Peter V. Blenis

Effects of burial, stem portion and cultivar on the decomposition of canola straw

Buried canola straw underwent 1.6 to 2 times as much decomposition as straw on the soil surface. Decomposition of Brassica napus L. was slightly less than that of B. rapa L. and cultivar effects were small in one year and insignificant in the other. Because treatment effects varied between stems and roots, plant portion likely should be considered in decomposition studies. Key words: canola, straw decomposition, burial, cultivars

Clone by isolate interaction in the hybrid poplar-Septoria musiva pathosystem

Fourteen clones of hybrid poplar were inoculated with 19 isolates of Septoria musiva Peck under greenhouse conditions to determine the magnitude of the clone, isolate, and clone × isolate interaction effects. Septoria musiva isolates were collected from five geographic areas, two symptoms (canker and leaf spot), and two host types (native species and hybrid poplar). The hybrid poplar clones were classified by parent type (Populus deltoides Bartr. ex Marsh., Populus laurifolia Lebed. × Populus nigra L., and P. deltoides × (P. laurifolia × P. nigra)). There were no significant differences among geographic areas (p = 0.443), symptoms (p = 0.842), or hosts (p = 0.304) of origin for the 19 isolates nor significant differences among the three parent types (p = 0.089). Clone, isolate, and clone × isolate interaction effects were all significant, accounting for 65%, 15%, and 18%, respectively, of the explained variation. These results indicate that clones rather than parent types should be the focus of resistance...

A Method to Induce Stem Cankers by Inoculating Nonwounded Populus Clones with Septoria musiva Spore Suspensions

Most artificial inoculations of Populus spp. stems with Septoria musiva have required host wounding to induce canker development; in the absence of wounds, frequencies of cankers have been low. Three greenhouse inoculation experiments were conducted to demonstrate the reliability and repeatability of an inoculation method that did not require wounding. In the first, 16 clones of hybrid poplar were inoculated with three isolates of S. musiva to compare responses following wounding and inoculation with mycelium (wound inoculation) with responses following inoculation of nonwounded trees by spraying with a conidial suspension (spray inoculation). Stem disease severity among clones following spray inoculation was correlated with stem disease severity following wound inoculation. A significant clone-isolate interaction was detected with spray inoculation but not wound inoculation. In the other two greenhouse experiments, 29 clones of hybrid poplar and 69 clones of Populus balsamifera were inoculated with a spore suspension mixture of three isolates. In both cases, the experimental error was similar to that obtained in previous experiments, in which trees were wound inoculated, and was adequately small to permit detection of differences in responses among clones. Ultimately, field studies will be needed to determine the best inoculation method for predicting stem responses to this pathogen under field conditions. However, relative to wound inoculation, spray inoculation of nonwounded trees has the advantage of yielding faster results, permitting inoculation with a mixture of isolates, and not circumventing potential mechanisms for resisting penetration. The ability to infect stems without wounding creates opportunities for numerous types of epidemiological and disease control studies that are difficult to conduct with wound inoculation.

Herbage yield and crude protein concentration of rangeland and pasture following hog manure application in southeastern Alberta

Intensive hog production is expanding into semi-arid regions of Alberta, where perennial forage lands are increasingly targeted for manure applicati on despite limited guidelines for its efficient use. Herbage yield and crude protein were assessed over two consecutive years within two native rangelands and two tame pastures, following different rates (10, 20, 40, 80 and 160 kg ha-1 NH4-N), methods (surface banding vs. subsurface injection) and seasons (fall vs. spring) of one-time liquid hog manure (LHM) application. Increasing manure rates improved grass yield across all sites the first growing season after treatment, from 1626 to 3576 kg ha-1. Although absolute increases in production were greatest on tame pasture, relative yield increases were similar among sites. Average crude protein (CP) concentration also increased from 69 to 91 g kg-1 in the first year. Despite low rainfall and the absence of a yield response in the second year, grass CP and crude protein yield (CPY) were maximized with increased ...

Evaluating fungi from wood and canola for their ability to decompose canola stubble

The survival and impact on canola of Leptosphaeria maculans, the causal agent of blackleg, might be reduced by agents that decompose canola stubble. Fifty-six fungal isolates from wood or canola were evaluated for their ability to overcome several biological and (or) physical constraints to their effectiveness in decomposing and (or) eliminating L. maculans from canola stubble. Relative to fungi from canola, wood decay fungi were more tolerant of reduced water potential but somewhat less tolerant of lower temperature. Wood decay fungi were no better than those isolated from canola at decomposing sterile canola stubble and less able than Coprinus spp. and Cyathus olla in colonizing and surviving in nonsterile stubble. None of the isolates were effective in eliminating L. maculans from stubble pieces or causing significant decomposition of nonsterile stubble either under laboratory conditions or in the field. These results suggest that considerable effort would be required to find isolates effective in managing blackleg disease through stubble decomposition. Wood decay fungi would seem to have little potential as biological control agents in this pathosystem because of their inability to colonize and decompose nonsterile canola stubble.

Effects of Spore Availability, Spore Germinability, and Shoot Susceptibility on Gall Rust Infection of Pine

Temporal changes in three factors (shoot susceptibility, spore availability, and spore germinability) were evaluated to estimate their effects on the infection of lodgepole pine (Pinus contorta var. latifolia) by Endocronartium harknessii. Germinability of rust spores from sori free of hyperparasites remained above 80% during the growing season and thus would not have significantly limited infection. In contrast, there was a slight, but statistically insignificant, increase in estimated susceptibility as infection increased from 94% of maximum at 45% shoot elongation to maximum susceptibility at 90% shoot elongation. This was followed by a precipitous decline in estimated susceptibility to 57% of maximum when shoots were 95% elongated. Spore availability was 24% of maximum when shoots were 45% elongated, and thus may have been limiting at the beginning of the growing season. At the end of the growing season, spore availability declined prior to, or simultaneous with, the decline in susceptibility. The combined effect of both factors drastically reduced the number of infections estimated to occur once shoots are more than 95% elongated. As shoots elongated, relatively more infections formed higher on the shoot, supporting the hypothesis that periderm is important in limiting infection.

Seasonal Variation in Resistance of Aspen Stems to Shearing Force

Abstract Seasonal changes in aspen (Populus tremuloides Michx.) resistance to shearing force were described to determine their apparent contribution to seasonal changes in cattle utilization. Shearing resistance of current-year, 1-year-old, and 2-year-old stem-age classes were measured from late spring to early fall. For all stem-age classes, resistance to shearing force increased with time, partially due to increasing stem diameter. Depending on stem-age class, resistance to shearing force increased by 200%–2000% between the first and last measurements of a given year. Increased resistance of aspen stems to shearing force in late summer may reduce their selection by cattle. Grazing management that defers cattle entry until midsummer could reduce damage to regenerating aspen associated with cattle foraging in cut blocks.

Inoculation of Populus tremuloides with Pollaccia americana

Disease resistance may represent the best approach for controlling shoot blight, caused by Pollaccia americana Ondrej, in aspen (Populus tremuloides Michx.) plantations. Experiments were conducted to develop methods for screening for resistance under greenhouse conditions. Chickpea agar supported abundant inoculum production. An inoculum concentration of 5 × 104 spores/mL and a seedling age of 5-9 weeks were appropriate for evaluating infection. Infection severity was not correlated with tree height or leaf number. Differences in infection among clones varied with fungal isolate. The number of isolates and replicates needed to detect resistance differences among clones was calculated using estimated values of experimental error and clone × isolate interactions.

Temporal occurrence and impact of Scytalidium uredinicola, a mycoparasite of western gall rust

Scytalidium uredinicola Kuhlman et al. is considered an important mycoparasite of western gall rust caused by Endocronartium harknessii (J.P. Moore) Y. Hiratsuka (= Peridermium harknessii J.P. Moore). The temporal occurrence of S. uredinicola and its impact on the ability of western gall rust spores to germinate were determined. Scytalidium uredinicola was not isolated from either external or internal tissues of 3- to 5-year-old galls at any time of the year. However, it was isolated from the external, but not internal, tissues of 6- to 9-year-old galls in most months and from both external and internal tissues of 10+-year-old galls in all months. On galls older than 10 years, S. uredinicola overwintered beneath the periderm and colonized developing rust sori prior to peridial rupture in April. Spore viability of western gall rust was consistently reduced by 85% throughout the period of sporulation over two sporulating seasons. Because S. uredinicola requires considerable time to become persistent and perennial, artificial establishment of the hyperparasite in the early stages of gall rust epidemics might be required to make it an effective biological control agent.

Whole-tree water relations of western gall rust infected lodgepole pine trees.

Lodgepole pine (Pinus contorta Dougl. ex Loud.) trees having galls resulting from infection by western gall rust (WGR; Endocronartium harknessii (J.P. Moore) Y. Hiratsuka) have a lower ability to conduct water than nongalled stems. Experiments were conducted to compare the leaf-specific hydraulic capacity (Q L; g H2O·cm−1 ·MPa−1) of galled and control trees. Specific objectives were to test the hypothesis that Q L was reduced in galled trees, to determine which components of Q L, if any, varied between galled and control trees, and to test the hypothesis that water stress would more negatively affect galled trees than control trees. Under well-watered conditions, galled trees had lower Q L than control trees. This difference was associated with an increased water potential difference between the soil and leaves (ΔΨ MPa) rather than a change in transpiration per unit leaf area (E L; g H2O·cm−2 A L). Although water stress reduced Q L, the effect was similar for galled and control trees, indicating that the former were no more vulnerable to xylem cavitation than the latter. The similarities in the short-term responses of galled and control trees under well-watered conditions are consistent with the observation that stem galls do not result in rapid tree mortality.