Environmental conditions influencing Sclerotinia sclerotiorum infection and disease development in lettuce |
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| Authors: | C S Young † J P Clarkson J A Smith M Watling K Phelps J M Whipps |
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| Institution: | ADAS Consulting Ltd, ADAS Wolverhampton, 'Woodthorne', Wergs Road, Wolverhampton WV6 8TQ;;Horticulture Research International, Wellesbourne, Warwick, CV35 9EF;and;ADAS Consulting Ltd, ADAS Terrington, Terrington-St-Clement, King's Lynn, Norfolk PE34 4PW, UK |
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| Abstract: | The environmental factors that influence infection of lettuce by ascospores of Sclerotinia sclerotiorum , and subsequent disease development, were investigated in controlled environment and field conditions. When lettuce plants were inoculated with a suspension of ascospores in water or with dry ascospores and exposed to a range of wetness durations or relative humidities at different temperatures, all plants developed disease but there was no relationship between leaf wetness duration or humidity and percentage of diseased plants. Ascospores started to germinate on lettuce leaves after 2–4 h of continuous leaf wetness at optimum temperatures of 15–25°C. The rate of development of sclerotinia disease and the final percentage of plants affected after 50 days were greatest at 16–27°C, with disease symptoms first observed 7–9 days after inoculation, and maximum final disease levels of 96%. At lower temperatures, 8–11°C, disease was first observed 20–26 days after inoculation, with maximum final disease levels of 10%. Disease symptoms were always observed first at the stem base. In field-grown lettuce in Norfolk, 2000 and 2001, inoculated with ascospore suspensions, disease occurred only in lettuce planted in May and June, with a range of 20–49% of plants with disease by 8 weeks after inoculation. In naturally infected field-grown lettuce in Cheshire, 2000, disease occurred mainly in lettuce planted throughout May, with a maximum of 31% lettuce diseased within one planting, but subsequent plantings had little (≤ 4%) or no disease. Lack of disease in the later plantings in both Norfolk and Cheshire could not be attributed to differences in weather factors. |
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| Keywords: | ascospores humidity leaf wetness lettuce Sclerotinia sclerotiorum temperature |
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