Pathogen Populations In Soil Research Articles

Parthenium hysterophorus alleviates wilt stress in tomato plants caused by Ralstonia solanacearum through direct antibacterial effect and indirect upregulation of host resistance.

Heavy damage to tomato crops due to wilt stress caused by the pathogenic bacterium Ralstonia solanacearum and the insufficient availability of management strategies with desired control levels urged the researchers to investigate more reliable control methods to manage this issue in tomato and other horticultural crops. In this study, Parthenium hysterophorus, a locally and freely available herbaceous plant, was successfully used to manage bacterial wilt of tomatoes. The significant growth reduction ability of P. hysterophorus leaf extract was recorded in an agar well diffusion test and its ability to severally damage the bacterial cells was confirmed in SEM analysis. In both greenhouse and field trials, soil amended with P. hysterophorus leaf powder at 25 g/kg soil was found to effectively suppress the pathogen population in soil and significantly reduce the wilt severity on tomato plants, resulting in increased growth and yield of tomato plants. P. hysterophorus leaf powder at concentrations greater than 25 g/kg soil caused phytotoxicity in tomato plants. The results showed that P. hysterophorus powder applied through the mixing of soil for a longer period of time before transplanting tomato plants was more effective than mulching application and a shorter period of transplantation. Finally, the indirect effect of P. hysterophorus powder in managing bacterial wilt stress was evaluated using expression analysis of two resistance-related genes, PR2 and TPX. The upregulation of these two resistance-related genes was recorded by the soil application of P. hysterophorus powder. The findings of this study revealed the direct and indirect action mechanisms of P. hysterophorus powder applied to the soil for the management of bacterial wilting stress in tomato plants and provided the basis for including this technique as a safe and effective management strategy in an integrated disease management package.

Control of potato powdery scab (Spongospora subterranea) in Israel with chloropicrin, metam sodium or fluazinam

Powdery scab, caused by Spongospora subterranea, causes significant economic damage in potato production worldwide due to reduced quality and marketability of seed and ware tubers. Three field experiments were conducted in naturally infested soil during winter 2008, 2012 and 2013 to evaluate the efficacy of soil fumigation on powdery scab on tubers, root galling and the pathogen populations in soil. Soil fumigation with metam sodium (MS) or chloropicrin (PIC) was highly effective in controlling the disease under field conditions. Powdery scab incidence and severity on tubers were significantly reduced by MS applied at 219–222 L a.i. ha−1 by 66–98%. In application of PIC at 99–396 kg a.i. ha−1 followed with immediate plastic cover, disease incidence on tubers was significantly reduced by 56–90%, whereas, uncovered PIC treatments had a lower efficacy. Root galling was also affected by the fumigants and was significantly lower in MS and PIC treatments as compared to the control. In-furrow fluazinam treatments were less effective than the fumigants, with only 18–20% reduction in disease incidence on tubers. Pathogen levels in the soil, determined shortly after fumigation, were significantly lower than in the control. However, at the end of the growing season, they were increased to high levels with no significant differences among all treatments.

Predicting the slow decline of root lesion nematodes (Pratylenchus thornei) during host-free fallows to improve farm management decisions

Abstract Pratylenchus thornei is a major pathogen of cereal and legume crops around the world, especially in the northern grains region of eastern Australia. The dominance of host species within the rotation has seen soil pathogen population densities increase. Long weed-free fallows combined with sorghum production (non host crop) to reduce population densities has been successful. However, little is known about the rate of population decline during the fallow or how long this non–host period should continue in order to reduce the population below an accepted damage threshold. The rate of decline from a range of initial starting populations (high, medium, low and very low) were monitored over a 30 month weed free fallow. Fallows were initiated in November (late Spring) for three consecutive years. Nematode population densities and soil moisture were measured at eight depths down the soil profile to 1.5 m and used to describe the rate of population decline over time in each soil layer. Dynamic populations of P. thornei existed within the upper layers (

Growing for the future: Collective action, land stewardship and soilborne pathogens in California strawberry production

Outlook Growing for the future: Collective action, land stewardship and soilborne pathogens in California strawberry production Margaret Lloyd, UC Cooperative Extension Farm Advisor, Yolo, Solano and Sacramento counties Tom Gordon, Professor, Department of Plant Pathology, UC Davis Sustaining high strawberry yields will require an integrated approach that includes collaborative management of fields to limit the spread of soilborne pathogens. required, one that integrates advances in disease resistance through breeding with closer attention to the factors that influence the survival, activity and spread of pathogen populations in soil. Many of the latter, such as rotating crops and cleaning equipment, frequently involve multiple operators. As a result, there is a need to recognize that patho- gen-free soil is effectively a common-pool resource and that protecting it will require collective action. The end of methyl bromide Since the early 1950s, diseases caused by soilborne pathogens have been managed primarily through the use of preplant soil fumigation. Before that time, Verticillium wilt, caused by Verticillium dahliae, imposed a major limitation on strawberry production. Recognition of the fungicidal prop- erties of chloropicrin and the enhanced efficacy achieved by addition of methyl bromide lifted this http://calag.ucanr.edu • JULY–SEPTEMBER 2016 101 Jack Kelly Clark C alifornia accounts for more than 80% of U.S. strawberry production, a harvest worth $2.5 billion in 2014. Fertile soils and the prevail- ing climate on the Central Coast support per acre yields twice that of Florida, the second largest pro- ducer, and 10 times more than most other states. Yet California strawberry growers face sig- nificant challenges. Among the most important is the declining availability of suitable land. The potential for a given field to produce an acceptable yield depends not only on physical and chemical characteristics of the soil but also, critically, on the presence or absence of soil dwelling pathogens that can infect strawberry roots and cause diseases that limit fruit production. As described below, effec- tive control of soilborne pathogens of strawberries was once readily achieved by means that are no longer available to strawberry growers. It now seems likely that no single measure will suffice to meet the challenge of soilborne patho- gens. Rather, a multi-faceted approach will be

Evaluation of the biocontrol potential of Streptomyces goshikiensis YCXU against Fusarium oxysporum f. sp. niveum

A rhizobacterium with broad spectrum antifungal activity was isolated from the rhizosphere of a healthy cucumber plant in a Fusarium wilt diseased field. Phylogenetic tree analysis based on similarity percentage showed that the bacterium was 99% affiliated with the species Streptomyces goshikiensis. The strain, coded as S. goshikiensis YCXU, inhibited in vitro a broad range of phytopathogenic fungi, so it was selected for more detailed characterization. The strain could utilize different carbon sources and exhibited catalase, β-1,3-glucanase, chitinase and urease enzyme activities. The strain showed maximum growth at the pH of 7, temperature of 28°C and NaCl concentration of 1%. The stain was able to produce antifungal diffusible and volatile organic compounds that significantly inhibited the growth of pathogenic fungi. In the greenhouse experiments, watermelon plants fresh and dry weights were significantly increased, and the incidence of Fusarium wilt was decreased by 67% when the strain enriched by a bioorganic fertilizer was applied to both nursery soil and pot soil (NS). The treatment NS also showed 88.9% less pathogen population in soil as compared to control. The use of biocontrol agents decreased the stress indicator enzymes and malondialdehyde content by 55–70% and 62%, respectively as compared to control. The denaturing gradient gel electrophoresis (DGGE) analysis showed significant variations in the fungal and bacterial community structures of all treatments resulted from UPGMA cluster analysis. This study showed that S. goshikiensis YCXU could be a potential biocontrol agent for controlling watermelon Fusarium wilt disease.

Fate of Escherichia coli O157:H7 and Salmonella in soil and lettuce roots as affected by potential home gardening practices.

The survival and distribution of enteric pathogens in soil and lettuce systems were investigated in response to several practices (soil amendment supplementation and reduced watering) that could be applied by home gardeners. Leaf lettuce was grown in manure compost/top soil (0:5, 1:5 or 2:5 w/w) mixtures. Escherichia coli O157:H7 or Salmonella was applied at a low or high dose (10(3) or 10(6) colony-forming units (CFU) mL(-1) ) to the soil of seedlings and mid-age plants. Supplementation of top soil with compost did not affect pathogen survival in the soil or on root surfaces, suggesting that nutrients were not a limiting factor. Salmonella populations on root surfaces were 0.7-0.8 log CFU g(-1) lower for mid-age plants compared with seedlings. E. coli O157:H7 populations on root surfaces were 0.8 log CFU g(-1) lower for mid-age plants receiving 40 mL of water compared with plants receiving 75 mL of water on alternate days. Preharvest internalization of E. coli O157:H7 and Salmonella into lettuce roots was not observed at any time. Based on the environmental conditions and high pathogen populations in soil used in this study, internalization of Salmonella or E. coli O157:H7 into lettuce roots did not occur under practices that could be encountered by inexperienced home gardeners.

Assessment of compost for suppression of Fusarium oxysporum and improving Zea mays and Hibiscus sabdarriffa resistance to wilt diseases

The present research was conducted to evaluate the compost effectiveness on Zea mays and Hibiscus sabdarriffa under Fusarium wilt disease. Compost physical, chemical and biological characters were monitored weekly during the ripening process. Both coliform and nematode were tested. Finally, the effect of compost on pathogenicFusarium was examined within Z. mays and H. sabdarriffa in soil amended with 10% compost. Biochemical tests and antioxidant enzyme activities were determined for all the treated plants. The values of organic carbon recorded a percentage of 3.8%, while nitrogen (N), phosphorus (P) and potassium (K) values recorded 1.7, 4.6 and 5.6% higher than the commercial compost. The concentrations of nickel (Ni), copper (Cu), zinc (Zn), manganese (Mn), cobalt (Co), cadmium (Cd) and lead (Pb) in compost were below the threshold standard values. The compost is free of nematodes and coliform bacteria at maturity stage. Microbial population densities were usually high for Bacillus sp.compared to other microorganisms. In infected Z mays with compost, shoot height, fresh and dry weight increased significantly (62, 248 and 130%) and H. sabdarriffa also recorded increase in the same plant criteria. In infected Z. mays, a significant increase in catalase (CAT) and ascorbate peroxidase (APX) activities was recorded (162 and 150%). For H. sabdarriffa there was a significant decrease in APX activity (35%) with compost, while no significant differences in peroxidases (PODs) activity for both plants. In case of infection, a significant decrease was observed for both Z. mays and H.sabdarriffa compared to infected plants without compost. The observed disease suppression in compost-amended soil was associated with the reduction in soil pathogen population and increase in microbial activity of composts. Moreover, diversification of different organic materials in compost enhanced the activation of the microbial population in soil that eventually increases disease suppressiveness and effectively controlling Fusarium wilt. Key words: Antioxidant enzymes, compost, Hibiscus sabdarriffa, Zea mays.

Effect of Crop Rotation on the Soil Pathogen Population Dynamics and Canola Seedling Establishment

Effect of Crop Rotation on the Soil Pathogen Population Dynamics and Canola Seedling Establishment

Effects of Drip Irrigation on Population of Verticillium dahliae in Olive Orchards

AbstractVerticillium wilt of olive (Olea europaea L.), caused by Verticillium dahliae, is nowadays the most serious olive disease in Spain. The disease increments are being observed particularly in young olive plantations, favoured by several factors including inadequate cultural practices and crop production intensification, such as irrigation. Thus, three olive orchards affected by Verticillium wilt, with disease incidence ranging 30–50%, were selected to determine if the drip irrigation could favour the increase of pathogen in soil. Pathogen in soil was quantified in wet zones around the drippers and in dry zones out of them. Inoculum density in all experiments was higher in wet than in dry areas. After 4 months of watering, soil pathogen population increased considerably in wet and dry areas but inoculum density remained higher in the wet soil.

Factors Affecting Soybean Root Colonization by Calonectria ilicicola and Development of Red Crown Rot Following Delayed Planting.

Field studies were conducted in 1994, 1995, and 1996 to determine the effects of planting date, cultivar susceptibility, and soil pathogen population on soybean root colonization by Calonectria ilicicola and subsequent development of red crown rot. Early season colonization of roots was important for red crown rot symptom development. Symptom development in the more susceptible cultivar, Sharkey, was reduced following delayed planting and remained low in the less susceptible cultivar, Cajun, regardless of planting date. Taproot colonization was positively correlated with inoculum density during all three growing seasons but was strongest in 1994. Also, lateral root colonization correlated positively with inoculum density in 1994, the only year in which foliar symptoms were detected. A substantial decrease in inoculum density in 1995, along with reduced soybean root colonization, were attributed to high soil temperatures and probably low rainfall recorded during that summer. The effect of soybean plant age on root colonization was examined by exposing plants to the pathogen at different ages. Soybean plants were most susceptible to C. ilicicola during the first week after seedling emergence. By the second week, susceptibility was reduced by nearly half, and it remained near that level for the next several weeks.

Application of Preplant Fumigants via Drip Irrigation Systems for the Management of Root Rot of Melons Caused by Monosporascus cannonballus.

Root rot and vine decline, caused by Monosporascus cannonballus, is a destructive disease of melons in the desert production regions of southern California. In 1998, we initiated studies on the use of preplant fumigation to reduce resident pathogen populations in soil. Preplant fumigation with methyl iodide injected as a hot gas at 448.4 kg/ha through drip irrigation tape in preformed, tarped beds consistently provided significant (P < 0.05) reductions in the percentage of roots infected compared with the nonfumigated controls; these reductions were equal to or better than those achieved with an equivalent rate (448.4 kg/ha) of methyl bromide. Chloropicrin applied in water at 249.0 kg/ha through buried drip irrigation tape to either tarped or nontarped beds significantly (P < 0.05) reduced the percentages of both roots infected and roots on which perithecia were produced compared with nonfumigated controls.

우리나라 배추 뿌리혹병 연구 현홍과 향후과제

Clubroot disease of curcifer crops caused by Plasmodiophora brassicae had been first reported in 1928 in Korea, and maintained mild occurrence until 1980s. Since 1990s the disease has become severe in alpine areas of Kyonggi and Kangwon, gradually spread to plain fields throughout the country, and remains as the great-est limiting factor for its production. Researches on the disease has begun in late 1990s after experiencing severe epidemics. Survey of occurrence and etiological studies have been carried out, particularly, on the pathogen physiology, race identification, quantification of soil pathogen population, and host spectrum of the pathogen. Ecology of gall formation and its decay, yield loss assessment associated with time of infection, and relationships between crop rotation and the disease incidence was also studied during late 1990s. In studies of its control, more than 200 crucifer cultivars were evaluated for their resistance to the disease. Lime applica-tion to field soil was also attempted to reduce the disease incidence. Resistant radish and welsh onion were recommended as rotation crops with crucifers after 3-year field experiments. However, so for, most studies on clubroot disease in Korea have been focused on chemical control. Two fungicides, fluazinam and flusulfamide, were selected and extensively studied on their application technologies and combination effects with lime application or other soil treatment. To develop environmentally-friendly control methods, solar-disinfection of soil, phosphoric acid as a nontoxic compound, and root-parasiting endophytes as biocontrol agents were examined for their effects on the disease in fields. In the future, more researches are needed to be done on development of resistant varieties effective to several races of the pathogen, establishment of economically-sound crop rotation system, and improvement of soil-disinfection technique applicable to Korean field condi-tion, and development of methodology of pretreatment of fungicides onto seeds and seedbeds.

Detection and quantification of fungal and bacterial potato pathogens in plants and soil*

We have developed polymerase chain reaction (PCR)‐based diagnostic assays for fungal and bacterial diseases of potato together with rapid methods of DNA extraction and purification from soil and plant samples. Pathogen detection and quantification is a crucial step in the control of crop diseases. PCR primers were designed to unique sequences for specific detection of the potato blemish complex of pathogens: Spongospora subterranea (powdery scab), Streptomyces scabies (common scab), Helminthosporium solani (silver scurf), Rhizoctonia solani AG‐3 (black scurf) and Colletotrichum coccodes (black dot). A multiplex PCR test was designed with a high level of sensitivity to detect H. solani, C. coccodes, and S. scabies simultaneously in one reaction, and individual quantitative PCR assays were also developed to detect these pathogens and S. subterranea in soil and tubers. PCR‐based detection systems for the major storage‐rot pathogens of potato (Fusarium spp., Phoma foveata, Pythium ultimum and Phytophthora erythroseptica) are also under development. The potential of these techniques to detect and monitor these pathogen populations in soil and potato tubers for epidemiological studies is discussed.

Formulations ofFusarium oxysporumf.sp.erythroxylifor biocontrol ofErythroxylum cocavar.coca

Formulations ofFusarium oxysporumSchlechtend:Fr. f.sp.erythroxyliisolate EN-4, pathogenic toErythroxylum cocavar.coca(coca) were evaluated in greenhouse and field studies to determine their relative ability to enhance pathogen populations in the soil or cause disease in coca. The formulations rice-alginate prill, Pesta, and C6 were most thoroughly tested and are products of three formulation processes. The formulations were applied in the greenhouse and field at 33.6 kg ha−1. All the formulations tested enhanced the population of EN-4 in the soil during greenhouse (&gt; 6 wk) and field (&gt; 7 mo) experiments. EN-4 was present in the upper 1 cm of formulation-treated soil at &gt; 200-fold higher populations than established below a depth of 7 to 10 cm in both greenhouse and field experiments. This population distribution was maintained throughout the 7-mo sampling period for field experiments. The enhanced soil populations of EN-4 were associated with an increase in root colonization by the pathogen EN-4 in the field 5 to 7 mo after treatment. The formulatedF. oxysporumbegan to have a significant effect on plant death 100 to 200 d after application in two of three field experiments, based on repeated measures analysis. The various formulations tested tended to establish similar pathogen populations in soil and subsequently caused similar levels of disease. The primary factors influencing formulation performance may be environmental, since inoculum production is dependent on sporulation of the formulation, which, although rapid, may continue over several weeks subsequent to application.

AUTOLOGISTIC MODEL OF SPATIAL PATTERN OF PHYTOPHTHORA EPIDEMIC IN BELL PEPPER: EFFECTS OF SOIL VARIABLES ON DISEASE PRESENCE

The pathogen Phytophthora capsici causes lesions on the crown, stem, and leaves of bell pepper, and rapidly causes the plant to die. The spatial patterns of disease in an agricultural field contain information about pathogen dispersal mechanisms and can be useful for developing methods of control of disease. Soil water content, soil pathogen population density, and disease incidence data were collected on a 20 x 20 grid in two naturally infested commercial bell pepper fields. In one field the initial pattern of disease closely matched the soil water content pattern and disease developed in areas where the pathogen population levels were high. In the other field no such correspondence was obvious from maps of disease and soil water content . The auto logistic model is a flexible model for predicting presence or absence of disease based on soil water content and soil pathogen population, while taking spatial correlation into account. In the autologistic model the log odds of disease in a particular quadrat are modeled as a linear combination of disease in neighboring quadrats and the soil variables. Neighboring quadrats can be defined as adjacent quadrats within a row, quadrats in adjacent rows, quadrats two rows away, and so forth. The regression coefficients give estimates of the increase in odds of disease if neighbors within a row or in adjacent rows show disease symptoms; thus we obtain information about the degree of spread in different directions. The coefficients for the soil variables give estimates of the increase in odds of disease as soil water content or pathogen population density increase. In this problem, soil water content is also highly correlated over quadrats. This introduces a kind of collinearity between water content and the disease in neighboring quadrats, making estimation and interpretation of the parameters of the auto logistic model more difficult. We discuss fitting and evaluating the autologistic model when the covariates are themselves spatially correlated .

Utilization of waste materials in nematode control: A review

The addition of waste materials from animals and plants to soil has been explored as an alternative means of nematode control. These materials include agricultural wastes in the form of green manures and dried-crop residues in general and industrial by-products, such as oilcakes, sawdust, cellulosic waste, and sugar-cane bagasse in particular. Besides these, other biological wastes (chitin, bone meal, horn meal, sewage-sludge, municipal refuse, and livestock wastes) have been proved succesful in controlling nematodes for several years. The beneficial effects of organic incorporation have been generally considered to be due to direct or indirect stimulation of predators and parasites of plant-parasitic nematodes. Very often, when there was a decrease in the soil-pathogen population, there was a consequent increase in crop yield. This review reveals a promising area of ‘non-conventional’ nematode-management.

The Direct Assay of Plant Pathogen Populations in Soil

The Direct Assay of Plant Pathogen Populations in Soil