Analyses of Lettuce Drop Incidence and Population Structure of Sclerotinia sclerotiorum and S. minor

ABSTRACT To understand the geographical distribution of lettuce drop incidence and the structure of Sclerotinia minor and S. sclerotiorum populations, commercial lettuce fields were surveyed in the Salinas, San Joaquin, and Santa Maria Valleys in California. Lettuce drop incidence, pathogen species, and mycelial compatibility groups (MCGs) were determined and analyzed using geostatistic and geographical information system tools. Lettuce drop incidence was lowest in the San Joaquin Valley, and not significantly different between the other two valleys. Semivariogram analysis revealed that lettuce drop incidence was not spatially correlated between different fields in the Salinas Valley, suggesting negligible field-to-field spread or influence of inoculum in one field on other fields. Lettuce drop incidence was significantly lower in fields with a surface drip system than in fields with furrow or sprinkler irrigation systems, suggesting that the surface drip system can be a potential management measure for reducing lettuce drop. In the San Joaquin Valley, S. sclerotiorum was the prevalent species, causing drop in 63.5% of the fields, whereas S. minor also was identified in 25.4% of the fields. In contrast, in the Salinas Valley, S. minor was the dominant species (76.1%) whereas S sclerotiorum only observed in only 13.6% fields, in which only a few plants were infected by S. sclerotiorum. In the Santa Maria Valley, both species frequently were identified, with S. minor being slightly more common. Although many MCGs were identified in S. minor, most of them consisted of only one or two isolates. In all, approximately 91.4% of the isolates belonged to four MCGs. Among them, MCG-1 was the most prevalent group in all three valleys, accounting for 49.8% of total isolates. It was distributed all over the surveyed areas, whereas other MCGs were distributed more or less locally. Populations of S. sclerotiorum exhibited greater diversity, with 89 isolates collected from the Salinas and San Joaquin Valleys belonging to 37 different MCGs. Among them, the most recurrent MCG-A contained 16 isolates, and 30 MCGs contained only 1 isolate each. Many MCGs occurred within only one or a part of the two valleys. Potential reasons for this abundant diversity are discussed.     

Germination of Sclerotinia minor and S. sclerotiorum Sclerotia Under Various Soil Moisture and Temperature Combinations

ABSTRACT Sclerotial germination of three isolates each of Sclerotinia minor and S. sclerotiorum was compared under various soil moisture and temperature combinations in soils from Huron and Salinas, CA. Sclerotia from each isolate in soil disks equilibrated at 0, -0.03, -0.07, -0.1, -0.15, and -0.3 MPa were transferred into petri plates and incubated at 5, 10, 15, 20, 25, and 30 degrees C. Types and levels of germination in the two species were recorded. Petri plates in which apothecia were observed were transferred into a growth chamber at 15 degrees C with a 12-h light-dark regime. All retrievable sclerotia were recovered 3 months later and tested for viability. Soil type did not affect either the type or level of germination of sclerotia. Mycelial germination was the predominant mode in sclerotia of S. minor, and it occurred between -0.03 and -0.3 MPa and 5 and 25 degrees C, with an optimum at -0.1 MPa and 15 degrees C. No germination occurred at 30 degrees C or 0 MPa. Soil temperature, moisture, or soil type did not affect the viability of sclerotia of either species. Carpogenic germination of S. sclerotiorum sclerotia, measured as the number of sclerotia producing stipes and apothecia, was the predominant mode that was affected significantly by soil moisture and temperature. Myceliogenic germination in this species under the experimental conditions was infrequent. The optimum conditions for carpogenic germination were 15 degrees C and -0.03 or -0.07 MPa. To study the effect of sclerotial size on carpogenic germination in both S. minor and S. sclerotiorum, sclerotia of three distinct size classes for each species were placed in soil disks equilibrated at -0.03 MPa and incubated at 15 degrees C. After 6 weeks, number of stipes and apothecia produced by sclerotia were counted. Solitary S. minor sclerotia did not form apothecia, but aggregates of attached sclerotia readily formed apothecia. The number of stipes produced by both S. minor and S. sclerotiorum was highly correlated with sclerotial size. These results suggest there is a threshold of sclerotial size below which apothecia are not produced, and explains, in part, why production of apothecia in S. minor seldom occurs in nature.     

Effects of soil temperature, moisture, and burial depths on carpogenic germination of Sclerotinia sclerotiorum and S. minor

Extensive studies have been conducted on the carpogenic germination of Sclerotinia sclerotiorum, but carpogenic germination in S. minor has not been studied adequately. It remains unclear why apothecia of this pathogen have seldom been observed in nature. In this study, a new method was developed to produce apothecia in the absence of soil or sand, and carpogenic germination without preconditioning was recorded for 95 of the 96 S. sclerotiorum isolates tested. Carpogenic germination of the two species was compared under a variety of temperature, soil moisture, burial depths, and short periods of high temperature and low soil moisture. The optimal temperatures for rapid germination and for maximum germination rates were both lower for S. minor than for S. sclerotiorum. The temperature range for carpogenic germination was also narrower for S. minor than for S. sclerotiorum. A 5-day period at 30 degrees C, either starting on the 10th or 20th day of incubation, did not significantly affect carpogenic germination of S. sclerotiorum. For both S. minor and S. sclerotiorum, the percentage of carpogenically germinated sclerotia increased as soil water potential increased from -0.3 to -0.01 MPa. In the greenhouse, a 10- or 20-day dry period completely arrested carpogenic germination of S. sclerotiorum, and new apothecia appeared after an interval of 35 days following rewetting, similar to the initial carpogenic germination regardless of when the dry period was imposed. In naturally infested fields, the number of sclerotia in 100 cc of soil decreased as depth increased from 0 to 10 cm before tillage, but became uniform between 0 and 10 cm after conventional tillage for both species. Most apothecia of S. minor were, however, produced from sclerotia located at a depth shallower than 0.5 cm while some apothecia of S. sclerotiorum were produced from sclerotia located as deep as 4 to 5 cm. These results provide the much needed information to assess the epidemiological roles of inoculum from sexual reproduction in diseases caused by the two Sclerotinia species in different geographical regions. However, more studies on effects of shorter and incompletely dry periods are still needed to predict production of apothecia of S. sclerotiorum in commercial fields under fluctuating soil temperature and moisture.     

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.     

Forecasting Sclerotinia Disease on Lettuce: A Predictive Model for Carpogenic Germination of Sclerotinia sclerotiorum Sclerotia

ABSTRACT A predictive model for production of apothecia by carpogenic germination of sclerotia is presented for Sclerotinia sclerotiorum. The model is based on the assumption that a conditioning phase must be completed before a subsequent germination phase can occur. Experiments involving transfer of sclerotia from one temperature regime to another allowed temperature-dependent rates to be derived for conditioning and germination for two S. sclerotiorum isolates. Although the response of each isolate to temperature was slightly different, sclerotia were fully conditioned after 2 to 6 days at 5 degrees C in soil but took up to 80 days at 15 degrees C. Subsequent germination took more than 200 days at 5 degrees C and 33 to 52 days at 20 degrees C. Upper temperature thresholds for conditioning and germination were 20 and 25 degrees C, respectively. A predictive model for production of apothecia derived from these data was successful in simulating the germination of multiple burials of sclerotia in the field when a soil water potential threshold of between -4.0 and -12.25 kilopascals (kPa) was imposed. The use of a germination model as part of a disease forecasting system for Sclerotinia disease in lettuce is discussed.     

Impact of consumer-driven changes to crop production practices on lettuce drop caused by Sclerotinia sclerotiorum and S. minor

Increasing demands for value-added salad products have triggered revolutionary changes in the production practices of vegetable salad crops in recent years. One of the pivotal changes is the adaptation of 2-m-wide beds for increased vegetable biomass per unit area. The move away from the traditional 1-m-wide raised beds in cool-season vegetable production and the associated irrigation practices potentially can have a major influence on diseases affecting cool-season vegetables. To assess the potential impacts of this shift on lettuce drop caused by Sclerotinia minor and S. sclerotiorum, the two bed widths and different irrigation frequencies within each were compared in two separate field experiments over four lettuce crops in 2 years. Treatments included 1- and 2-m bed widths with twice-weekly, weekly and biweekly drip irrigation serving as subplot treatments that were begun immediately following thinning. Incidence of lettuce drop was evaluated weekly thereafter until maturity. For S. sclerotiorum, 36 half-liter soil samples were also collected once each season and assayed for the number of sclerotia, and apothecia were counted weekly in a 10-m(2) area for each plot. Regardless of the species, the effects of bed width and irrigation frequency were both significant. Twice-weekly irrigation and 2-m bed width resulted in higher lettuce drop incidence than other treatments. For S. sclerotiorum, twice-weekly irrigation and 2-m bed width also significantly increased the number of apothecia per unit area and the accumulation of soilborne sclerotia over multiple cropping seasons. Results demonstrated that the 2-m bed width combined with the practiced frequency of irrigations can result in higher lettuce drop caused by S. minor and increased incidence of airborne infection by S. sclerotiorum in the Salinas Valley where, historically, it has not been a serious threat. Increased incidence of S. sclerotiorum infection in commercial lettuce fields in the Salinas Valley between 2001 and 2006 validates these experimental results. These relatively new crop production practices can alter the balance of the two Sclerotinia spp. that has long existed in California.     

Glasshouse trials of Coniothyrium minitans and Trichoderma species for the biological control of Sclerotinia sclerotiorum in celery and lettuce

Coniothyrium minitans, Trichoderma harzianum (HH3) and Trichoderma sp. (B1) were tested for ability to control disease caused by Sclerotinia sclerotiorum in a sequence of a celery crop and two lettuce crops in the glasshouse. In control plots, over 80% of celery and 90 and 60% of lettuce in first and second crops, respectively, were infected at harvest. Only the C. minitaris treatment in the first lettuce crop decreased disease and increased marketable yield. Nevertheless, C. minitans reduced the number of sclerotia recovered at harvest in the celery and first lettuce crops and decreased sclerotial survival over the autumn fallow periods following the celery and second lettuce crop. C. minitans survived in soil for over 1 year and spread to infect sclerotia in virtually all other plots. C. minitans infected sclerotia at all times of the year but sclerotia still failed to degrade during the summer months when the soil was dry. The Trichoderma species tested had no effect on disease and almost no effect on the survival of the sclerotia. even though they could be recovered from soil for the duration of the experiments.     

Antagonistic activity of fungi isolated from sclerotia of Sclerotinia sclerotiorum

Fungi isolated from soils in central Italy by a baiting technique with sclerotia of Sclerotinia sclerotiorum were evaluated for their antagonism in vitro to this fungus using dual cultures and tests with sclerotia. Trichoderma spp., Coniothyrium minitans and species of Fusarium and Penicillium all showed strong antagonistic activity. Morphological alterations were observed in the mycelium of S. sclerotiorum. Trichoderma spp. and Gliocladium catenulatum killed a very high percentage (96–100%) of the sclerotia.     

盾壳霉对核盘菌的拮抗作用研究

系统研究了菌核重寄生菌盾壳霉对核盘菌的拮抗作用,结果表明:盾壳霉可在核盘菌菌落上寄生,使核盘菌菌丝消解、原生质泄露,并抑制菌核的形成;而且盾壳霉提前6d接种,其分泌的抗生物质还可抑制核盘菌菌丝生长,并产生明显抑菌带。盾壳霉孢子液喷雾处理也证明:盾壳霉分生孢子即可在核盘菌子囊盘(柄)上萌发、寄生,使子囊盘(柄)萎缩枯死,而且还可以在核盘菌菌落上萌发、寄生,消解破坏菌丝体、抑制的菌核形成。     

Forecasting sclerotinia disease on lettuce: toward developing a prediction model for carpogenic germination of sclerotia

ABSTRACT The feasibility of developing a forecasting system for carpogenic germination of Sclerotinia sclerotiorum sclerotia was investigated in the laboratory by determining key relationships among temperature, soil water potential, and carpogenic germination for sclerotia of two S. sclerotiorum isolates. Germination of multiple burials of sclerotia to produce apothecia also was assessed in the field with concurrent recording of environmental data to examine patterns of germination under different fluctuating conditions. Carpogenic germination of sclerotia occurred between 5 and 25 degrees C but only for soil water potentials of >/=-100 kPa for both S. sclerotiorum isolates. Little or no germination occurred at 26 or 29 degrees C. At optimum temperatures of 15 to 20 degrees C, sclerotia buried in soil and placed in illuminated growth cabinets produced stipes after 20 to 27 days and apothecia after 27 to 34 days. Temperature, therefore, had a significant effect on both the rate of germination of sclerotia and the final number germinated. Rate of germination was correlated positively with temperature and final number of sclerotia germinated was related to temperature according to a probit model. Thermal time analysis of field data with constraints for temperature and water potential showed that the mean degree days to 10% germination of sclerotia in 2000 and 2001 was 285 and 279, respecttively, and generally was a good predictor of the observed appearance of apothecia. Neither thermal time nor relationships established in the laboratory could account for a decline in final percentage of germination for sclerotia buried from mid-May compared with earlier burials. Exposure to high temperatures may explain this effect. This, and other factors, require investigation before relationships derived in the laboratory or thermal time can be incorporated into a forecasting system for carpogenic germination.     

Bacillus thuringiensis C25 which is rich in cell wall degrading enzymes efficiently controls lettuce drop caused by Sclerotinia minor

European Journal of Plant Pathology - Sclerotinia is a phytopathogenic genus of fungi that form sclerotia: black, hard, seed-like functioning bodies. Sclerotinia sclerotiorum and Sclerotinia minor...     

The effects of soil solarization on sclerotial populations of Sclerotinia sclerotiorum

Solarization reduced the populations of sclerotia of Sclerotinia sclerotiorum in soil and reduced the ability of the surviving sclerotia to form apothecia. The greatest reductions occurred in the top 5 cm layer of soil but significant effects were seen at 10 and 15 cm depths. These reductions were due mainly to microbial colonization and degradation of sclerotia weakened by the sublethal temperatures produced by solarization. A beneficial side-effect was a significant reduction in the population of weeds in solarized plots.     

油菜菌核病内生拮抗细菌的筛选及防病作用研究

以油菜菌核病菌Sclerotinia sclerotiorum为靶标菌,测定了63株内生细菌对其菌丝生长、菌核形成及萌发的抑制作用。结果表明:在所有供试菌株中,除1株未表现出抑菌活性外,其余菌株均有抑菌作用,其中有6.3％的菌株抑菌带大于10 mm,7株细菌可完全抑制病原菌的菌核形成,1株细菌可完全抑制菌核萌发;此外,结合生物测定结果,从中筛选到1株对油菜菌核病的高效生防菌株Em7,其无菌培养滤液对温室苗期油菜菌核病的防治效果可达97.5％。通过形态特征、生理生化特性及16S rDNA序列分析,认为该菌株属于枯草芽孢杆菌Bacillus subtilis。于接种病菌前后不同时间喷施菌株Em7无菌培养滤液,对油菜菌核病均有防治效果,但防效之间差异显著,以接种病菌前24 h喷施防效最高。原液及不同稀释度无菌培养滤液对菌丝生长、菌核萌发及病害防治的效果明显不同,随着稀释度的增加,其抑菌效果降低。显微观察结果表明,菌株Em7对油菜菌核病菌菌丝的生长与发育会产生明显影响,可致使菌丝畸形、皱缩及细胞质外渗。     

Effect of inoculum type and timing of application of Coniothyrium minitans on Sclerotinia sclerotiorum: influence on apothecial production

The effects of different inocula of the mycoparasite Coniothyrium minitans on carpogenic germination of sclerotia of Sclerotinia sclerotiorum at different times of year were assessed. A series of three glasshouse box bioassays was used to compare the effect of five spore-suspension inocula of C. minitans , including three different isolates (Conio, IVT1 and Contans), with a standard maizemeal–perlite inoculum. Apothecial production, as well as viability and C. minitans infection of S. sclerotiorum sclerotia buried in treated soil, were assessed. Maizemeal–perlite inoculum at 10⁷ CFU per cm³ soil reduced sclerotial germination and apothecial production in all three box bioassays, decreasing sclerotial recovery and viability in the second bioassay and increasing C. minitans infection of sclerotia in the first bioassay. Spore-suspension inocula applied at a lower concentration (10⁴ CFU per cm³ soil) were inconsistent in their effects on sclerotial germination in the three box bioassays. Temperature was an important factor influencing apothecial production. Sclerotial germination was delayed or inhibited when bioassays were made in the summer. High temperatures also inhibited infection of sclerotia by C. minitans . Coniothyrium minitans survived these high temperatures, however, and infected the sclerotia once the temperature decreased to a lower level. Inoculum level of C. minitans was an important factor in reducing apothecial production by sclerotia. The effects of temperature on both carpogenic germination of sclerotia and parasitism of sclerotia by C. minitans are discussed.     

Interactions Between the Mycoparasite Pythium oligandrum and Sclerotia of the Plant Pathogen Sclerotinia sclerotiorum

Pythium oligandrum Drechsler is a mycoparasite which parasitizes hyphae of many fungal species. A detailed study of the interactions between P. oligandrum and the sclerotia of the plant pathogen Sclerotinia sclerotiorum (Lib.) de Bary is presented. Pythium oligandrum was present in Danish soils at concentrations between 4 and 26 cfu g^–1 soil. An increase in the natural population of P. oligandrum by addition of P. oligandrum zoospores to a soil reduced the ability of sclerotia of S. sclerotiorum to germinate myceliogenically and the sclerotia were colonized internally by P. oligandrum. This colonization and reduction of germination of sclerotia were also seen when sclerotia and P. oligandrum were incubated together in water. Small sclerotia were significantly more susceptible to parasitism by P. oligandrum than large sclerotia, and increasing the incubation time caused a further reduction in the germination ability of the sclerotia. P. oligandrum was able to pass through its entire life-cycle from zoospores to oogonia both with sclerotia as sole nutrient-source and in water containing exudates from the sclerotia. The cell wall degrading enzymes N-acetyl--D-glucosaminidase (NAGase), endo-chitinase, protease, -glucanase, -glucosidase and cellobiohydrolase were detected in culture filtrates of P. oligandrum cultivated with S. sclerotiorum. These findings suggest that P. oligandrum has a potential to reduce the survival of S. sclerotiorum sclerotia present naturally in soils, through mycoparasitic activity.     

A method for inducing apothecia from sclerotia of Sclerotinia sclerotiorum

An isolate of Sclerotinia sclerotiorum from oilseed rape was grown on sterilized wheat grain for 3 weeks at 20 C, followed by 4 weeks at 4^oC. Harvested sclerotia were buried 1 cm deep in compost in plastic containers and kept at 10^oC until apothecial stipes appeared (c. 6 weeks). When these dishes were placed under near-UV light (14 h/day) at 22^oC, apothecia matured in 5 days. The method also induced apothecia from sclerotia of 35 other isolates of S. sclerotiorum obtained from 17 different hosts.     

Interactions between Coniothyrium minitans and Sclerotinia minor affect biocontrol efficacy of C. minitans

Coniothyrium minitans, marketed as Contans, has become a standard management tool against Sclerotinia sclerotiorum in a variety of crops, including winter lettuce. However, it has been ineffective against lettuce drop caused by S. minor. The interactions between C. minitans and S minor were investigated to determine the most susceptible stage in culture to attack by C. minitans, and to determine its consistency on S minor isolates belonging to four major mycelial compatibility groups (MCGs). Four isolates of S. minor MCG 1 and 5 each from MCGs 2 and 3 and one from MCG 4 were treated in culture at purely mycelial, a few immature sclerotial, and fully mature sclerotial phases with a conidial suspension of C. minitans. Sclerotia from all treatments were harvested after 4 weeks, air dried, weighed, and plated on potato dextrose agar for recovery of C. minitans. S. minor formed the fewest sclerotia in plates that received C. minitans at the mycelial stage; C. minitans was recovered from nearly all sclerotia from this treatment and sclerotial mortality was total. However, the response of MCGs was inconsistent and variable. Field experiments to determine the efficacy of C. minitans relative to the registered fungicide, Endura, on lettuce drop incidence and soil inoculum dynamics were conducted from 2006 to 2009. All Contans treatments had significantly lower numbers of sclerotia than Endura and unsprayed control treatments, and drop incidence was as low as in Endura-treated plots (P > 0.05). Although the lower levels of lettuce drop in Contans treatments were correlated with significantly lower levels of sclerotia, the lower levels of lettuce drop, despite the presence of higher inoculum in the Endura treatment, was attributable to the prevention of infection by S. minor. A useful approach to sustained lettuce drop management is to employ Contans to lower the number of sclerotia in soil and to apply Endura to prevent S. minor infection within a cropping season.     

不同核盘菌菌株及其近缘种的RAPD分析

 本文利用随机引物扩增多态性DNA (RAPD)技术分析了7个生物学性状差异较大核盘菌(Sclerotinia sclerotiorum)的遗传多样性,并同三叶草核盘菌(S.trifoliorum)、小核盘菌(S.minor)的代表性菌株和莴苣上的一种产菌核病原菌的代表菌株Let-19进行了比较。结果表明40个引物中8个引物能稳定地从供试菌株中扩增出多态性DNA片段。通过分析这些多态性片段可以看出7个供试核盘菌菌株之间的遗传相似系数变化幅度为0.505 2~0.793 1,而核盘菌、三叶草核盘菌,小核盘菌和Let-19之间的遗传相似系数的变幅则为0.194 2~0.385 3。莴苣上的菌株Let-19的RA PD图谱同供试其它种的菌株既存在明显差异的DNA片段电泳带,又显示出一些位置一致的DNA片段电泳带。因而Let-19同核盘菌属真菌的亲缘关系较近。供试的引物中OPL14既能介导从供试的7个核盘菌菌株和3个近缘种的3个菌株的DNA样品中扩增出相同的DNA片段,又能扩增出种或菌株特异性DNA片段。因而RAPD技术适于研究核盘菌的遗传多样性及分析核盘菌属真菌的亲缘关系。     

Potential for Integrated Control of Sclerotinia sclerotiorum in Glasshouse Lettuce Using Coniothyrium minitans and Reduced Fungicide Application

ABSTRACT All pesticides used in United Kingdom glasshouse lettuce production (six fungicides, four insecticides, and one herbicide) were evaluated for their effects on Coniothyrium minitans mycelial growth and spore germination in vitro agar plate tests. Only the fungicides had a significant effect with all three strains of C. minitans tested, being highly sensitive to iprodione (50% effective concentration [EC(50)] 7 to 18 mug a.i. ml(-1)), moderately sensitive to thiram (EC(50) 52 to 106 mug a.i. ml(-1)), but less sensitive to the remaining fungicides (EC(50) over 200 mug a.i. ml(-1)). Subsequently, all pesticides were assessed for their effect on the ability of C. minitans applied as a solid substrate inoculum to infect sclerotia of Sclerotinia sclerotiorum in soil tray tests. Despite weekly applications of pesticides at twice their recommended concentrations, C. minitans survived in the soil and infected sclerotia equally in all pesticide-treated and untreated control soil trays. This demonstrated the importance of assessing pesticide compatibility in environmentally relevant tests. Based on these results, solid substrate inoculum of a standard and an iprodione-tolerant strain of C. minitans were applied individually to S. sclerotiorum-infested soil in a glasshouse before planting lettuce crops. The effect of a single spray application of iprodione on disease control in the C. minitans treatments was assessed. Disease caused by S. sclerotiorum was significantly reduced by C. minitans and was enhanced by a single application of iprodione, regardless of whether the biocontrol agent was iprodione-tolerant. In a second experiment, disease control achieved by a combination of C. minitans and a single application of iprodione was shown to be equivalent to that of prophylactic sprays with iprodione every 2 weeks. The fungicide did not affect the ability of C. minitans to spread into plots where only the fungicide was applied and to infect sclerotia. These results indicate that integrated control of S. sclerotiorum with soil applications of C. minitans and reduced foliar iprodione applications was feasible, did not require a fungicide tolerant isolate, and that suppression of Sclerotinia disease by C. minitans under existing chemical control regimes has credence.     

山东省不同地区蔬菜菌核病菌对四霉素的敏感性

采用菌丝生长速率法测定了四霉素对采自山东省不同地区不同蔬菜作物的151株菌核病菌的毒力作用,同时比较了其对蔬菜菌核病菌不同生育阶段的抑制活性,并通过离体叶片法评价了四霉素对蔬菜菌核病的防治效果。结果表明:菌核病菌对四霉素比较敏感,敏感性频率呈单峰正态分布,151株病菌菌丝生长的平均EC₅₀值为 (0.29 ± 0.01) μg/mL,该值可作为蔬菜菌核病菌对四霉素的敏感基线。此外,经四霉素处理后,该病菌的菌核数量以及干重明显降低,菌核明显变小;2 μg/mL的处理对菌核萌发的抑制率达到100.00%。 离体黄瓜叶片接种试验表明,四霉素对菌核病具有较好的保护和治疗效果,且保护作用较为显著。在质量浓度为20 μg/mL时,四霉素对该病的防效显著高于对照药剂多菌灵和异菌脲。因此,四霉素具有防治蔬菜菌核病的潜在价值,可进一步通过田间试验验证其应用效果。