No description available.

The thesis is presented in two parts. PART I. A study of Cucurbitaria piceae Borthwick, a disease of the buds of the Spruce. PART II. A study of Pseudopeziza ribis Kleb. (Gloeosporiura ribis (Lib.) Mont. and Desm.), the Leaf Spot disease of the black currant. The work which forms the basis for Part I was carried out at the Department of Botany of the University of Edinburgh prior to September 1952. It was continued, under leave of absence, together with the work described in Part II, at the Department of Agriculture and Horticulture of the University of Bristol.

The principal aim of the study was to further the knowledge of the interaction between Alternaria linicola and the host plant linseed (Linum usitatissimum). A novel detached cotyledon in vitro bioassay was developed to allow the quantification of disease resistance of Linum material to A. linicola. Differences were apparent between the disease response scores of four linseed varieties when tested with seven isolates of the pathogen which differed in aggressiveness. However, there was no significant difference between the disease response scores of the varieties and no change in the ranking of varieties over three experiments. This indicated that the varieties behaved in a predictable manner to each isolate during each test. Accordingly, in a subsequent study, 102 Linum accessions were challenged with an aggressive and a non-aggressive isolate. About 75 % of the accessions gave a moderate response, although there was a continuous distribution of resistance from high susceptibility to resistant. Accessions at both extremes of the disease response consisted of breeding material, currently grown varieties and near relatives of the host species. For example, one of the more resistant accessions tested was Linum angustifolium. A sub-set of nine Linum accessions was chosen (a range of susceptible, moderately-resistant and resistant material) and the resistance response of the material to an aggressive and a non-aggressive A. linicola isolate was investigated using a whole seedling inoculation technique. A comparison of the response of the material during the seedling test with that of the detached in vitro assay indicated that the latter test systematically, but marginally, overestimated the disease response. The in vitro bioassay scores and the seedling test scores were positively correlated following inoculation with the more aggressive of the two isolates. It was suggested that the resistance response of material could be accurately predicted by the in vitro bioassay but that a certain level of isolate aggressiveness was necessary to differentiate between responses of the accessions. Since large isolate-line interactions with respect to resistance scores were not observed, the results implied that resistance was polygenically determined. These results indicate that the bioassay for disease resistance produces an accurate measure of resistance and provides plant breeders with a useful tool which can be utilised during breeding programs.

No description available.

Comparisons were made between the sensitivities of unique ‘wild’ isolates and domestic isolates of the dry rot fungus, <i>Serpula lacrymans</i>, to temperature, water potential and pH. Comparisons were also made between their capacities of timber decay. The ‘wild’ Himalayan isolates displayed slightly less marked sensitivities to high and low temperature and lowered water potential, yet the isolates were equally tolerant of pH. In general, the linear growth rates of the domestic isolates proved to be twice those of the ‘wild’ Himalayan set, whereas little variation occurred between their rates of timber decay. This study also resulted in the first isolation and reliable identification of ‘wild-growing’ <i>S. lacrymans</i> collected in Europe. The main part of the project involved the construction of novel chambers in order to examine the effects of lowered humidity and moving air flow on the activity of <i>S. lacrymans</i>. In the smallest and simplest of these, its growth and timberdecaying activities could be stopped by incubation at 86% relative humidity or by the application of a pumped air flow rate of 2.5 litres per minute; however, <i>S. lacrymans</i> was not inactivated until more-stressful conditions were applied. In addition, an intermediate rate of air flow provoked marked directional growth away from the stress. Furthermore, the introduction of stone, brick and plaster into these models encouraged the capacities of timber decay and mycelial growth. The use of a larger and more representative model incorporating simulated flooring and plaster walling within glass tanks revealed differences in the appearances and patterns of colonisation by <i>S. lacrymans</i> depending upon whether aged or new materials were used. Treatments involving air drying by fans caused both a shrivelling and a loss of viability of the fungus only when there was no ‘reservoir’ of water available; when there was water present, latent activity remained. An elaboration of this experimental design tested the effects of a combined biological and environmental treatment. Subsequently, the application of <i>Trichoderma harzianum</i>, a known antagonist of <i>S. lacrymans</i>, proved not to be an effective remedial treatment on its own, but appeared to impart a mildly protective effect when combined with a drying regime. Importantly, in the latter situation <i>T. harzianum</i> caused a severe degradation of the part of the colony responsible for the uptake of water in <i>S. lacrymans</i>. Another workshop-scale model simulating more authentically a damp sub-floor space and a cavity behind aged plaster walling was developed. When respective treatments by fan drying and passive ventilation were compared, the former were more effective, but its efficacy could be augmented by incorporating low-level passive ventilation via discreet vents. In this manner, a successful remedial treatment of <i>S. lacrymans</i> could be effected, though the prevalence of mould could prove to be undesirable in practice. However, some samples of this displayed antagonistic effects against <i>S. lacrymans</i>. A further experiment was designed to test the effects of air drying on the production of the stress-protective carbohydrate trehalose and of some associated solutes by <i>S. lacrymans</i>. In contrast to reports of some other organisms, no definite stockpiling of any of the compounds occurred. A final series of experiments revealed that <i>S. lacrymans</i> removed calcium, silicon and iron from sandstone and calcium, sulphur and iron from aged plaster; these elements were sequestered on its hyphae, especially in the form of calcium oxalate. Degradation of the sandstone was implicit but not obvious microscopically. Furthermore, <i>S. lacrymans</i> transported iron from these building materials through its mycelial system. An attempt to determine the effects of separate minerals in sandstone and plaster on timber decay revealed few variations.

No description available.