K.L. Bailey

Survival of leaf spot pathogens on crop residues of wheat and barley in Saskatchewan.

Pycnidia of Stagonospora nodorum, and pseudothecia of Phaeosphaeria nodorum and Pyrenophora triticirepentis occurred in greater numbers after one overwintering period on residues of wheat and barley stored on the surface of the soil than on residues from the previous fall. Conidial numbers of Bipolaris sorokiniana and Drechslera teres on residues of wheat and barley, and pseudothecia of Pyrenophora teres on residues of barley decreased over one winter but these pathogens continued to sporulate at low levels after two winters. With residue from the soil surface, Drechslera teres and B. sorokiniana conidia occurred in greater numbers on lower parts of the plants. Drechslera teres occurred primarily on leaf and sheath areas and B. sorokiniana, on sheath and stem areas, while P. teres sporulated mainly on stems. Numbers of conidia of D. teres may have declined because the pathogen occurred mainly on leaves, which disintegrated after one winter. The wheat pathogen Stagonospora nodorum was able to sporulate on ...

Screening of adjuvants for bioherbicide formulations with Colletotrichum spp. and Phoma spp.

Abstract A study was conducted to determine whether certain surfactants (Tween series: 20, 40, 80, and Tergitol NP series: 9, 10) and adjuvants (sorbitol and gelatin) would be useful components in bioherbicide formulations of Colletotrichum (10 isolates) and Phoma (5 islolates). The effect of adjuvants on conidial germination and mycelial growth varied with adjuvant, adjuvant concentration (0.01, 0.1, 1, and 5%), fungal isloates, and conidial density (105–108 conidia/ml). Tween 20 reduced germination and mycelial growth in some Phoma and all Colletotrichum isolates, whereas Tween 40 and Tween 80 stimulated germination without detrimental effects on mycelial growth of all isolates. Tween 40 and Tween 80 released conidia from self-inhibition of germination in Colletotrichum as compared to the germination of conidia at 107 conidia/ml in the absence of the adjuvant. Tergitol NP often reduced germination and mycelial growth. There were no trends in fungal responses to sorbitol. The responses of Colletotrichum were highly variable to gelatin, but for Phoma, gelatin increased germination and mycelial growth, and also released self-inhibition of germination. In summary, gelatin, Tween 40, and Tween 80 were useful components for bioherbicide formulations to increase conidial germination and mycelial growth of Phoma, whereas Tween 40 and Tween 80 were useful for Colletotrichum.

The infection process of Alternaria cirsinoxia on Canada thistle (Cirsium arvense) and host structural defence responses

The infection process of Alternaria cirsinoxia was studied on Canada thistle (Cirsium arvense) in the controlled environment and in the field. In the controlled environment, germination of conidia began at 2 h and appressoria formation at 4 h after inoculation. Approximately 75% of appressoria formed at the anticlinal wall junctions of the epidermis. Leaf penetration occurred between 6 and 24 h, most commonly in between adjoining anticlinal walls. Penetration through stomata was rare. After penetration, large, intracellular infection hyphae formed and branched within epidermal cells, ramifying throughout the leaf tissues inter- and intracellularly by 24 h. In field conditions, infection coincided with prolonged rainfall and conidia remained viable on the leaf surface for 8–9 days (d) before causing infection on leaves. A host response occurred after penetration, involving deposition of lignin and callose in the infected epidermal and mesophyll cell walls. High levels of silicon were detected in epidermal cells directly below appressoria, often appearing to form entirely silicified infected cells which were resistant to collapse after air-drying. This study shows that A . cirsinoxia has the potential for rapid invasion of the leaf tissues of Canada thistle under good moisture conditions. The implications of the host responses, in terms of defence against infection, are discussed.

Colletotrichum sp: A potential candidate for biocontrol of scentless chamomile (Matricaria perforata) in western Canada

Abstract Based on an assessment of 706 fungal isolates obtained from Canada and Europe, a group of Colletotrichum sp. isolates, tentatively identified as C. truncatum, was moderately efficacious for biocontrol of scentless chamomile (Matricaria perforata). In this study, 19 C. truncatum isolates, 11 from Canada and eight from Europe, were compared for virulence, crop safety, and minimum dew requirement for infection to narrow the selection of candidates. Applied at 1×106 spores mL−1, these isolates expressed variable virulence under controlled environments, with slightly higher variations observed on the Canadian isolates. There was also a slight difference in host specificity among the isolates tested; most isolates caused disease only on chamomile species (M. perforata and M. recutita) but two Canadian isolates also infected lentil, flax, or both. At 20°C, most isolates required more than 20 h dew for maximum infection. This requirement can be an impediment for using this fungus as a biocontrol agent in western Canada where the climate is semi-arid. Treatment of scentless chamomile at the 10-leaf stage with the herbicide metribuzin 48 h prior to fungal inoculation increased weed control to 72%, compared to 40 and 47% by the herbicide and fungus applied alone. However, a similar treatment using the herbicide bentazon did not enhance the weed control significantly as compared to the herbicide alone.

Canadian innovations in microbial biopesticides.

For many years, researchers have been sceptical as to whether microbial biological control agents, and in particular biopesticides, would be developed for use in areas other than greenhouses and forestry. This perception is slowly changing as the increased development and use of biopesticides in Canada is moving from being a novelty to a reality. This paper examines the role of biopesticides in Canada and the nine stages required to take a microbial biopesticide from discovery through product development, striving for commercialization and adoption by the end user. It highlights examples of Canadian biopesticide innovations that have moved through the innovation chain, illustrating the challenges and rewards along the way.

Microbial weed control: an off-beat application of plant pathology

In plant pathology, a thorough understanding of pathogen–host–environment interactions is required to develop disease control methods that will be detrimental to the pathogen and ultimately protect the plant. The same disease-conducive conditions can be utilized in a nontraditional way, as with the bioherbicide approach to weed control, to benefit the pathogen and cause harm to the plant. Potential biocontrol organisms should be investigated for the six following aspects to determine their biological and ecological characteristics: (i) identification of the causal agent, (ii) pathogenicity and disease development on a range of plant species, (iii) pathogen mechanisms involved in infection of the host, (iv) potential plant defense responses, (v) genetic variability in the pathogen and the host, and (vi) environmental influences on the host and the pathogen. The potential of plant pathogens as bioherbicides is described using Alternaria cirsinoxia for control of Canada thistle (Cirsium arvense) as a case study.

Effect of dew temperature, post-inoculation condition, and pathogen dose on suppression of scentless chamomile by Colletotrichum truncatum

Abstract Scentless chamomile, a noxious weed in western Canada, has a high natural tolerance to many herbicides. Colletotrichum truncatum, a host specific fungal pathogen, is suppressive to scentless chamomile when applied inundatively. A broadcast application was used at 200 L ha−1 to evaluate biocontrol potential of this pathogen under a range of dew temperatures (DT), post-inoculation conditions (PIC), and pathogen doses (PD). A DT between 20 and 25°C was more conducive to infection, resulting in higher levels of disease and weed suppression as compared to 15 and 30°C. Under similar post-inoculation temperature regimes, disease was only slightly more severe in growth chambers than in the greenhouse. There was a positive linear relationship between the PD and weed suppression. An inoculum concentration >1×108 spores mL−1 reduced plant fresh weight by approximately 50% when compared to untreated controls. These results indicate that biocontrol of scentless chamomile using C. truncatum in the semi-arid Canadian prairies will likely encounter frequent non-favourable field conditions.

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.

Effect of Epidemiological Factors on the Impact of the Fungus Plectosporium tabacinum on False Cleavers ( Galium spurium )

The fungus Plectosporium tabacinum has been evaluated as a bioherbicide for control of false cleavers ( Galium spurium ), but the limiting factors and optimal conditions for successful control using this pathogen are not known. False cleavers mortality and dry weight reductions caused by P. tabacinum were assessed under single or combined factors, including pathogen inoculum concentration, plant growth stage, dew period (duration, frequency, and timing), and dew period temperature. The minimum inoculum concentration required to kill false cleavers seedlings was 1 2 10 7 conidia mL -1 at an application rate of 150 mL m -2 . False cleavers seedlings in the cotyledon or 1-whorl growth stage were the most susceptible. Increasing inoculum concentration increased weed control efficacy on older false cleavers seedlings. When an adequate dew period was provided, 100% mortality and dry weight reduction occurred. The minimum dew period to achieve 100% mortality was 16 h. Delaying the initiation of the dew period by 24 h significantly reduced disease development. Short, repetitive dew periods only improved false cleavers control to a limited extend and the length of initial dew is a critical factor influencing false cleavers mortality due to P. tabacinum . The optimal dew period temperature for disease development was above 15°C.

Biological and genetic characterisation of Phoma macrostoma isolates with bioherbicidal activity

Abstract The fungus Phoma macrostoma Mont. isolate 94-44B was registered as a bioherbicide for control of broadleaved weeds in Canada and the USA in 2011 and 2012, respectively. To obtain the registrations, the fungus had to be characterised both biologically and genetically. The objectives of this study were to demonstrate that bioherbicidal activity was associated with specific genetic markers and to determine whether bioherbicidal activity was a general trait of the species or only selected isolates. A collection of 64 isolates of P. macrostoma was established. A greenhouse bioassay and bioherbicidal-specific primers were used to determine bioherbicidal activity of all isolates. Only isolates originating from Canada thistle demonstrated the ability to reduce dandelion seedlings and display the 853 bp amplicon for the bioherbicidal-specific primer. Bioherbicidal isolates were consistently differentiated from all other isolates with two main genotypic groupings (I and II) arising from internal transcribed spacer (ITS) and amplified fragment length polymorphisms (AFLP) sequence analyses. Using AFLP, two biotypes of bioherbicidal isolates were also differentiated by the presence or absence of an AFLP marker at a single polymorphic locus. The genetic divergence among the bioherbicidal and nonbioherbicidal isolates of P. macrostoma was only 2.21% which was lower than that reported for other related Phoma sp. Other than the bioherbicidal trait, there was no apparent affiliation of the genetics with known varietal types, host or geographic origin. ITS sequence analysis and AFLP fingerprinting may be used as tools to detect bioherbicidal isolates of P. macrostoma.