Disease resistance in the Senecio vulgaris L./ Erysiphe fischeri Blumer wild plant pathosystem

Bevan, Josette R (1986) Disease resistance in the Senecio vulgaris L./ Erysiphe fischeri Blumer wild plant pathosystem. PhD thesis, University of Glasgow.

Abstract

An investigation was made of the frequency and distribution of race specific resistance in two populations of groundsel (Senecio vulgaris) to the powdery mildew fungus Erysiphe fischeri. Ten different powdery mildew isolates were tested on a sample of 98 plants from Glasgow and 151 from the National Vegetable Research Station (NVRS), Wellesbourne. Five of the isolates were collected at Glasgow and 5 from NVRS Additional plants were assessed using only 5 isolates from Glasgow. In total, 247 plants from Glasgow and 266 from NVRS were assessed. Plants were tested with several isolates at a time by using detached leaves on benzimidazole supplemented agar. Generally the frequency of plants detected with race specific resistance to each isolate v/as low, ranging from 1% to 10%. However, the frequency of resistant plants in the NVRS population to one isolate from Glasgow, G9, was relatively high, at 35%. The majority of these plants originated from a small, intensively sampled plot of 17 m by 17 m. The frequency of resistance to the remaining 9 isolates was low and of a similar order in both groundsel populations. However, the tendency for more plants to have resistance at NVRS was significant. Ten different resistance phenotypes were detected in groundsel plants from Glasgow, and 24 from NVRS, 9 of which were common to both populations and included the phenotype susceptible to all isolates. This indicates that patterns of race specific resistance were essentially similar in each population, but there was greater variation at NVRS Partial resistance was more common at NVRS and natural frequencies of mildew infection were lower at NVRS, possibly, the defence strategy was more effective here than at Glasgow. The groundsel population was highly heterogeneous, 10 resistance phenotypes were detected, using 5 mildew isolates, in 75 plants from a 1 m by 1 m plot. This heterogeneity was reflected in the mildew population. Of 24 isolates characterized on 50 inbred groundsel lines, 18 were found to be different. a minimum of 14 avirulence genes could explain the observed reactions of the 18 races. The races were complex, having several virulence genes and usually only one avirulence gene, but races with up to 5 avirulence genes were also detected. Studies of partial resistance began to reveal the complexity of the defence strategy deployed by groundsel. Partial resistance was very common in groundsel and could be race specific in some instances whilst non race-specific in others. Some individuals possessed both complete and partial resistance. Perhaps crop plant breeding programmes should aim to include both forms of resistance within a cultivar. Plant age had a significant effect on all forms of resistance. Incubation temperatures could alter the susceptibility of some plant lines to sane isolates. The effects of plant age and temperature could be considered race specific in nature, since sane plant lines switched from susceptible to resistant under one set of conditions to a particular isolate, whilst under another set of conditions, and with another isolate, resistance switched to susceptibility. An investigation of sporeling development, revealed that Erysiphe fischeri conidia commonly form several germ tubes on susceptible host tissue. Each germ tube has the potential to form an appressorium and initiate infection. Resistance was expressed at the haustorial and secondary hyphal stages of development.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Botany, Plant pathology
• Date of Award: 1986
• Depositing User: Enlighten Team
• Unique ID: glathesis:1986-76618
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 14:02
• Last Modified: 19 Nov 2019 14:02
• URI: https://theses.gla.ac.uk/id/eprint/76618