Biocontrol of Botrytis cinerea by Ulocladium atrum in Different Production Systems of Cyclamen

Brazilian isolates of Clonostachys rosea: colonization under different temperature and moisture conditions and temporal dynamics on strawberry leaves

AIMS

In a research programme for managing diseases caused by Botryis cinerea, four isolates of the antagonistic fungus Clonostachys rosea (Cr) were obtained from different ecosystems in Brazil. We studied ecological requirements for the colonization of strawberry leaves by these isolates.

METHODS AND RESULTS

Temperature effects on both mycelial growth in vitro and leaf colonization by Cr were studied. At 10 degrees C, growth on potato dextrose agar and colonization of leaf discs were poor. Optimum temperature for mycelial growth and leaf colonization was around 25 degrees C. The isolates were applied to leaves which were exposed to 0-48 h intervals of moisture. They were also applied to leaves which remained from 0 to 36 h without wetness. All isolates efficiently colonized leaves, regardless of moisture interval or the delay to begin wetness. Although all isolates survived in green leaves of whole plants, colonization decreased throughout a 49-day period.

CONCLUSIONS

Brazilian isolates of Cr can establish and colonize strawberry leaves under a wide range of temperature and moisture conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is expected that the Brazilian isolates of Cr will establish efficiently in strawberry leaves where they can compete with B. cinerea.

Suppression of Botrytis Blight of Begonia by Trichoderma hamatum 382 in Peat and Compost-Amended Potting Mixes

Inoculation of an industry standard light sphagnum peat potting mix with Trichoderma hamatum 382 (T382) significantly (P = 0.05) reduced the severity of Botrytis blight, caused by Botrytis cinerea, on begonia plants grown in a greenhouse. In data combined from three experiments, the degree of control provided by T382 did not differ significantly (P = 0.05) from that provided by weekly topical sprays with chlorothalonil. In addition, T382 significantly (P = 0.05) increased shoot dry weight and salability of flowering plants. Incorporation of composted cow manure (5%, vol/vol) into the light peat mix also significantly (P = 0.05) decreased blight severity while shoot dry weight and salability were increased. Blight severity on plants in this compost mix did not differ significantly (P = 0.05) from that on those in the light peat mix inoculated with T382. Finally, T382 and chlorothalonil did not significantly (P = 0.05) affect blight severity, shoot dry weight, or salability of plants grown in the compost mix. Spatial separation was maintained in begonias between the biocontrol agent T382 and the pathogen. It was concluded, therefore, that the decrease in disease severity provided by inoculation of the peat mix with T382 most likely was due to systemic resistance induced in begonia against Botrytis blight. The suppressive effect of the compost mix against Botrytis blight was unusual because composts typically do not provide such effects unless inoculated with a biocontrol agent capable of inducing systemic resistance in plants to disease.

Modeling Spatial Characteristics in the Biological Control of Fungi at Leaf Scale: Competitive Substrate Colonization by Botrytis cinerea and the Saprophytic Antagonist Ulocladium atrum

ABSTRACT A spatially explicit model describing saprophytic colonization of dead cyclamen leaf tissue by the plant-pathogenic fungus Botrytis cinerea and the saprophytic fungal antagonist Ulocladium atrum was constructed. Both fungi explore the leaf and utilize the resources it provides. Leaf tissue is represented by a two-dimensional grid of square grid cells. Fungal competition within grid cells is modeled using Lotka-Volterra equations. Spatial expansion into neighboring grid cells is assumed proportional to the mycelial density gradient between donor and receptor cell. Established fungal biomass is immobile. Radial growth rates of B. cinerea and U. atrum in dead cyclamen leaf tissue were measured to determine parameters describing the spatial dynamics of the fungi. At temperatures from 5 to 25 degrees C, B. cinerea colonies expanded twice as rapidly as U. atrum colonies. In practical biological control, the slower colonization of space by U. atrum thus needs to be compensated by a sufficiently dense and even distribution of conidia on the leaf. Simulation results confirm the importance of spatial expansion to the outcome of the competitive interaction between B. cinerea and U. atrum at leaf scale. A sensitivity analysis further emphasized the importance of a uniform high density cover of vital U. atrum conidia on target leaves.

Commercialization and implementation of biocontrol

Although the number of biocontrol products is increasing, these products still represent only about 1% of agricultural chemical sales. Yet these are important contributions because biocontrol agents offer disease management alternatives with different mechanisms of action than chemical pesticides. Trends in research include the increased use of biorational screening processes to identify microorganisms with potential for biocontrol, increased testing under semicommercial and commercial production conditions, increased emphasis on combining biocontrol strains with each other and with other control methods, integrating biocontrol into an overall system.

Biological Control of Blossom Blight of Alfalfa Caused by Botrytis cinerea Under Environmentally Controlled and Field Conditions

Fungal and bacterial antagonists were tested for their inhibition of sporulation of Botrytis cinerea on detached alfalfa florets. Clonostachys rosea, Gliocladium catenulatum, and Trichoderma atroviride were evaluated for protecting young blossoms and pods of alfalfa from infection by B. cinerea in vitro. C. rosea was further tested to control pod rot and seed rot caused by B. cinerea under field conditions. The results showed that four of the tested antagonists, C. rosea, G. catenulatum, T. atroviride, and Trichothecium roseum, could inhibit sporulation by B. cinerea on detached alfalfa florets. Both C. rosea and G. catenulatum were effective in suppression of infection of alfalfa pods by B. cinerea when inoculated on fresh petals of alfalfa at the anthesis stage, and their efficacy was greater than that of Trichoderma atroviride. A significant suppression of B. cinerea by C. rosea and G. catenulatum on pods and seed of alfalfa was observed when they were inoculated on senescent petals at the pod-development stage. Results of a field trial indicated that C. rosea applied to upper parts of alfalfa plants significantly suppressed pod rot and seed rot caused by B. cinerea, and significantly increased seed production of alfalfa in each of 3 years. These studies show that C. rosea has potential as a biocontrol agent for control of alfalfa blossom blight caused by B. cinerea.

Effect of Formulated Yeast in Suppressing the Liberation of Botrytis cinerea Conidia

Eight yeast isolates that bound directly to Botrytis cinerea germlings were assessed for the ability to suppress spore liberation of conidia from B. cinerea. After the yeast cell suspension from each isolate was mixed with cellulose and dried, the product was milled into a fine powder. This yeast-cellulose formulation was applied as a dry powder to sporulating B. cinerea colonies on kiwifruit (Actinidia deliciosa) leaf disks, where the particles from the formulation attached to conidiophores and conidia. Some of these formulations significantly suppressed the liberation of conidia from treated colonies. Suppression of conidial liberation could provide another management tool for the biological control of sporulating B. cinerea with applications during late epidemic development. Using α-cellulose prepared with Candida pulcherrima in the conditions imposed in the present study, there was an approximately 50% reduction in the number of conidia released with the treatment of the B. cinerea lesions. The suppression of disease through a reduction in the population of liberated conidia is discussed.

Sensitivity of Ulocladium atrum, Coniothyrium minitans, and Sclerotinia sclerotiorum to benomyl and vinclozolin

Assays on mycelial growth and spore germination were carried out to determine the sensitivity of the biocontrol agents Ulocladium atrum and Coniothyrium minitans and the plant pathogen Sclerotinia sclerotiorum to benomyl and vinclozolin. Ulocladium atrum was more tolerant to these fungicides than C. minitans and S. sclerotiorum. The 50% effective concentration (EC50) of U. atrum based on the mycelial growth inhibition was 1467.3 µg active ingredient (a.i.)/mL for benomyl and 12.6 µg a.i./mL for vinclozolin, and the maximum inhibition concentration was higher than 4000 µg a.i./mL for both fungicides. For C. minitans and S. sclerotiorum, however, the EC50 based on mycelial growth inhibition was lower than 1 µg a.i./mL. After incubation for 24 h at 20°C, the germination rate of U. atrum conidia was 90–99% on potato dextrose agar (PDA) amended with benomyl at 100–500 µg a.i./mL or vinclozolin at 10–500 µg a.i./mL. At these concentrations, germ tubes of U. atrum developed into long, branched hyphae in benomyl treatments, but they remained short and clustered in vinclozolin treatments. Pycnidiospores of C. minitans and ascospores of S. sclerotiorum germinated on PDA amended with benomyl at 100–500 µg a.i./mL, but the germ tubes did not grow further. Spore germination of C. minitans and S. sclerotiorum was less than 3.2% on PDA amended with vinclozolin at 10–500 µg a.i./mL after 24 h. This is the first report on the sensitivity of U. atrum and C. minitans to benomyl and vinclozolin. The results suggest that it is possible to control S. sclerotiorum using a combination of U. atrum and benomyl or vinclozolin.Key words: fungicides, mycelial growth, spore germination, integrated pest management.

Biological control in greenhouse systems

The controlled environment of greenhouses, the high value of the crops, and the limited number of registered fungicides offer a unique niche for the biological control of plant diseases. During the past ten years, over 80 biocontrol products have been marketed worldwide. A large percentage of these have been developed for greenhouse crops. Products to control soilborne pathogens such as Sclerotinia, Pythium, Rhizoctonia and Fusarium include Coniothyrium minitans, species of Gliocladium, Trichoderma, Streptomyces, and Bacillus, and nonpathogenic Fusarium. Products containing Trichoderma, Ampelomyces quisqualis, Bacillus, and Ulocladium are being developed to control the primary foliar diseases, Botrytis and powdery mildew. The development of Pseudomonas for the control of Pythium diseases in hydroponics and Pseudozyma flocculosa for the control of powdery mildew by two Canadian research programs is presented. In the future, biological control of diseases in greenhouses could predominate over chemical pesticides, in the same way that biological control of greenhouse insects predominates in the United Kingdom. The limitations in formulation, registration, and commercialization are discussed, along with suggested future research priorities.