocontrol activity against V. dahliae in vitro, indicating their potential for enhancing resistance to pathogen invasion in agricultural soils. Moreover, shotgun sequencing analysis revealed a gene encoding beta-glucosidase as a putative indicator of soil health. Structural Equation Modelling showed that VW disease incidence is significantly influenced by several factors, including the relative abundance of V. dahliae, the pathobiome, and various abiotic factors such as precipitation, soil moisture, and pH. Taken together, our findings offer novel field evidence for the key biotic and abiotic drivers of a soilborne pathogen. This knowledge could facilitate the development of biological tools to control soilborne diseases and predict soil health and disease incidence, thus providing innovative strategies for sustainable agricultural disease management.

Agronomic and phytosanitary characterization of tomato production in the Comiteca- Tojolabal Plateau

Objective: To characterize the agronomic and phytosanitary aspects of the tomato production units of the Comiteca-Tojolabal Plateau, Chiapas, Mexico.Design/Methodology/Approach: A random sampling of n=76 tomato fields was performed; agronomic practice surveys were applied to their respective farmers, and the phytosanitary status of each site was evaluated.Results: Tomatoes are grown in shade houses, in plots that mostly do not exceed 0.5 ha. The most common practices are crop rotation, one tomato cycle per year, incorporation of previous crop residues, and fertilization every 5-8 days. For phytosanitary management, foliar sprays are usually performed every 5-8 days. In order to prevent diseases and pests, 67% of producers pre-treat seedlings and 95% apply bactericides and fungicides to the roots during the first 45 days of the crop. The most important pests and diseases are whitefly, thrips, Bactericera sp., late blight, virosis, and wilt. The percentage of plants that suffer from root and vascular diseases ranges from 0-38%. However, low values were more frequent. The regional severity of wilting is low, since 90% of the plants evaluated did not present symptoms. Study Limitations/Implications: This is the first work to describe the agronomic and phytosanitary aspects of tomato cultivation in this region. Additional research with this approach is required and this work will be the basis for further studies.Findings/Conclusions: Most of the tomato farms have less than 0.5 ha and their farmers carry out intensive phytosanitary management with pesticides. In addition to chemical control, the cultural practices used may contribute to a low incidence and severity of soil-borne diseases. The most important crop diseases are late blight and virosis.

Responses of soybean, Glycine max (L.) Merr. to dolomite and calcite fertilization in an upland field converted from a paddy field

ABSTRACT Dolomite [CaMg(CO3)2] is used widely for soybean, Glycine max (L.) Merr. production in Japan to amend soil pH, although magnesium (Mg) in the dolomite can inhibit soybean growth and yield. The aim of this study was to determine the effect of Mg on soybean production in a paddy – upland rotation field in 2019–2020 by comparing the application of dolomite and calcite (CaCO3). The field test included three replications with three lime applications: control (no lime), dolomite, and calcite. The amounts of calcite and dolomite applied in each year were 253 and 259 g m−2, respectively. The soil pH was almost similar following the applications of calcite and dolomite, whereas the soil exchangeable Mg content was higher following the dolomite application than following the other applications. The shoot weight from the flowering stage to the harvest stage (R8) was significantly higher following the calcite application than following the other applications. However, the shoot weight at only R8 was significantly higher following the dolomite application than following the control application. In 2019–2020, the highest soybean yield was resulted from the calcite application (355 g m−2) followed by the dolomite application (312 g m−2) and the control application (260 g m−2). The severity of soil-borne diseases was lower following the dolomite application than following the control application, and even lower following the calcite application. Thus, the application of dolomite increased soybean yield by improving soil pH; however, Mg in the dolomite inhibited a further increase in soybean yield in a paddy – upland rotation field.

Seasonal variations in the composition and diversity of rhizosphere soil microbiome of bamboo plants as infected by soil-borne pathogen and screening of associated antagonistic strains

As the occurrence and severity of soil-borne diseases are strongly season-dependent, the ecological processes that shift plant microbiome compositions and functions upon pathogen infection in different seasons are rarely studied. In this study, we compared the differences in fungal and bacterial communities in rhizosphere soil between healthy and diseased bamboo plants throughout the four seasons at the main bamboo production site in China and investigated how basal rot disease caused by Fusarium proliferatum affected the composition, structure and ecological functions of rhizosphere-associated microorganisms. The results showed that diseased bamboo plants enriched the highest abundance of Fusarium genus in rhizosphere soil while receiving largely increased stem lesion area in summer. Microbiome analysis further proved that healthy bamboo plants harbored more ecologically beneficial microbial taxa that might function as biological protectants in their rhizosphere soil than diseased plants at the same season. Three individual strains with biocontrol potentials were further isolated and identified as Trichoderma spirale, Bacillus velezensis and Streptomyces mirabilis. The antagonistic tests further demonstrated their inhibition effects on the growth and pathogenicity of the pathogenic fungus F. proliferatum in vitro and in vivo. This study advances our understanding of soil-borne pathogen mediated changes in microbiome structure and function in plant rhizosphere soil and provides potential biocontrol strains for increasing plant resistance against basal rot disease.

Use and Effects of Different Brassica and Other Rotation Crops on Soilborne Diseases and Yield of Potato †

Soilborne diseases are persistent problems in potato production, resulting in reductions in tuber quality and yield. Brassica rotation crops may reduce soilborne potato diseases, but how to best utilize Brassica crops in potato cropping systems has not been established. In this research, two two-year trials were established at three different sites with histories of soilborne diseases, and up to six different Brassica crops (canola, winter rapeseed, yellow and brown condiment mustards, oriental mustard, oilseed radish, and a mustard blend) and standard rotation crops (ryegrass and buckwheat) were evaluated as rotation and green manure crops. Tuber yield did not vary substantially among the rotation crops, but rotation treatments significantly affected incidence and severity of soilborne diseases at all sites. However, results were variable among sites and years. Perennial ryegrass and mustard blend rotations reduced powdery scab disease by 31–55% relative to other rotations in the only field where powdery scab was a serious problem. Mustard blend, ryegrass, and other Brassica rotations also reduced common scab, silver scurf, and black scurf at various sites, but not consistently at all sites. At one site, mustard blend and barley/ryegrass rotations reduced black scurf (by 21–58%) and common scab (by 13–34%) relative to no rotation. Overall, disease control was not correlated with biofumigation potential or rotation crop biomass production. Although both Brassica and non-Brassica rotations provided disease reduction in potato cropping systems, no single rotation crop performed consistently better than several others.

Isolation and characterisation of endophytic actinobacteria and their effect on the early growth and nodulation of lucerne (Medicago sativa L.)

Background and aims Endophytic actinobacteria are known to benefit their hosts by improving plant growth and by reducing the severity of soil borne diseases. In this study, their role in enhancing the growth of lucerne and their interaction with its rhizobial symbiosis is examined. Comparison is made between endophytic actinobacteria isolated from wheat plants and isolates from the roots and nodules of four different legume species: lucerne (Medicago sativa L.), field pea (Pisum sativum L.), subterranean clover (Trifolium subterraneum L.) and burr medic (Medicago polymorpha L.).

The Economic Impacts of Disease Suppressive Rotations in Maine Potato Cropping Systems

Soil borne diseases can greatly reduce marketable yields and are a major concern to Maine potato (Solanum tuberosum L.) producers. Control of these organisms is difficult as they can persist in the soil for several years and symptoms typically worsen each year. Depending on the specific pathogen, different mechanisms for moderating soil borne disease can be employed, such as breaking the hostpathogen cycle, stimulating beneficial microbial activity, and direct inhibition of the pathogens. Current research at the USDA-ARS New England Plant, Soil, and Water Laboratory is investigating the effect of rotation crops and rotation sequences on the incidence and severity of soil-borne diseases in the following potato crop. These results (incidence, severity, and potato yield) are incorporated into an economic simulation model to determine the impact of rotations on profitability, level of income risk, and probability of economic loss for different rotation sequences and rotation lengths. The results show that several rotation sequences can increase profitability and reduce economic risk when compared to continuous potato or to the standard barley-potato rotations.

Prevalence, Incidence and Severity of Soil-borne Diseases and Fungi of Wheat in Rice-wheat Cropping System of Punjab Province of Pakistan During the Cropping Season 1999

Prevalence, Incidence and Severity of Soil-borne Diseases and Fungi of Wheat in Rice-wheat Cropping System of Punjab Province of Pakistan During the Cropping Season 1999

Double-Cropping and Crop Rotation Effects on Diseases and Grain Yield of Pearl Millet

The effects of double-cropping and crop rotation sequences on grain yield and diseases of pearl millet [Pennisetum glaucum (L.) R. Br] were evaluated to determine the compatibility of pearl millet in southeastern agricultural cropping systems. Pearl millet hybrid 'HGM 100' (Agra Tech Seeds, Inc., Atlanta, GA) was planted with minimum tillage, double-cropped with canola (Brassica napus L.) and wheat (Triticum aestivum L.). Soybean [Glycine max (L.) Merr.] was used as an alternative summer annual to pearl millet in rotation sequences. Treatment effects on seedling stand density, panicle number, grain yield, leaf blight (caused by Exserohilum rostratum), stalk and neck rot (associated with a number of fungi), and smut (caused by Moesziomyces penicillariae) severity were determined. Seedling stands 3 wk after planting were lower following canola than wheat in 1995 and 1997, and panicle number was lower in 1997. No other yield-associated variables were affected by the previous winter crop. In comparison of crop rotations, inconsistent effects were observed in stand density in 1997, and panicle number in 1996 and 1997. Seedling stand density and panicle number were lower with 2 yr of pearl millet compared with 1 yr, but were highest for the 3 sequential yr of cultivation in 1997. A trend toward increased smut severity in plots continuously planted to pearl millet was observed in 1997. Within subplots, stand density was highly correlated with panicle number in 1996 and 1997 (r ≥ 0.51, P < 0.01), with leaf blight severity in 1995 and 1996 (r ≥0.33, P < 0.01) and with stalk and neck rot in 1996 (r = 0.60, P < 0.01). Yield was negatively correlated (r ≥ -0.31, P < 0.01) with leaf blight severity in 1995 and 1996, and stalk and neck rot in 1996 (r = -0.46, P < 0.01). Stalk and neck rot in 1996 was probably caused by Fusarium graminearum, which was more commonly isolated from pearl millet following canola than wheat. Neither the previous winter annual crop nor the number of sequential years of pearl millet cultivation had detrimental, limiting effects on pearl millet grain yield or diseases.

Interactions between organic-matter decomposition level and soilborne disease severity

Literature reviewed shows that no-tillage small-grain production increases Rhizoctonia bare-patch disease in arid climates. The type and amount of residues, the method of their incorporation and the level of decomposition at the time of planting appear to affect disease severity. Partially decomposed residues of the previous season confound interpretation of the current season's input. Interactions between organic-matter decomposition level and disease severity in soil systems, therefore, are difficult to resolve. Organic-matter transformations that occur during decomposition of wastes in compost piles are similar to those in soil. This process, therefore, was tested as a model to determine effects of organic-matter decomposition level in soil systems. Both Rhizoctonia solani and its antagonist Trichoderma hamatum developed to high population levels in a substrate amended with fresh organic matter. However, high levels of disease also developed. A negative relationship was found between increasing decomposition levels of the organic matter (compost age) and population development of both the pathogen and its antagonist, as well as with disease severity. On the other hand, addition of high levels of cellulose to this disease-suppressive substrate amended with a mature compost, in amounts equivalent to levels of cellulosic substances present on the surface of soil in no-tillage small-grain production, stimulated population development of both the pathogen and the antagonist and negated the suppressive effect. We conclude that the composting process can be used to examine interactions between specific crop-residue decomposition levels, the host, the pathogen and its biocontrol agents.