Role of Ascospores in Further Spread of QoI-Resistant Cytochrome b Alleles (G143A) in Field Populations of Mycosphaerella graminicola

ABSTRACT Strobilurin fungicides or quinone outside inhibitors (QoIs) have been used successfully to control Septoria leaf blotch in the United Kingdom since 1997. However, QoI-resistant isolates of Mycosphaerella graminicola were reported for the first time at Rothamsted during the summer of 2002. Sequence analysis of the cytochrome b gene revealed that all resistant isolates carried a mutation resulting in the replacement of glycine by alanine at codon 143 (G143A). Extensive monitoring using real-time polymerase chain reaction (PCR) testing revealed that fungicide treatments based on QoIs rapidly selected for isolates carrying resistant A143 (R) alleles within field populations. This selection is driven mainly by polycyclic dispersal of abundantly produced asexual conidia over short distances. In order to investigate the role of sexually produced airborne ascospores in the further spread of R alleles, a method integrating spore trapping with real-time PCR assays was developed. This method enabled us to both quantify the number of M. graminicola ascospores in air samples as well as estimate the frequency of R alleles in ascospore populations. As expected, most ascospores were produced at the end of the growing season during senescence of the wheat crop. However, a rapid increase in R-allele frequency, from 35 to 80%, was measured immediately in airborne ascospore populations sampled in a wheat plot after the first QoI application at growth stage 32. After the second QoI application, most R-allele frequencies measured for M. graminicola populations present in leaves and aerosols sampled from the treated plot exceeded 90%. Spatial sampling and testing of M. graminicola flag leaf populations derived from ascospores in the surrounding crop showed that ascospores carrying R alleles can spread readily within the crop at distances of up to 85 m. After harvest, fewer ascospores were detected in air samples and the R-allele frequencies measured were influenced by ascospores originating from nearby wheat fields.     

Effects of summer fallow management on take-all of winter wheat caused by <Emphasis Type="Italic">Gaeumannomyces graminis</Emphasis> var. <Emphasis Type="Italic">tritici</Emphasis>

Crop rotation is the oldest, and perhaps the best cultural practice for reducing the risk of take-all. The effects of crops sown before wheat in a rotation are known in detail, but we know little about the opportunities for reducing take-all risk by planting certain crops in the summer period between wheat harvest and the planting of a subsequent winter wheat crop. We investigated the effects on take-all of five summer fallow crops, two soil tillage treatments and a fungicide seed treatment, in a five site-year experiment. We tested the effects of oats, oilseed rape, mustard, ryegrass and volunteer wheat crops. Bare-soil plots were also included. Take-all epidemics varied with year and site. Summer fallow crops had a greater effect on tilled plots. The incidence and severity of take-all were significantly higher in the wheat volunteer plots, whereas maintaining bare soil provided the lowest level of disease. Oilseed rape had no significant effect on take-all incidence in our experiment. The best candidates for reducing take-all risk appeared to be oats, mustard and ryegrass. These summer fallow crops decreased disease levels only when associated with conventional tillage. Summer fallow crops did not alter take-all decline in the same way as a break crop after a wheat monoculture.     

Impact of intraguild predation and lambda-cyhalothrin on predation efficacy of three acarophagous predators

This laboratory study reports the interaction of three predators found in commercial apple orchards in Quebec, Hyaliodes vitripennis (Say) (Hemiptera: Miridae), Harmonia axyridis Pallas (Coleoptera: Coccinellidae) and Amblyseius fallacis (Garman) (Acarina: Phytoseiidae). First, intraguild predation between H vitripennis and the two other predators was characterized in the absence and presence of their extraguild prey, Tetranychus urticae Koch. The results showed an asymmetrical interaction in favour of the larger predator and the levels of intraguild predation were weak for the two predatory combinations. Presence of the phytophagous mite reduced the intensity of intraguild predation in the predatory combination of H axyridis and H vitripennis. Second, the effects of intraguild predation and the application of lambda-cyhalothrin on predation efficacy of the predators were evaluated. The application of the insecticide reduced prey consumption of H vitripennis and H axyridis but did not affect that of A fallacis. Combination of predators and an insecticide application resulted in two different situations depending on the species involved: a reduced predation efficacy for the combination of H vitripennis and H axyridis due to a knockdown effect caused by the insecticide, and no effect on T urticae consumption for H vitripennis and A fallacis. It is suggested that an integrated pest management program based on H vitripennis, A fallacis and lambda-cyhalothrin may be evaluated to repress phytophagous mites in Quebec orchards.     

Isolation of Neospora caninum from the brain of a naturally infected dog, and production of encysted bradyzoites in gerbils

Neospora caninum was isolated from the brain of an adult dog in Brazil. Cerebral tissue from the dog was inoculated into Mongolian gerbils. Gerbils were euthanized 3-4 months later and bradyzoite-containing tissue cysts were observed in their brains. N. caninum (designated NC-Bahia) was isolated in cell culture after inoculation with tissue cysts from the gerbils. The identity of the parasite was confirmed by immunohistochemical examination and polymerase chain reaction (PCR). Gerbils may be a useful alternative to immunosuppressed mice for isolation of N. caninum and for production of encysted bradyzoites.     

Clinical and immunological response of lymphoma dogs following chemotherapy and irradiation

The effect of chemotherapy or chemotherapy followed by total body irradiation and autologous bone marrow transplantation on clinical status and lymphocyte function was evaluated in 79 dogs with spontaneous lymphoma. Advanced disease led to the early deaths of 28 dogs (35%), and 24 dogs (30%) administered chemotherapy had a mean survival time of 85 days (range 33–199 days). Survival for eight dogs receiving chemotherapy and BCG was comparable to that produced by chemotherapy only. Thirteen dogs administered chemotherapy followed by irradiation and autologous marrow grafts had survival times ranging from 59 to > 807 days (median 222 days) with median unmaintained clinical remission lasting 151 days. Most treated dogs experienced improvement in health, reduction in lymph node sizes and normalization of liver function. Lymphocyte reactivity to mitogens and streptolysin-O antigen by untreated and treated lymphoma dogs was depressed (P<0.05) compared to response of normal lymphocytes. Mixed leukocyte reactivity of irradiated lymphoma dogs was impaired in the first 150 days post-irradiation and returned to normal values after 150 days. Lymphocyte responses of irradiated normal dogs paralleled those seen in lymphoma dogs. Mixed leukocyte reactivity was not correlated with tumor rejection since eight of nine dogs evaluated following irradiation relapsed during a period of vigorous reactivity to allogeneic stimulating cells.     

The Cost of Production of Giant Clam Seed Tridacna gigas

The costs of providing giant clam seed in Australia are examined for alternative annual volumes of production. Considerable economies of scale in production are available, both in relation to labor costs and non-labor costs (mostly capital costs). The fall in per-unit cost of producing giant clam seed is considerable when annual production is expanded from 100,000 to 500,000 seed clams per year. At 10% rate of interest, the unit cost per clam seed falls from $1.43–$2.04 at a production level of 100,000 to $0.41–$0.55 at a production level of 500,000. Per-unit operating costs also fall. They decline from $1.01–$1.22 to $0.29–$0.35. This suggests that there are likely to be cost economies in having large centralized hatcheries.     

The use of filter paper discs impregnated with thionin acetate, basic fuchsin and thionin blue in the identification of Brucella species

Filter paper discs impregnated with solutions containing 0.25, 0.5 and 1 mg/milliliter of thionin acetate, 0.75 and 1.5 mg/milliliter of basic fuchsin and 0.5 mg/milliliter of thionin blue were used in the typing of Brucella species. All the strains used reacted as expected, proving this new technique to be reliable in the identification of Brucella species. The method is less expensive and the results easier to interpret than those obtained with methods previously used.