Expression of defensive genes from a promoter that is specifically activated in response to pathogen invasion is highly desirable for engineering disease-resistant plants. A plant transformation vector was constructed with transcriptional fusion between the pathogenresponsive win3.12T promoter from poplar and the gene encoding the novel cecropin A-melittin hybrid peptide (CEMA) with strong antimicrobial activity. This promoter-transgene combination was evaluated in transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) for enhanced plant resistance against a highly virulent pathogenic fungus Fusarium solani. Transgene expression in leaves was strongly increased after fungal infection or mechanical wounding, and the accumulation of CEMA transcripts was found to be systemic and positively correlated with the number of transgene insertions. A simple and efficient in vitro regeneration bioassay for preliminary screening of transgenic lines against pathogenic fungi was developed. CEMA had strong antifungal activity in vitro, inhibiting conidia germination at concentrations that were non-toxic to tobacco protoplasts. Most importantly, the expression level of the CEMA peptide in vivo, regulated by the win3.12T promoter, was sufficient to confer resistance against F. solani in transgenic tobacco. The antifungal resistance of plants with high CEMA expression was strong and reproducible. In addition, leaf tissue extracts from transgenic plants significantly reduced the number of fungal colonies arising from germinated conidia. Accumulation of CEMA peptide in transgenic tobacco had no deleterious effect on plant growth and development. This is the first report showing the application of a heterologous pathogen-inducible promoter to direct the expression of an antimicrobial peptide in plants, and the feasibility of this approach to provide disease resistance in tobacco and, possibly, other crops.

Two stunt nematode species, Geocenamus brevidens and Quinisulcius capitatus , were recovered from the potato growing regions of southern Alberta, described and characterized based on integrative taxonomy. Morphometrics, distribution, and host associations of both species are discussed. The Canadian populations of both species displayed minor variations in morphometrical characteristics (viz., slightly longer bodies and tails) from the original descriptions. The populations of G. brevidens and Q. capitatus species examined in this study are proposed as standard and reference populations for each respective species until topotype specimens become available and molecularly characterized. Phylogenetic analyses, based on partial 18S, 28S, and ITS sequences, placed both species with related stunt nematode species. The present study updates the taxonomic records of G. brevidens and Q. capitatus from a new location, southern Alberta, Canada, and will aid in the decision whether these stunt nematodes should be included in nematode management programs.

Many economically important species of Populus, especially those in sections Aigeiros and Tacamahaca, remain recalcitrant to genetic transformation. In this study, a simple and reliable protocol was developed for the efficient Agrobacterium-mediated transformation of a difficult-to-transform, but commercially viable, hybrid poplar Populus nigra L. x P. maximowiczii A. Henry (NM6). A plant transformation vector designed to express the beta-glucuronidase (GUS) gene was used to detect transformation events at early stages of plant regeneration and to optimize parameters affecting poplar transformation. The use of zeatin riboside in shoot-induction medium, regeneration of shoots via indirect organogenesis, and early selection pressure were the major modifications that drastically improved the efficiency of poplar transformation and minimized the number of untransformed regenerants. Transgenic shoots were routinely obtained 4-10 weeks after co-culture with A. tumefaciens, with a greater than 90% rate of plant recovery. Stable transgene integration, ranging from a single insertion to ten copies per genome, was confirmed by Southern blot analysis. The mean transformation frequency was 36.3% and about two-thirds of the lines had 1-2 transgene copies. Among the explants, petioles and leaves had a higher transformation frequency than did stem segments. Growth characteristics and the morphology of transgenic poplar plants were identical to untransformed controls. These findings will accelerate the development of P. nigra x P. maximowiczii plants with novel traits, and may also be useful to improve transformation procedures for other Populus species.

Pin nematodes (Paratylenchus spp.) are polyphagous parasitic species with a wide host range and geographical distribution; their diversity is unknown in the potato growing region of Alberta, Canada. The present study aims to provide morphological and molecular characterization of three pin nematode species, namely P. neoprojectus, P. tateae, and a new species, Paratylenchus enigmaticus sp. nov. All of them were recovered from the potato growing region of southern Alberta. The nematodes were isolated using the sieving and flotation-centrifugation method, and their morphology was assessed by light microscopy. Molecular characterization was performed using partial 18S, D2–D3 expansion domains of the 28S and ITS ribosomal genes. This study is the first report of molecular characterization of P. tateae and P. neoprojectus, being new records from southern Alberta, and two Spanish populations of P. tateae comprising the first report of this species in Europe. The phylogenetic analysis of the 18S, D2–D3 expansion domains of the 28S and ITS ribosomal DNA regions underscores the importance of using molecular data for accurate species identification and clarifies the status of P. nanus type B and P. sheri. Moreover, our findings will be useful to determine the impact of pin nematodes on potato production in future field research.

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