An Investigation of Factors Influencing the Incidence of Potato Tuber Blight Caused by Phytophthora infestans (Mont.) De Bary

Fairclough, Robert William (1995) An Investigation of Factors Influencing the Incidence of Potato Tuber Blight Caused by Phytophthora infestans (Mont.) De Bary. PhD thesis, University of Glasgow.

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This study investigated the factors that affect the incidence of tuber blight, with particular reference to the occurrence of tuber blight in the absence of any visible foliar blight. The factors investigated were fungicide type, the severity of stem blight, edaphic factors, particularly soil moisture and the production of P. infestans inoculum on daughter and seed tubers. In addition, the infection of tubers during washing for the pre-pack market and its control were also studied. The results in this thesis have demonstrated that foliar lesions are not the only source of P. infestans inoculum for the infection of daughter tubers. It was demonstrated that lesions on the stem base are an important source of sporangia and that in certain circumstances inoculum produced on infected seed or daughter tubers may also infect healthy daughter tubers directly. These less obvious sources of inoculum could explain the occurrence of high incidences of tuber blight in the absence of visible foliar lesions. In a field experiment fungicide type affected the date on which incidences of tuber blight significantly greater than zero first occurred, the date on which the maximum amount of tuber blight occurred and the overall incidence of tuber blight. The effect of fungicide type on the relationships between foliar blight and the overall incidence or timing of tuber infection was modest. Fungicide type did, however, substantially affect the severity of stem blight at which incidences of tuber infection significantly greater than zero occurred. The severity of stem blight varied more with fungicide type than did the percentage foliar blight. In field and laboratory experiments the growth rate of P. infestans in leaflets was influenced by fungicide type and some fungicides resulted in significantly reduced incidences of subsequent petiole and stem infection. In contrast, when the stems were inoculated directly, fungicide type had little effect on stem lesion development. The use of ELISA to monitor the growth of P. infestans in inoculated stems of plants in a growth cabinet showed that stem lesions continued to develop in conditions that were not suitable for the production of abundant sporangia. In this experiment the number of sporangia produced on stem lesions, after incubation of the stems in a high humidity, did not increase substantially until the rate of lesion growth declined. Sporangia production was more closely related to the length of the lesion supporting sporulation than the lesion length per se. In glasshouse and field experiments incidences of tuber blight significantly greater than zero occurred following the irrigation of plants whose main stem had been inoculated with P. infestans but whose foliage was maintained fi-ee of blight. Another field experiment demonstrated that the incidence of tuber blight was significantly correlated with the length of stem lesions but not with the percentage of foliar blight. Soil moisture content greatly influenced the incidence and development of blight on daughter tubers. Increasing the soil moisture content of field plots to 75% of field capacity for approximately 12 weeks significantly increased the spread of P. infestans from inoculated daughter tubers to other tubers on the same plant. Healthy tubers on the same plant that were 5 cm fi-om the source of inoculum became infected when the soil moisture content was this high. Tubers on bait plants that were up to 60 cm away fi-om the nearest plant with an inoculated tuber were also infected. In laboratory studies increasing the soil moisture content to 79% of field capacity pre-inoculation increased the proportion of inoculated daughter tubers which became infected whereas soil moistures above 39 % of field capacity post-inoculation reduced infection. However, post-inoculation soil moisture contents up to 79% of field capacity considerably increased the development of lesions and sporangia production on infected daughter tubers. Soil temperature had less of an effect on infection, lesion development and inoculum production. Increasing the soil moisture content above 79% of field capacity immediately following inoculation decreased the infection of seed tubers inoculated 6 months after harvest. Inoculum production on the infected seed tubers increased with soil moisture content up to 79% of field capacity although there was little effect of moisture content on lesion development. When seed tubers that had been inoculated soon after harvest were planted the following year in soil with moisture contents below 79% of field capacity they remained sound for a period of 58 days. A soil moisture of 79% of field capacity increased the number of tubers supporting sporulation by P. infestans. The transfer of tubers, that were not supporting sporulation after 58 days, from soils at 39% or 59% of field capacity into soil at 79% of field capacity resulted in the production of viable sporangia on these tubers 7 days after transfer.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Ruairidh A Bain
Keywords: Plant sciences, Plant pathology
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-74758
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Nov 2019 15:58
Last Modified: 13 Nov 2019 15:58

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