by Audrey Verreault | 12 June 2020
Published in Plant Disease 80(5): 494-499
Erwinia carotovora and pectolytic pseudomonads are the most prevalent bacteria associated with soft rot of plants. A procedure based on random amplified polymorphic DNA (RAPD) analysis was developed to distinguish these bacteria rapidly and easily. Forty bacterial strains isolated from diseased plants in the province of Québec were used to screen RAPD primers. Two primers were chosen based on cost considerations and on their capacity to discriminate between the bacterial strains. The combination of the two primers was sufficient for adequate distinction of Erwinia carotovora from pectolytic, fluorescent Pseudomonas spp. Furthermore. E. carotovora subsps. atroseptica and carotovora could also be distinguished from each other. To simplify the identification work, a quantitative identification tool was elaborated, based on selected markers produced with the two primers. To verify the RAPD analysis accuracy, 49 additional soft rot bacteria from diseased plants were submitted to the RAPD procedure and all the identifications were in agreement with those produced by standard biochemical tests. In addition, the RAPD analysis correctly identified 25 bacteria from collections outside of Québec.
by Marie-Claude Boileau | 12 June 2020
Published in Plant, Cell and Environment 19: 949-957
Sudden but transient changes in the fraction of illuminated foliage area in a well-watered 7-year-old Pinus radiata D. Don tree were imposed by completely covering either the upper 22% or the lower 78% of the foliage for periods of up to 36 h. Measurements of transpiration flux density (E), tree conductance (gt), stomatal conductance (gs) and net photosynthesis (A) were made to test the hypothesis that compensatory responses would occur in the remaining illuminated foliage when the cover was installed. When the lower foliage was covered there was an immediate decrease in gt. However, when tree conductance was normalized with respect to the illuminated leaf area (gt‘), it increased between 50 and 75%, depending on the value of air saturation deficit (D). The effect was also apparent from concurrent measurements of increases in gs and A up to 59 and 24%, respectively, for needles in the top third of the crown. When the cover was removed these effects were reversed. The changes in the lower foliage when the upper foliage was covered were much smaller. Changes in bulk needle water potential were small. It is suggested that the observed responses occurred because of a perturbation to the hydraulic pathway in the xylem that could have triggered the action of a chemical signal to regulate stomatal conductance and photosynthesis.
by Audrey Verreault | 12 June 2020
Published in Northern Journal of Applied Forestry 14(3): 117-119
Root suckers arising after cutting 10 yr old pin cherry in eastern Québec were studied. Most suckers emerged during the first 2 yr and only a small proportion emerged after 3 or 4 yr. The number of suckers forming a clone was highly variable and was probably influenced by the degree of interspecific competition affecting this shade-intolerant species. No clonal variations were observed in the diameter of parent roots producing suckers, or in the initiation of new roots around the base of suckers up to 5 yr old. Annual growth of sucker basal diameter differed among clones and also within a clone. The oldest suckers had the greatest rates of basal growth. Results from this study indicate that cutting will not prove effective as a mean for controlling pin cherry during cleaning treatments, but will help to maintain dense pin cherry browse for white-tailed deer or moose.
by Marie-Claude Boileau | 11 June 2020
Published in Canadian Journal of Botany 75: 1424-1435
Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI £ 0.4 and red / far red (R/FR) ratio £ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth.
by Marie-Claude Boileau | 11 June 2020
Published in Plant, Cell and Environment 20: 1462-1472
Experiments were conducted on well watered 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western redcedar (Thuja plicata Donn) seedlings to determine the effects of temperature on whole-plant photosynthetic and stomatal responses to short-term fluctuations in irradiance (Q). Following a step change in Q, time constants (t, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar tA decreased from 30 ± 4 min at 5 °C to 10 ± 1 min at 25 °C. In all cases, tA was within 10-15% of tgs. There was considerable variation in t among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for t accounted for 99% of the diurnal variability in A and gs for seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of daily A were within 2% of those measured. Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3—4 episodes (³ 1 h) of shade (200 or 500 mmol m-2 s-1 or complete darkness during the day. In such cases, daily A was overestimated by up to 4 and 21%, respectively, if a function for t was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in t could lead to increases in daily carbon gains of almost 5% depending on the frequency and degree of shading. If these daily gains were translated into increased dry matter production and compounded, seasonal gains would be even larger.
