Screening of common bean (Phaseolus vulgaris) for resistance against temperate root-knot nematodes (Meloidogyne spp.)

BACKGROUND: An important part of the production area of common bean (Phaseolus vulgaris L.) in Belgium is located on the sandy soils of the provinces of Antwerp and Limburg where Meloidogyne chitwoodi (Golden), M. fallax (Karssen) and M. hapla (Chitwood) are present. The host plant status of ten bean cultivars for root‐knot nematodes was determined by evaluating penetration, development and egg mass formation after inoculation with second‐stage juveniles. RESULTS: The tested cultivars were poor to good hosts for M. chitwoodi, non‐hosts or bad hosts for M. fallax and excellent hosts for M. hapla. Significantly fewer M. fallax were found in the roots, and their development was delayed. Penetration of M. hapla took place over a longer period than that of M. chitwoodi and M. fallax. The number of mature females of M. chitwoodi in cv. Polder 6 weeks after inoculation was no different from that in other cultivars, although fewer egg masses were found on this cultivar in the screening test. There was no influence of M. chitwoodi on vegetative growth of cv. Polder. CONCLUSION: The differences found in host plant status of bean cultivars stress the importance of a correct diagnosis of the Meloidogyne species in agricultural fields. Cultivar Polder showed potential as a trap crop for M. chitwoodi. Copyright © 2011 Society of Chemical Industry     

旱地燕麦间作对土壤酶活性、微生物含量及产量的影响

本文通过研究内蒙古旱作区禾本科、豆科及茄科间作对土壤生物性状的影响，旨在揭示燕麦（Avena sativa Linn）与不同作物间作及其单作在土壤酶活性、微生物量及土地当量比（LER）等方面的优势机理。本试验设置燕麦、黑豆（Glycinemax（L.）merr）、苜蓿（Medicago sativa）、马铃薯（Solanum tuberosum L）单作和黑豆间作燕麦、苜蓿间作燕麦、马铃薯间作燕麦共7个处理，探讨各处理对上述各指标的影响。结果表明：燕麦间作黑豆土地当量比最高，2015年和2016年分别为1.62和1.65。燕麦间作黑豆土壤脲酶活性和蔗糖酶活性较苜蓿间作燕麦、马铃薯间作燕麦显著提高了5.00%~51.61%和5.73%~52.29%。2015年和2016年播种后75 d苜蓿间作燕麦土壤过氧化氢酶活性显著高于黑豆间作燕麦，分别提高了29.47%和40.56%。黑豆间作燕麦对比其他两间作处理土壤微生物的生物量碳、氮含量分别显著提高了2.70%~17.89%和11.36%~26.47%，土壤脲酶活性提高了1.51%~55.22%，蔗糖酶活性提高了5.73%~52.29%，是该地区最优的间作模式。     

Vertical Distribution of the Plant-Parasitic Nematode, Pratylenchus penetrans, Under Four Field Crops

ABSTRACT The vertical distribution of Pratylenchus penetrans was monitored in four fields cropped with maize, black salsify, carrot, or potato. Soil samples were collected at 21-day intervals from May 2002 until April 2003 from five plots (2 x 5 m(2)) per field. Per plot, 15 cores were taken to a depth of 70 cm and split into seven segments of 10 cm each. Within the plots, segments from corresponding depths were pooled. After mixing, 200-g subsamples were taken and nematodes were extracted by zonal centrifugation from the root fraction and the mineral soil fraction separately. In most crops, the root fraction contained more than 50% of the total number of P. penetrans. Because the ratio between the numbers of nematodes in the root fraction and mineral soil fraction changes during the growing season, numbers of P. penetrans found in the mineral soil fraction cannot be used to estimate the total number in the soil. Therefore, both fractions have to be processed to obtain a reliable estimate of the density. No nematodes were recovered below 50 cm soil depth, except in the maize field where nematodes were found at 70 cm. The optimum sampling depth for maize, black salsify, carrot, and potato was 45, 25, 25, and 35 cm, respectively. The percentage of nematodes per soil layer was independent of the sampling date, indicating that a defined optimum sampling depth will be applicable throughout all seasons. The cumulative vertical distribution, modeled with a logistic equation, can be used to estimate the sampling error when samples are collected at different depths.     

Effect of crop rotation on the incidence of soil-borne fungal diseases of potato

Effects of crop rotation on the incidence of soil-borne pathogens and on the performance of potato were investigated in five field experiments. Rotations differed in cropping frequency of potato and in crop sequence.Incidence of stem canker caused byRhizoctonia solani was strongly influenced by the cropping frequency of potato and not by crops with which the potato was alternated in the rotation. Cropping frequency of potato also affected the occurrence of black scurf, but less pronounced than for stem canker. The antagonistVerticillium bigutatum slightly reducedR. solani (black scurf) in plots on sandy soil continuously cropped with potato. Incidence of stem canker was also strongly affected by granular nematicides applied to the soil, nitrogen level and the cultivar grown.     

Meloidogyne chitwoodi and Meloidogyne fallax in France: initial management experiences

Since 2008, the French NPPO has been controlling two outbreaks of Meloidogyne chitwoodi and Meloidogyne fallax, in Picardie (open fields) and in Bretagne (glasshouses). Intensive investigations have been undertaken to delimit these outbreaks and to help formulate the best control management strategy to adopt in these two very different situations. In open fields, eradication measures have been implemented, with bare fallow in infested fields being adopted as the main measure, despite the impact on affected growers and high financial cost. Recently, soil analyses in fields after 2 years of bare fallow showed that neither M. chitwoodi nor M. fallax was detected in 99% of cases, and measures have now been reduced: crops such as cereals are now allowed in these fields, but no tubers or root crops can be grown. Under glasshouses, eradication was not considered feasible and so a containment strategy was followed. An extensive national survey of susceptible crops has also been carried out for early detection of possible new outbreaks.     

Effect of plant roots on the germination of microsclerotia ofVerticillium dahliae

Induction of germination of microsclerotia by exudates from plant roots may be important for the control ofV. dahliae. Laboratory experiments with root observation boxes were carried out to assess the influence of root tips of seven crop species and cultivars on the germination of microsclerotia ofVerticillium dahliae in soil under controlled conditions. The root density of crops was measured in a field experiment. The results of the laboratory experiments and the field experiment were combined to estimate the total effect of crops on the population of microsclerotia in the field. Germination of microsclerotia was stimulated by all crops compared to a control without a crop. Among crops, roots of potato cvs Element and Astarte had a larger stimulation effect on microsclerotia than that of potato Ostara, pea, flax, sugar beet or onion. The number of hyphae per microsclerotium decreased with distance from the root surface regardless of the crop species or cultivar. Differences in root densities, in the affected root zones and in the stimulation effect on germination of microsclerotia caused large differences among crops in the effect on the population of microsclerotia in the soil. However, growing a rop with the special purpose to reduce the level ofV. dahliae inoculum in the soil is an inefficient control measure, because only a small part of the total soil volume is affected by roots and the number of hyphae per microscleroium affected is too low.Abbreviations MS microsclerotia, microsclerotium     

The effect of post‐harvest storage conditions on the development of black dot (Colletotrichum coccodes) on potato in crops grown for different durations

The effects of post‐harvest curing and storage temperature on severity of black dot, caused by Colletotrichum coccodes, were investigated for potato crops grown for different crop durations (days from 50% emergence to harvest) in soils that posed a low, medium and high risk of disease. In field trials over four growing seasons (2005–8), black dot severity at harvest increased with increasing crop duration, within the range 103–146 days from 50% emergence to harvest (P < 0.05). In field trials over three growing seasons (2006–8), black dot severity on tubers at harvest increased significantly with increasing soil inoculum in each year, within the range 43–4787 pg C. coccodes DNA/g soil (P < 0.05). Storage trials were conducted to measure the influence of accumulated post‐harvest temperature on black dot. In 2005, no difference in black dot severity was observed on tubers stored for 20 weeks at 2.5 and 3.5 °C. In 2006 (but not 2007), increasing the duration of curing after harvest from 4 to 14 days increased black dot severity on tubers from 8.9 to 11.2% (P < 0.01) in long duration crops (>131 days after 50% emergence) grown under high (>1000 pg C. coccodes DNA/g soil) soil inoculum. The number of days of curing did not affect disease severity for shorter duration crops grown at high soil inoculum, or on crops grown at medium or low (100–1000 and <100 pg C. coccodes DNA/g soil, respectively) soil inoculum concentrations. Soil inoculum and crop duration together provided a reasonable prediction of black dot severity at harvest and after a 20‐week storage period.     

Spread of levan-positive populations of <Emphasis Type="Italic">Pseudomonas savastanoi</Emphasis> pv. <Emphasis Type="Italic">savastanoi</Emphasis>, the causal agent of olive knot,in central Italy

Mixtures of wet vegetable wastes (Brassica, carrot or onion) and dry onion waste were composted at 50 °C for 7 days. The incorporation of the raw or composted vegetable waste mixtures into sandy loam, silt and peat soils reduced the viability of sclerotia of S. cepivorum in glasshouse pot bioassays. The reduction in viability was dependent on waste type, rate of incorporation, duration of exposure and soil type. Onion waste was the most effective waste type in reducing sclerotia viability in all three soils. The Brassica and carrot wastes were as effective as the onion waste in silt soil but less effective in sandy loam and peat soil. A 50% w/w incorporation rate of the wastes gave the largest reduction in viability, with an increase in reduction over time. Composted onion waste reduced sclerotia viability under glasshouse and field conditions although the effect was smaller in the field. Composted onion waste incorporated into soil at 50% w/w reduced the incidence of Allium white rot on onion seedlings in glasshouse pot tests. Incidence and control of the disease differed with soil type. The most consistent control was achieved in peat soil whereas no control was observed in silt soil. Incorporation of the waste 2 months prior to sowing or transplanting reduced seedling emergence in sandy loam soil and growth in all three soil types. The potential for field application of composted vegetable wastes as a sustainable method for control of Allium white rot and waste disposal is discussed.     

Fusarium oxysporum f.sp. cepae dynamics: in-plant multiplication and crop sequence simulations

To reduce Fusarium Basal Rot caused by Fusarium oxysporum f.sp. cepae (Foc) through crop rotation, plant species should be selected based on Foc multiplication in their roots. Foc multiplication rates in 13 plant species were tested in a greenhouse. All plant species enabled Foc multiplication. The lowest Foc levels (cfu g^?1 dry root) were found for wheat, sunflower, cowpea and millet, the highest for black bean. The highest Foc levels per plant were calculated for sudan grass. These data were used to calibrate the model Pf?=?Pi/(α?+?βPi) relating final (Pf) and initial (Pi) Foc levels in the soil. The rate of population increase at low Pi (1/α) was highest for onion and black oat and smallest for sunflower. The pathogen carrying capacity (1/β) was highest for black oat and black bean, and lowest for wheat, cowpea and foxtail millet. Foc soil population dynamics was simulated for crop sequences by concatenating Pi-Pf values, considering instantaneous or gradual pathogen release after harvest. Different soil Foc populations were attained after reaching steady states. Foc populations in the sequence onion –foxtail millet - wheat – cowpea were 67 % lower than in the sequence onion – sudan grass - black oat - black beans. In this work, by combining detailed greenhouse experiments with modelling, we were able to screen crops for their ability to increase Foc population and to explore potential crop sequences that may limit pathogen build-up.     

Seasonal activity of EPTC for Cyperus rotundus L. control in a tropical climate*

Four experiments were conducted at six week intervals to determine the seasonal activity and persistence of soil-incorporated EPTC (5-ethyl N,N-dipropyl(thiocarbamate)) for Cyperus rotundus L. control and tolerance of okra (Hibiscus esculentus L.), cucumber (Cucumis sativus L.), lettuce (Lactuca sativa L.), red beet (Beta vulgaris L.) and carrot (Daucus carota L.) during the dry and wet seasons in Viçosa, Brazil. Satisfactory control of C. rotundus was obtained at 2 kg/ha EPTC during the dry season and 4 kg/ha or more during the wet season. Only red beet and carrot tolerated these doses of EPTC when the crops were planted five days after application. However, selective control of C. rotundus was obtained when the planting date of lettuce was delayed for three or six weeks after EPTC application. EPTC controlled C. rotundus at half the dose that was required to control three species of annual grass that germinated near the soil surface. EPTC persisted longer when applied to air dry soil and incorporated with a rototiller than when incorporated into moist or wet soil.     

Survival of pathogens of Brussels sprouts (Brassica oleracea Gemmifera Group) in crop residues

Mycosphaerella brassicicola (ringspot), Alternaria brassicicola and A. brassicae (dark leaf spot) and Xanthomonas campestris pv. campestris (black spot) can infect leaves of Brussels sprouts resulting in yield losses. Infections of outer leaves of sprouts cause severe losses in quality. Crop residues can be a major primary inoculum source of the pathogens. Their population dynamics were followed in residues of leaves and stalks of crops of Brussels sprouts during 24 months using real‐time PCR assays. Leaf residues on the soil surface or buried in soil decomposed within 4 months. However, residues of stalks were present in the field after 24 months. In such residues, M. brassicicola populations increased during the first 2 months, but decreased thereafter and the pathogen was found only occasionally in the second year. Alternaria brassicicola multiplied on stalks exposed on the surface of field soil and was present on such residues after 24 months. Survival was less on residues buried in soil. Alternaria brassicae population increased in stalks exposed on the soil surface during the first months but decreased thereafter under the detection limit. Xanthomonas campestris cv. campestris populations fluctuated in time but 1 × 10⁴ cells mg^?1 stalk residue were still found after 24 months. Additionally, the four pathogens were present in residues of 11 commercial rapeseed crops that were analysed. The observed variation in population sizes of the pathogens between individual pieces of crop residues indicates a stochastic spread of pathogens. Unravelling the underlying processes will support the development of novel methods for sustainable disease prevention.     

Prognose-Modell zur Erfassung des Rückstandsverhaltens von Metribuzin und Methabenzthiazuron im Boden und deren Auswirkungen auf Folgekulturen

A predictive model for the assessment of metribuzin and methabenzthiazuron residues in soil and their effects on succeeding crops Aus der simulierten Abbaukurve lassen sich somit für jeden beliebigen Zeitraum nach Applikation eines Herbizids die maximalen pflanzenverfügbaren Wirkstoffanteile ableiten, aus denen die Auswirkungen auf mögliche Folgekulturen prognostiziert wurden. Die relative Empfindlichkeit (im Bereich der ED₅₀) der untersuchten Kulturpflanzen in Hydroponik war bei Metribuzin: Möhre < Bohne = Salat < Erbse = Spinat und bei MBT: Bohne = Erbse = Salat < Spinat = Möhre. Weiterhin konnte gezeigt werden, dass unter Labor- und Freilandbedingungen evtl. auftretende Schäden in fast allen Fällen in den gleichen Aktivitäskategorien lagen. The degradation of the herbicides metribuzin and methabenzthiazuron (MBT) was simulated under outdoor conditions in a sandy soil by a computer model based on the dominating influence of temperature and moisture on degradation, which is measured in preceding laboratory experiments. Depending on the conditions of incubation (10–30°C, 20–90% water holding capacity) the half-life of metribuzin was 11–60 days and of MBT 42 > 1200 days. Knowing the plant available soil water, the fraction of a total herbicide residue potentially available to plants can be calculated from the distribution coefficient (K_d-value). In the soil under investigation, for metribuzin 77% and for MBT 16% of the total residue was available to plants. Thus, the maximum residue available to plants can be calculated from the simulated degradation curve for any period after the application of a herbicide and in combination with a predictive model the effect on succeeding crops can be predicted. The specific susceptibility of the crops in question has to be established in preceding hydroponic culture experiments. The relative susceptibility (about ED₅₀) of the plants in hydroponic-culture was earrot相似文献   

Seasonal dynamics of the pink root fungus (Setophoma terrestris) in rhizosphere soil: Effect of crop species and rotation

Setophoma terrestris, a ubiquitous inhabitant of soil, causes pink root rot in various crops. In the present study, the density of S. terrestris was estimated by quantitative real-time PCR in onion and non-onion fields of Hokkaido, the northernmost island of Japan. Three-year observations in monoculture and rotation fields demonstrated that the fungus grew significantly from the third year onwards, and declined in fields planted with poor hosts (e.g., sugar beet and soybean) that produced few or no chlamydospores of S. terrestris. Seasonal analysis revealed that the population of S. terrestris consistently increased when the tops of onions fell over in summer, which is when root activity declines. However, the soil inoculum potential estimated by a seedling bioassay showed distinct seasonal patterns, which rose from post-harvest in winter and remained high until the subsequent planting in spring. Detailed surveys on depth distribution in an onion field detected a high population of S. terrestris in the effective layer (10–30 cm deep) but not below the hardpan (40 cm), implying that the fungus is intimately associated with roots. These results indicate that the proliferation of the fungus is closely related to root senescence and that over-wintered propagules play an important role in primary infections, affecting disease severity. The present study shows that the temporal dynamics of S. terrestris depend exclusively on the activity of infecting roots and provides circumstantial evidence on the deleterious impact of monoculture on crop production.     

Seed dormancy,germination, emergence and seed longevity in Galinsoga parviflora and G. quadriradiata

Galinsoga quadriradiata (hairy galinsoga) and Galinsoga parviflora (smallflower galinsoga, gallant soldier) are very troublesome weeds in many vegetable row crops in Europe. To optimise management strategies for Galinsoga spp. control, an in‐depth study of germination biology was performed. Germination experiments were conducted to evaluate the impact of light and alternating temperatures on germination of a large set of Galinsoga populations. Seedling emergence was investigated by burying seeds at different depths in a sandy and sandy loam soil. Dormancy of fresh seeds harvested in autumn was evaluated by studying germination response in light at 25/20°C with and without nitrate addition. Seed longevity was investigated in an accelerated ageing experiment by exposing seeds to 45°C and 100% relative humidity. Galinsoga spp. seeds required light for germination; light dependency varied among populations. Seedling emergence decreased drastically with increasing burial depth. Maximum depth of emergence varied between 4 and 10 mm depending on soil type and population. In a sandy soil, emergence percentages were higher and seedlings were able to emerge from greater depths than in a sandy loam soil. Freshly produced G. parviflora seeds, harvested in autumn, showed a varying but high degree of primary dormancy and were less persistent than G. quadriradiata seeds that lack primary dormancy. Lack of primary dormancy of freshly harvested G. quadriradiata seeds and light dependency for germination may be used to optimise and develop Galinsoga management strategies.     

Inoculum potential of Sclerotinia sclerotiorum sclerotia depends on isolate and host plant

The soilborne fungus Sclerotinia sclerotiorum infects many important crop plants. Central to the success of this pathogen is the production of sclerotia, which enables survival in soil and constitutes the primary inoculum. This study aimed to determine how crop plant type and S. sclerotiorum isolate impact sclerotial production and germination and hence inoculum potential. Three S. sclerotiorum isolates (L6, L17, L44) were used to inoculate plants of bean, carrot, lettuce, oilseed rape (OSR) and potato, and the number and weight of sclerotia per plant quantified. Carpogenic germination of sclerotia collected from different hosts was also assessed for L6. Production of sclerotia was dependent on both crop plant type and S. sclerotiorum isolate, with OSR and lettuce supporting the greatest number (42–122) and weight (1.6–3.0 g) of sclerotia per plant. The largest sclerotia were produced on OSR (33–66 mg). The three S. sclerotiorum isolates exhibited a consistent pattern of sclerotial production irrespective of crop type; L6 produced large numbers of small sclerotia while L44 produced smaller numbers of large sclerotia, with L17 intermediate between the two. Germination rate and percentage was greatest for larger sclerotia (4.0–6.7 mm) and also varied between host plants. Combining sclerotial production data and typical field crop densities suggested that infected carrot and OSR could produce the greatest number (3944 m^?2) and weight (73 g m^?2) of S. sclerotiorum sclerotia, respectively, suggesting these crops potentially contribute a greater increase in inoculum. This information, once further validated in field trials, could be used to inform future crop rotation decisions.     

Apera spica-venti population dynamics and impact on crop yield as affected by tillage, crop rotation, location and herbicide programmes

Apera spica‐venti is a winter annual grass and, increasingly, a severe weed problem in autumn‐sown crops. Non‐inversion tillage has become more common in Denmark in recent years, but may accentuate problems with A. spica‐venti. These problems may be avoided, if selected preventive and cultural weed management practices are adopted. To this end, we conducted a 4‐year field study investigating the effects of crop rotation, tillage method, location and limited herbicide input on A. spica‐venti population dynamics and crop yield. Additionally, detailed studies were performed on the fate of A. spica‐venti seeds when incorporated to different soil depths. The location with a lighter soil texture, cooler climate and higher rainfall favoured A. spica‐venti growth and consequently crop yield loss, especially in the crop sequence comprised only of autumn‐sown crops and with non‐inversion tine tillage. Incorporating A. spica‐venti seeds in the soil improved their survival, explaining the higher A. spica‐venti proliferation seen with tine tillage as opposed to direct drilling. The rotations including an even mixture of spring‐ and autumn‐sown crops did not lead to noteworthy changes in the A. spica‐venti population, irrespective of tillage method. Thus, in many regions, management of A. spica‐venti will require rotations that balance autumn‐ and spring‐sown crops.     

Soil metabolism of the herbicide napropamide in cereals, maize, sugar beet and vegetable field replacement crops

The metabolism of the herbicide napropamide has been studied in the field in the soil of replacement crops (cereals, corn, sugar beet, potato and several vegetables). Napropamide was soil applied in the autumn and the soil left fallow during the winter. Crops were sown in April of the following year and simulated the replacement crops that are grown in the event of failure of the first autumn-sown crop. Trials were made twice, i.e. during the 1987-1988 and 1988-1989 crop seasons. The soil metabolism of napropamide was also studied in a rose nursery. Napropamide was transformed by microbiological processes in the soil into the corresponding monoethylamide and acid. These compounds did not generally accumulate in the soil, and their individual concentrations did not exceed that of residual napropamide during the observed growing seasons. The kinetics, metabolic pathways and agricultural implications of the herbicide are briefly discussed.     

Alternative hosts of <Emphasis Type="Italic">Curtobacterium flaccumfaciens</Emphasis> pv. <Emphasis Type="Italic">flaccumfaciens</Emphasis>, causal agent of bean bacterial wilt

Alternative hosts are an important way of phytopathogenic bacteria survival between crop seasons, constituting a source of inoculum for the following crops. Bacterial wilt, caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), is one of the most important diseases for common bean, and little information is available about the host range of the bacterium. In this study, we assessed possible alternative hosts for Cff, especially those cultivated during winter, in rotation systems with common bean. Plants of barley, black oat, canola, radish, ryegrass, wheat and white oat, were assessed under field and greenhouse conditions. Cff colonized epiphytically all plant species and endophytically black oat, ryegrass, wheat and white oat plants assessed in the greenhouse assays. Under field conditions, Cff colonized all plant species by except radish. All bacterial strains re-isolated from the plants were pathogenic to common bean and identified as Cff by PCR with specific primers. Based on our results, the cultivation of bean crop in succession with barley, black oat, canola, ryegrass, wheat and white oat should not be recommended, mainly in areas with a history of bacterial wilt occurrence. In these cases, the better option for crop rotation during the winter is radish, a non-alternative host for Cff.     

Effects of crop rotation and removal of crop debris on the soil population of two isolates of Verticillium dahliae

Microsclerotia of Verticillium dahliae are produced in large numbers on senescing parts of host plants and remain viable in the soil for many years. Changes in the population density, i.e. density of microsclerotia, in the soil were measured in micro-plots using two isolates of V. dahtiae , specific to either field bean or potato, several crop sequences comprising potato, field beans and barley, and either the removal of aerial debris of the crops or incorporation into soil.
Potato was more susceptible to the potato isolate and field bean more susceptible to the field bean isolate. Removal of debris of potato and field bean reduced numbers of microsclerotia in the soil in the subsequent years, but removal of barley straw had no effect. Initially non-infested control micro-plots became infested, probably by the growth of potato roots into the naturally infested subsoil. The rate of increase of the microsclerotial population in the non-infested control micro-plots was larger than in the initially infested treatments, because more colonized debris was produced. It is concluded that removal of aerial debris of host crops is important to reduce the soil population of V. dahtiae.     

Long-Term Biosanitation by Application of Coniothyrium minitans on Sclerotinia sclerotiorum-Infected Crops

ABSTRACT The effect of the fungal mycoparasite Coniothyrium minitans applied as a spray to crops infected with Sclerotinia sclerotiorum (causal agent of white mold) on contamination of soil with S. sclerotiorum sclerotia was studied in a 5-year field experiment. Sclerotial survival also was monitored during two subsequent years, when the field was returned to commercial agriculture. In a randomized block design, factorial combinations of four crops and three treatments were repeated 10 times. Potato (Solanum tuberosum), bean (Phaseolus vulgaris), carrot (Daucus carota), and chicory (Cichorium intybus), which are all susceptible to S. sclerotiorum, were grown in rotation. Plots were treated with C. minitans or Trichoderma spp. or were nontreated (control). Crops were rotated in each plot, but treatments were applied to the same plot every year. After 3 years during which it showed no effect on sclerotial survival, the Trichoderma spp. treatment was replaced by a single spray with C. minitans during the fourth and fifth years of the trial. The effect of treatments was monitored in subsequent seasons by counting apothecia as a measure of surviving S. sclerotiorum sclerotia and scoring disease incidence. Trichoderma spp. did not suppress S. sclerotiorum, but C. minitans infected at least 90% of S. sclerotiorum sclerotia on treated crops by the end of the each season. C. minitans lowered the number of apothecia compared with the other treatments during the second year after the bean crop. C. minitans reduced the number of apothecia by approximately 90% when compared with the control and Trichoderma spp. treatments and reduced disease incidence in the bean crop by 50% during the fifth year of the trial, resulting in a slightly higher yield. In 1993, but not 1994, a single spray with C. minitans was nearly as effective at reducing apothecia as three sprays (monitored in 1995). The final population size of sclerotia in soil at the end of the 7-year period was lower in all C. minitans plots than at the beginning of the trial, even in plots where two highly susceptible bean crops were grown during the period. The results indicate that the mycoparasite C. minitans has the potential to keep contamination of soil with sclerotia low in crop rotations with a high number of crops susceptible to S. sclerotiorum.