Pathogenicity of A and B morphotypes of Sphaeropsis sapinea confirmed on American larch (tamarack) and European larch

Fungi identified as Sphaeropsis sapinea (or synonyms) have been reported from Larix. Lack of pathogenicity tests, confusion about the identity of isolates mentioned in previous literature, and existence of distinct populations (A and B morphotypes) of the pathogen indicated the need to evaluate the ability of S. sapinea to cause disease of larch. Elongating snoot tips of Larix decidua, Larix laricina, and known hosts of the pathogen, Pinus banksiana and Pinus resinosa, were inoculated with water-agar plugs colonized with an A or a B isolate, or sterile plugs (controls). Each of five replications included five seedlings for each treatment-species combination. After 6 weeks, no symptoms had developed on control seedlings, but two-way analyses of variance revealed significant effects of isolate morpnotype and host on both incidence and severity of disease (values of p ≤ 0.01). The A isolate killed almost all shoot tips, but the B isolate killed from no P. resinosa shoots to 56% of L. laricina shoots. The average length of shoot killed by the A isolate was also greater than that killed by the B isolate. Response to the B isolate again varied among species, with greater average lengths of shoot killed on the larches (compared with the pines). Both A and B morphotypes of 5. sapinea should be considered among the fungi encountered on L. decidua and L. laricina.     

Hymenoscyphus fraxineus can directly infect intact current‐year shoots of Fraxinus excelsior and artificially exposed leaf scars

Hymenoscyphus fraxineus, the causal agent of ash dieback, was inoculated onto intact, unwounded current‐year shoots and leaf scars of 4‐year‐old, potted Fraxinus excelsior seedlings. Pieces of ash wood colonized by the fungus were used as inoculum. Three of 25 (12%) of the inoculated intact shoots and nine of 25 (36%) of the inoculated leaf scars were infected by H. fraxineus and developed typical symptoms of ash dieback, including necrotic lesions on the shoot surface and wood discoloration as well as shoot and leaf wilting distal to the inoculation site. No symptoms occurred on control seedlings, which had been inoculated in the same way but with sterile wood pieces. Visible necrotic lesions on shoots and wood discoloration were statistically significantly longer in proximal than in distal direction from the inoculation site, a pattern which resembles symptoms after natural infection. The ash dieback pathogen was re‐isolated from nine of 12 (75%) of the symptomatic seedlings. These results provide indirect supportive evidence that the fungus infects shoots via leaves and shows that it is able, under experimental conditions using a massive mycelial inoculum, to directly infect intact, unwounded current‐year shoots of its main host in Europe.     

Blight of conifer seedlings caused by Colletotrichum gloeosporioides

In a growth chamber experiment, 70-day-old seedlings of 10 conifer species were inoculated with Colletotrichum gloeosporioides conidia to determine the host range of the fungus. Based on the percentage of seedlings affected and the disease severity on individual seedlings, the order of most to least susceptibility was: western hemlock (WH), mountain hemlock, western larch, Sitka spruce, Engelmann spruce, Douglas-fir (coastal form, then interior form), white spruce and ponderosa pine; lodgepole pine and western red cedar remained unaffected. Inoculation of WH needles showed that within 24 h C. gloeosporioides conidia germinate and appressoria (penetration structures) form. A growth chamber study demonstrated that the pathogen can infect WH at needle wetness periods as short as 15 min; number of needles affected was higher at 0.5 h, but did not increase further even when wetness was extended up to 8 h. The results are discussed in relation to blight management of greenhouse-grown conifer seedlings.Portion of a Bachelor of Science (Honors) thesis, Department of Biology, University of Victoria, Victoria, British Columbia.     

Site preference and occurrence patterns of <Emphasis Type="Italic">Picea jezoensis</Emphasis> and <Emphasis Type="Italic">Abies sachalinensis</Emphasis> on decayed logs in natural coniferous forests in Hokkaido,northern Japan

The objectives of this study were to investigate differences in the site preferences of seedlings of Picea jezoensis and Abies sachalinensis on decayed logs, and to examine the occurrence patterns of seedlings and saplings of the two species and whether they occur together or separately on logs. We characterized the habitats of 1–2-year-old seedlings of the two species on logs and examined the relationship of the two species on logs by growth stages in two plots. One plot had been disturbed about 50 years ago whereas the other had not for a long time. Although the thickness of moss and the litter layer in the habitats of 1–2-year-old seedlings were significantly different between the two species, the two species could occur together. In one study plot, seedlings and saplings of the two species occurred together. The initial occurrence pattern of the seedlings affected the occurrence patterns of the saplings on logs. The occurrence patterns of the seedlings and saplings of the two species on logs seemed to be affected by the abundance of seed trees. In the other study plot saplings of the two species occurred separately, but one species was not always competitively superior to the other species. Disturbance history affected the occurrence patterns of the saplings of the two species on decayed logs at the two study plots. Consequently, it is concluded that seed dispersal and the abundance of available logs, which are usually affected by disturbance, are significant factors in the natural regeneration of conifers in Hokkaido.     

The effects of early and intense pruning on light penetration,tree growth,and epicormic shoot dynamics in a young hybrid larch stand

We examined the effect of early and intense pruning on light intensity under the canopy, individual growth, diameter–height relationships, and epicormic shoot dynamics in young hybrid larch (Larix gmelinii var. japonica × L. kaempferi) to establish a new effective management method for hybrid larch plantations. The objective is to produce high-quality wood while reducing silviculture costs using a combination of low-density planting and early and intense pruning. In a young hybrid larch plantation, we pruned branches to two different heights (2 and 4 m above ground level) using a no-pruning treatment as a control. Although the growth rates were lower in the heavy pruning treatment (4 m above the ground level) than in other treatments in the year following pruning, when measured 4 years later, growth did not differ between treatments. The number of epicormic shoots increased in the year following pruning, as did the relative photosynthetic photon flux density (rPPFD). The number of epicormic shoots was also dependent on the size of individual trees. However, survival of epicormic shoots was not sufficiently high to be problematic for high-quality timber production. If branches are pruned carefully such that the rPPFD does not rise above 20%, the emergence of epicormic shoots can also be controlled. Our results indicate that early and intense pruning is an effective component of a new management system for hybrid larch plantations.     

Eight-year performance of bareroot Douglas-fir and bareroot and plug western larch Seedlings following herbicide applications,northeast Oregon,USA

Plantation success in northeastern Oregon can be limited by poor survival for western larch (Larix occidentalis Nutt.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco) seedlings. Vegetation management treatments may increase soil moisture availability during the dry summer months, thereby increasing the probability of seedling survival. Chemical site preparation treatments were applied in spring 2007, summer 2007, and spring 2008 to determine if such treatments would improve survival and growth of bareroot Douglas-fir and bareroot and plug western larch seedlings on three sites near Elgin, Oregon. Although some herbicide treatments significantly increased survival, results were not consistent among sites. Overall, Douglas-fir had greater survival after 7–8 years than larch seedlings. Seedling size 7–8 years after planting was also highly variable among sites and treatments with larch seedlings being taller and larger than Douglas-fir seedlings, on the average. Size for all stock types was negatively correlated with vegetative cover and positively correlated with first-year soil moisture. Macro- and microclimatic conditions, including topography and soil depth, were likely contributors to differences in survival and growth.     

Early infection by Heterobasidion annosum in Larix x eurolepis seedlings planted on infested sites

The incidence of Heterobasidion annosum was examined in three young hybrid larch (Larix × eurolepis) plantations in southern Sweden that were established after felling Norway spruce (Picea abies) stands heavily infected by the fungus. The incidence of H. annosum was 7 %, 33 %, and 70 %, respectively, in the 2-, 3-, and 5-year-old plantations. In all plantations, H. annosum was the most frequent rot-causing fungus (81 %) and all isolates tested belonged to the P-intersterility group. No visible external differences between infected and healthy seedlings were found on any site. Both tap and lateral roots were infected by H. annosum. The results suggest that when hybrid larch is planted on sandy soils after clear felling of Norway spruce heavily infected by H. annosum, it is very susceptible to infection by H. annosum. Furthermore, transfer of H. annosum from infected stumps to hybrid larch occurs during the first few years after planting on scarified sites. In this study, scarification may have exacerbated the root disease situation and actually led to more early infections by distributing pieces inoculum across the sites.     

Allocation of 14C-carbon in two species of larch seedlings infected with ectomycorrhizal fungi

The flow of labeled carbon in ectomycorrhizal and non-ectomycorrhizal seedlings of Japanese larch (Larix kaempferi Sarg.) and its F1 hybrid (Larix gmelinii Rupr. x L. kaempferi) was studied. Larch seedlings were grown in a greenhouse for 110 days with larch forest soil (FM) or Suillus grevillei (SM) inoculum, or in the absence of ectomycorrhizal fungi (NM). Shoots of colonized and NM seedlings were exposed to a pulse of 14CO2 for 1 h under natural light. Seedlings were harvested following 0, 6 and 24 h of exposure to 14CO2. At the final harvest, SM seedlings of Japanese larch and hybrid larch allocated 2.6 and 2.5% more 14C, respectively, to roots than NM seedlings. In contrast, FM seedlings of Japanese larch and hybrid larch allocated 6.5 and 18.0% more 14C, respectively, to the stem than NM seedlings. Of the total 14C detected in needle, stem and root fractions, FM and SM seedlings allocated a greater proportion than NM seedlings, perhaps because FM and SM seedlings had significantly (P < 0.05) higher photosynthetic rates than NM seedlings. As a result, FM and SM seedlings had greater dry masses than NM seedlings. Concentrations of nitrogen and phosphorus in FM and SM seedlings were significantly (P < 0.05) higher than in NM seedlings, as was stomatal conductance.     

Dry mass production in seedlings of Norway spruce infected by the needle rust Chrysomyxa rhododendri

The aim of this study was to assess the losses in productivity of Norway spruce (Picea abies) due to the attack by Chrysomyxa rhododendri, a rust that only penetrates new developing flushes. Three-year-old seedlings were artificially infected once or twice in two consecutive years and the dry mass was determined at the end of the growing season. Dry mass accumulation of all parts including roots was significantly reduced if more than about one-third of the young foliage was infected. Shoot and root dry mass of once severely infected seedlings were 32 and 48% less than that of controls. This deficit could not be compensated during a following rust-free year. When seedlings were infected in two consecutive years, dry mass accumulation was reduced by 58% compared with controls. Results indicate that rejuvenation of and afforestation with Norway spruce can seriously be impaired by Chrysomyxa at the alpine timberline where Rhododendron sp. (the telial host of the parasite) is widespread.     

Growth and branching habit of rooted cuttings collected from epicormic shoots of Betula pendula Roth

Patterns of shoot growth and branching were studied over two growing seasons in rooted cuttings collected from both epicormic shoots and seedlings of Betula pendula Roth. Epicormic shoots were induced to sprout on stumps and small logs of 5-, 10- and 30-year-old trees. The use of epicormic shoots enhanced the rooting capacity of stem cuttings collected from these shoots but did not appear to reverse the process of maturation. In this study, maturation was based on characteristics typical of mature trees but not necessarily those of the mother plant, because it was not possible to root cuttings, for comparison, from 5-, 10- and 30-year-old ortets, other than from epicormic shoots. There was evidence of the persistence of mature characteristics through an increase in shoot plagiotropism with increasing ortet age. Rooted cuttings from both seedlings and epicormic shoots, however, assumed an increasingly orthotropic habit with a smaller shoot angle at the end of the first growing season than at the beginning and this continued into the second growing season. Other indications of maturation, such as delayed bud flushing and the incidence of flowering with increasing ortet age, were also evident in rooted cuttings from epicormic shoots. There was a clear difference in branching habit depending on cutting source. Rooted cuttings derived from epicormic shoots produced nearly twice as many lateral branches compared with rooted cuttings collected from seedlings, but this was not an effect of maturation. There was some evidence that rooted cuttings derived from seedlings grew taller than rooted cuttings from epicormic shoots.