Potato tissue resistance to the growth of Phytophthora infestans (Mont.) de Bary

Kassim, Mohammed Yahia Ahmed (1976) Potato tissue resistance to the growth of Phytophthora infestans (Mont.) de Bary. PhD thesis, University of Glasgow.

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This thesis describes an investigation of aspects of race nonspecific resistance which determines the rate at which tuber tissue is colonized by Phytophthora infestans. It was mainly concerned to deterimine whether active resistance mechanisms are involved or whether resistance could be explained by passive factors only. Five clones with different levels of race non-specific resistanc were used. Hyphal growth rates in all clones and in all tissues tested were similar and thus growth rate can play no part in the differences in race non-specific resistance between these clones. The growth rates in all experiments at all temperatures used were linear indicating that resistance does not involve active factors accumulating in the tissue ahead of the lesion to concentrations high enough to affect hyphal growth. Thus resistance to hyphal growth would appear to depend upon passive factors only. The growth rate on different media was always faster than that in tuber tissue indicating that hyphal growth in vivo may be affected by inhibitory factors, but if so, these factors are equally active in all clones. The total time required for the penetration and initiation of hyphal growth at the inoculated surface and for the establishment of visible sporulating mycelium on the opposite surface (Growth phases I and III) differed between clones and thus is a factor in the differences in race non-specific resistance 'between the clones. The rate of initiation and spread of lesions in the tubers differed between clones. These rates, in all clones, were slower than those calculated for the initiation of hyphal growth and for hyphal growth itself, indicating that the hyphae are growing ahead of the fluorescent tissue surrounding the nectoric tissue. The tuber tissues of the different clones were colonized to an equal extent and thus there was no evidence to indicate that active factors might accumulate to different levels in the tissues behind the hyphal front in the different clones and thus affect the extent to which lateral branches developed to further colonize the tissues. Hyphae were distributed non-randomly in the medullary tissue in the tubers and stems of Craigs Alliance and in the tubers of Pentland Dell and Pentland Squire, indicating that this tissue is not uniformly susceptible to colonization, but that there are pockets of tissue more resistant than others. Four types of haustoria were found in tuber and stem tissue but only two types were found in leaf tissue and there was no obvious relation between haustorial type and resistance. Haustoria were distributed non-randomly between cells indicating that cells may differ in their resistance to penetration. There were also differences between clones in total number of haustoria produced which appeared to be correlated with resistance to growth phases I and III and to resistance to lesion growth. Thus factors affecting haustorial formation may be important in the differences in race non-specific resistance between the clones.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D D Clarke
Keywords: Plant pathology
Date of Award: 1976
Depositing User: Enlighten Team
Unique ID: glathesis:1976-72074
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 13:07
Last Modified: 17 May 2019 13:07
URI: https://theses.gla.ac.uk/id/eprint/72074

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