Cutting clear

The short stories in this collection explore the effects of having belonged to the Canadian subculture of treeplanters. Most of the main characters are ex-treeplanters: young, or to their dismay, not so young, middle class women and men who have experienced hard, seasonal labour in the Canadian wilderness. They may have taken up planting in the first place as a means to pay for university or travelling, or to support their music or art, but most of them returned to it year after year, finding in it something more compelling than just the money. Now, they have quit, or are on the brink of quitting planting, in some cases due to the physical injuries caused by the job. They are trying to get a life outside of planting but are crippled by their connections to their past planting experiences. The protagonists' attempts to grapple with these connections--connections which take the form of relationships, fears (of bears or nine-to-five jobs), environmental or class awareness--are often ambiguous or ineffective. But by the end of the stories their view of planting, whether utopic or dystopic has been tested. They are forced to see how their view affects the people around them and the choices, or lack of choice, it provides

Mechanisms of biological control of crown and root rot in tomato by a nonpathogenic Fusarium oxysporum strain

The biological control of crown and root rot in tomato was studied in a sterile system in which tomato seedlings were grown on water agar in petri plates or on filter wicks in test tubes containing fertilizer solution. The biological control agent, nitBl, was a nonpathogenic strain of Fusarium oxysporum which had been mutated to a nitrate non-utilizing form in order to distinguish it from the pathogen, Fusarium oxysporum f. sp.radicis-lycopersici (FORL). Four different approaches were used to deduce possible mechanisms of control. One approach was to study the effect of inoculum timing and inoculum density on biological control. Biological control was demonstrated when nit B1 was inoculated to the roots as much as 21 days before FORL, and persisted for at least 23 days after the FORL inoculation. When nit B1 was inoculated to seedling roots at least 3 days before FORL, there was good disease control even when the initial inoculum density of nit B1 was 60 times lower than that of FORL. As the lag between inoculations decreased, higher densities of nit B1 were needed to bring about control, and when the two fungi were inoculated simultaneously the inoculum density of nit B1 had to be at least 10 times that of FORL for there to be any reduction of disease symptoms. The second approach was to observe the colonization of seedling roots by the two strains. Both nit B1 and FORL colonized the outer layers of the root. However, when nit B1 was inoculated to the root 4 days before FORL, the rate of increase of nit B1 was greater than the rate of increase of FORL. The third approach was to test possible elicitors of a defence reaction in tomato for their biological control ability. Sterile filtrates from cultures of nit B1 grown in nutrient broth, sterile exudates from nit B1-infested germinating seeds and seedling roots, heat-killed nit B1 spores, and the cell wall fraction from nit B1 all failed to protect seedlings against crown and root rot induced by FORL. The fourth approach was to test nutrient competition by adding an excess of nutrients that might otherwise be limiting. Biological control by nit B1 was not affected when excess glucose or iron were added to the growth medium. In a related experiment, FORL caused severe disease symptoms (in the absence of nit B1) even when iron availability was artificially decreased by adding a strong iron chelator to the growth medium. The conclusion from all these experiments was that nit B1may elicit a defense response in tomato roots, possibly dependent on the prior colonization of the roots by this strain, which makes the roots resistant to subsequent infection by FORL.Land and Food Systems, Faculty ofGraduat

Native pollinators alone provide full pollination on small-scale commercial cranberry (Ericaceae) farms

AbstractCranberry (Vaccinium macrocarponAiton (Ericaceae)) requires insect pollen vectors to maximise fruit yield. In many areas, commercial producers use managed bees (Hymenoptera: Apidae) to supplement native pollinators. On the island of Newfoundland, Newfoundland and Labrador, Canada, due to the small number of available honey bee hives and import restrictions on commercially reared bumble bees, the use of supplemental pollinators is rare. Four farms were studied for two years to identify key pollinators and determine the relationship between fruit yield and bee abundance. The most commonly collected bees were species ofBombusLatreille (Hymenoptera: Apidae), which buzz-pollinate and are likely the primary pollinator on these farms; thus, fruit yield was examined with respect to totalBombusabundance. Stigma loading was also used as a measure of pollinator effectiveness. Contrary to expectation, there was no relationship betweenBombusabundance or stigma loading and either fruit set or weight, but there was significant year-to-year variation. Other factors were likely more important in determining yield, and further research is needed to identify those. Under current conditions, native bees provide ample pollination services for maximal yield.</jats:p

Intraguild interactions and large-scale population patterns

Competitive interactions, including interference and intraguild predation, occur in many aquatic food webs and influence large-scale patterns of abundance, especially in lentic habitats. In a study of small coastal streams in eastern Canada, we found patterns suggesting that abundances of a predatory invertebrate, Sweltsa onkos (Plecoptera:Chloroperlidae), are influenced by another predator, Rhyacophila vibox (Trichoptera:Rhyacophilidae). Larval densities of the 2 species were inversely correlated, and mortality of larval S. onkos tended to be higher in streams with many R. vibox. Abundance and mortality of a 3(rd) predatory species, Isoperla montana (Plecoptera:Perlodidae), were unrelated to abundances of the other species. Laboratory behavioral observations confirmed that interactions between R. vibox and S. onkos were asymmetrical; high densities of R. vibox led to higher injury and mortality rates and lower growth rates of S. onkos, whereas S. onkos had no effect on R. vibox growth or mortality. Previous work has shown that R. vibox reaches high densities only in streams with few or no fish, and we conclude that the relative abundances of S. onkos and R. vibox in the study streams might be influenced by differences in Vulnerability to intraguild and fish predation