Shoot dieback of lodgepole pine in the British Isles has been a long standing problem, but it was not known whether or not a pathogen was involved. During 1980--1982, a shoot dieback disease of lodgepole, similar to those previously observed at different places, was studied at the Glengarry and Eilanreach forests in the northwest of Scotland. Dieback symptoms and stages in their development were investigated. A thorough review of the literature on dieback disease of lodgepole pine indicated that different disease symptoms were involved in the present outbreaks. A hitherto undescribed fungus, Ramichloridium pini de Hoog & Rahman was found to be closely associated with the early stages of discolouration of the buds and shoots of lodgepole pine while Sclerophoma pythiophila (Cda.) Hohn was most prevalent on healthy and dead tissues. A new modified Czapek Dox Agar medium has been found to suppress S. pythiophila significantly while allowing normal growth of R. pini at about 15°C, which is the optimum temperature for the latter. A method of mass production of inoculum was devised. For germination of the conidia of R. pini free water is not essential. Good germination of conidia and elongation of germ tubes occurred on undetached flushing needle sheaths and bud scales. Extensive artificial inoculations have firmly established that R. pini is the primary pathogen of the present shoot dieback disease of lodgepole pine. Most successful infections were obtained from inoculations carried out in May and June. By October, shoots became resistant to infection. Plants of the Central Nass River provenance were more resistant to R. pini than those from Long Beach, Washington. It has been shown that conidia produced on needle fascicle scars could provide natural inoculum. The infection period lay between mid April to mid May or up to early June at Eilanreach in 1981.

The objectives of the project were to develop an understanding of the disease dynamics caused by Phytophthora citricola in native plant communities in the south of Western Australia. Prior to 1983, the pathogen had only been reported twice from Australian forests. Since then, P. citricola has been extensively recorded from plant communities north and south of Perth, and is currently the second most frequently recovered Phytophthora species from the northern jarrah forest and the northern sandplains. The objectives were addressed by examining the biology, ecology and taxonomy of isolates of P. citricola local to the southwest. Examination of the intraspecific variation of P. citricola by isozyme analysis resolved three major electrophoretic subgroups (SG), and these were aligned with morphological and cultural variation within the species. One electrophoretic SG was confined to forested areas. This SG differed from other SGs in sporangial dimensions, growth rate on two media and in vitro sensitivity to phosphonate. A redescription of the species may be warranted. P. citricola was positively associated with two roads in the northern jarrah forest. Road surfaces were sampled, then soil overburden was removed and the surface of the concreted lateritic layer beneath was sampled. Isolation of P. citricola declined away from the road into the adjacent forest and was more frequently recovered from the caprock (up to 1 metre below soil surface) than from the soil surface. The most probable source of introduction was from infested soil on vehicles using the roads. Oospores were shown to be produced in two soils, a lateritic gravelly loam and sand, and in plants. In soil, the electrophoretic SG confined to the forest (loamy soil) produced only limited numbers of oospores in the sandy soil of the northern sandplain. The restriction of this SG to the forested areas is probably physiological, rather than limited dispersal, with the SG currently occupying the full extent of its range. Estimation of the relative persistence of oospores, zoospores and plant material colonised by P. citricola established that only oospores (either free in soil or in colonised plant material) were important in long tern survival in soil. Oospores were still viable after six months at two field sites, and after 18 months in soil in the laboratory. Phosphonate is currently the most promising method of control of Phytophthora induced disease in native plant cornmunites of the southwest. The efficacy of phosphonate against P. citricola was examined in vivo and in vitro against two SGs. Phosphonate successfully inhibited lesion growth of both SGs in vivo, but of only one electrophoretic subgroup in vitro. The ecological implications of infestation of native plant communities in the southwest of Australia are discussed.

Thesis (Ph. D.)--Murdoch University, 1996. / Thesis submitted to the School of Biological and Environmental Sciences. Includes bibliographical references (leaves 134-153).

Thesis (Ph.D.)--Murdoch University, 2003. / Thesis submitted to the Division of Science. Bibliography: leaves 151-176.

Frost damage to sapling size plantation Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco.] in the central interior of B.C. was identified as the major cause of dieback and canker through tree dissections. Prominent frost rings in the wood and frost damage to buds and shoots corresponded to the dates of dieback initiation and canker events throughout the history of the plantations. Frost rings and frost cankers were reproducible using an artificial freezing technique. Symptomatic frost-damaged buds and elongating shoots were described for Douglas-fir, white spruce [Picea glauca (Moench) Voss] and subalpine fir [Abies lasiocarpa (Hook.) Nutt.]. The effect of growing season frost was most noticeable on early flushing trees. Frost and dieback damage was most severe on concave and flat landforms, which are conducive to cold air pooling on nights with strong radiative cooling. Several pathogens isolated from recently killed stems were identified from fruiting bodies and culture. Leucocytospora kunzei (Sacc.) Urban was the pathogen most commonly isolated from the edge of expanding cankers and progressive dieback margins. Sclerophoma semenospora Funk was commonly found fruiting on dead stems and leaders killed by frost or by mechanical means. Cinara pseudotaxifoliae Wilson feeding caused latent cankers on one year old leaders of Douglas-fir, which are thought to be activated by frost. Boron levels of both healthy and severely affected trees were in the intermediate range, and were not considered to play an important role in frost or pathogen susceptibility for Douglas-fir in the interior. / Forestry, Faculty of / Graduate

European ash trees (Fraxinus excelsior ) are under threat from the fungal pathogen Hy- menoscyphus fraxineus causing ash dieback disease (ADB). Previous research has shown heritable variation in ADB susceptibility in natural ash populations. Prior to this project, very little genetic data were available for ash, thus hampering efforts to identify markers associated with susceptibility. In this thesis, I have presented nuclear and organellar assemblies of the 880 Mbp F. excelsior genome, with a combined N50 scaffold size of over 100 kbp. Using Ks distributions for six plant species, I found evidence for two whole genome duplication (WGD) events in the history of the ash lineage, one potentially shared with olive (Ks 0.4), and one potentially with other members of the Lamiales order (Ks 0.7). Using a further 38 genome sequences from trees originating throughout Europe, I found little evidence of any population structure throughout the European range of F.excelsior, but nd a substantial decrease in effective population size, both in the distant (from 10 mya) and recent past. Linkage disequilibrium is low at small distances between loci, with an r2 of 0.15 at a few hundred bp, but decays slowly from this point. From whole genome DNA methylation data of twenty F. excelsior and F. mandshurica trees, I identi ed 665 Differ- entially Methylated Regions (DMRs) between those with high and low ADB susceptibility. Of genes putatively duplicated in historical WGD events, an average of 25.9% were differen- tially methylated in at least one cytosine context, possibly indicative of unequal silencing. Finally, I found some variability in methylation patterns among clonal replicates (Pearson's correlation coefficient 0.960), but this was less than the variability found between different genotypes ( 0.955). The results from this project and the genome sequence especially, will be valuable to researchers aiming to breed or select ash trees with low susceptibility to ADB.

No description available.

No description available.

Lic.-avh. Uppsala : Sveriges lantbruksuniv. / Härtill 2 uppsatser.

A Cytospora species isolated from infected tissues and sporulating stromata on diseased trees caused typical dieback symptoms when inoculated into Prunus species and was identified as the primary cause of stonefruit dieback in the Okanagan. Based on the morphology of the stromata, spore dimensions, and colony growth and color on malt extract agar, the fungus was identified as C. leucostoma (Sacc). After including the number of trees removed during the winter of 1985-86 and 1986-87 because of Cytospora sp., an average of 14.8% of the trees in 17 stonefruit orchards were affected by dieback from September 1985 to September 1987. The incidence of Cytospora sp. in the individual blocks ranged from 3.0-56.9%. In 11 of the 17 orchards surveyed in 1986 and resurveyed in 1987, dieback symptoms were evident on trees which had been symptomless in 1986. The percent of newly infected trees in these 11 blocks ranged from 0.4-8.8% and averaged 2.9%. The majority of sporulating Cytospora sp. infections were found on the scaffold limbs (69%) or trunks (28%) of infected trees. Pruning wounds (65%), rather than winter injury (25%), were the major infection courts. Fall and spring inoculations of a spore suspension (10³ spores/ml) of either a peach isolate (P8-19) to peach, or a cherry isolate (C9-23) to cherry revealed that intraspecies spread of the disease can occur at any time of the year. Although spring spore inoculations of the peach isolate to cherry or the cherry isolate to peach resulted in significantly (P = 0.05) more infections than the control treatments, identical fall inoculations did not. This suggests that spread of Cytospora sp. between cherry and peach is most likely to occur in the spring. The effect of temperature on spore germination and mycelial growth of Cytospora sp. in vitro was isolate-dependent. The minimum lag period for Cytospora sp. spore germination occurred at 27° C. Spores germinated at temperatures as low as 10° C, and remained viable even after exposure to -18° C for 1 week. The temperature optima for the in vitro growth of most stonefruit isolates in this study was 20-23° C. Viable Cytospora sp. spores were washed from infected trees (10⁵-10⁶ spores/ml) and adjacent healthy trees (10⁴ spores/ml) in mid-December and collected in funnel traps after the first rain the following spring (late April). Under Okanagan conditions, infection of fresh pruning wounds made in the spring can occur either by spores which overwintered on infected trees and were dispersed by spring rains, or by spores dispersed by fall rains to healthy trees on which they overwintered and infected following pruning. Benomyl (1 g a.i./L), dichlone (1 g a.i./L), flusilazole (0.01 g a.i./L) and ziram (5 g a.i./L) applied as water sprays did not significantly (P = 0.1) reduce the percent infection compared to the unprotected, inoculated controls. Of eight fungicide-pruning paste mixtures, only benomyl added to either Heal 'n' Seal or linseed oil significantly (P = 0.1) reduced the number of cankers which developed compared to the untreated control. / Land and Food Systems, Faculty of / Graduate