J. Derby

Infection process of Colletotrichum gloeosporioides f. sp. malvae on Malvaceae weeds

Colletotrichum gloeosporioides f. sp. malvae is highly pathogenic on Malva pusilla and Malva parviflora but not on Malva neglecta and Abutilon theophrasti . Germination of conidia was higher on agar discs than on leaf surfaces of the Malvaceae hosts and safflower. Germination, however, was considerably reduced on agar discs when the number of conidia applied was increased. Timing of the germination process and morphology of pre-penetration structures were similar on the leaf surface of the five host species examined. Slightly more than 4% of melanized appressoria developed infection structures within epidermal cells of M. pusilla, A. theophrasti and safflower. Levels of penetration were lower ( M. parviflora and M. neglecta. Colletotrichum gloeosporioides f. sp. malvae penetrated plant cuticles directly and produced infection structures within epidermal cells 31–36 h after inoculation. The mode of infection of C. gloeosporioides f. sp. malvae involved intracellular vesicles, large-diameter primary hyphae that constricted at transcellular penetration sites and secondary hyphae. Development of primary hyphae and production of secondary hyphae was extensive on the susceptible hosts M. pusilla and M. parviflora . In the moderately resistant hosts M. neglecta and A. theophrasti colonization was stopped by a hypersensitive reaction of cells adjacent to initial infection sites and no secondary hyphae were produced. Our study strongly suggests that determinants of host-pathogen compatibility or incompatibility do not operate during the pre-penetration phase of C. gloeosporioides f. sp. malvae , but are activated a few days after successful penetration.

Effect of spraying adjuvants with the biocontrol fungus Microsphaeropsis ochracea at different water volumes on the colonization of apple leaves

Abstract In a previous study, it was observed that Microsphaeropsis ochracea was less efficacious as a biofungicide for apple scab when applied under field conditions as an unformulated spore suspension with an airblast spray using low water volumes as compared to a ground cover spray using high water volumes. The effect of spore concentration (109 to 1012 spores ha−1), water volume (250–1500 L ha−1), and 20 adjuvants were studied to improve colonization of apple leaves by M. ochracea. Using commercial-type spray equipment, the fungus was applied to excised apple leaves. Higher spores concentrations resulted in greater colonization. Water volume did not have a strong impact on colonization. Only a few adjuvants improved germination (glycerine) and mycelial growth (K-90, Agrimer, Ekol, and Tween 80) in some trials. When tested on apple trees, the adjuvant Assist provided the most consistent improvement in colonization in five out of eight trials. The use of oils, humectants, and surfactants could broaden the opportunities for using this biofungicide.

Optimising inoculum yield and shelf life of Plectosphaerella cucumerina, a potential bioherbicide for Cirsium arvense

ABSTRACT Plectosphaerella cucumerina was identified as a potential bioherbicide for controlling Cirsium arvense in Canada and New Zealand. The current study evaluated production conditions using two isolates (one from each country) to determine whether the yield and shelf life of inoculum are suitable for mass production. Mycelial growth and sporulation in culture both increased from 15°C to 25°C and declined at higher temperatures with no mycelial growth at 37°C. The Canadian isolate produced fewer conidia than a New Zealand isolate. Potato dextrose-based liquid media with moderate to high concentrations of carbohydrates (25%, 50%, and 100%) maximised conidia production and these base media produced conidia with the highest germination rate (>80%) both at harvest and after 4 weeks stored at 4°C in 2.5% glycerol, 40% milk glycerol or after air drying. However, after 10-week storage, the conidia failed to germinate. Sporulation occurred during growth on all solid substrates tested (rice, rolled barley, and triticale), but conidial germination was highest on rice and barley, both before and after air drying. By contrast to conidia, 90% of mycelia-infested barley grains were viable after 3 years of storage at room temperature, although viability was lost by this time on the other substrates. This study has shown that the nutritional base is an important determinant of sporulation and shelf life for P. cucumerina. Although the yield of conidia in liquid medium was adequate to justify further development of P. cucumerina as a bioherbicide, improvement in its shelf life, or alternate formulation types that extend the shelf life, must be made for commercial efficiency.

In vivo studies evaluating commercial biofungicide suppression of blight caused by Phytophthora ramorum in selected ornamentals

Abstract Phytophthora ramorum is a regulated pathogen in North America, which causes ramorum blight on nursery stock resulting in the implementation of costly quarantine and eradication measures. Earlier studies showed some biofungicides could inhibit growth and reduce the disease in vitro. The objective of this study was to evaluate the effect of commercial biofungicides on in vivo disease development and plant growth on four nursery species when inoculated with three isolates representing each of the NA1, NA2 and EU1 lineages of the pathogen. The plant species were Gaultheria shallon, Rubus spectabilis, Rhododendron caucasicum x R. ponticum var. album and Cornus sericea. Prior to pathogen inoculation, plants were pretreated with Aliette® (standard fungicide), Actigard 50WG Plant Activator®, Actinovate® SP, Sonata®, Serenade®, Plant Helper®, SoilGard® 12G and Pro Mix BX Biofungicide™. A suspension containing 7000 sporangia ml−1 was used to inoculate plants. Disease severity and foliar biomass were recorded 14 days after inoculation. Actinovate was the only product able to reduce disease severity by about 50% and improve plant growth of the susceptible hosts. Its effectiveness differed by isolate. Several other biofungicides and the standard fungicide provided suppression of disease and improved plant growth but their effectiveness was dependent on host species, product and isolate. None of the products prevented disease and generally the level of control obtained was lower than would be acceptable for a commercial nursery. In addition to assessing the disease control products, it was also observed that rhododendron, salal and salmonberry were highly susceptible hosts of P. ramorum with PR05-001 (NA2) being the most aggressive isolate on them.