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Influence of Sclerotinia Wilt on Seed Yield and Quality of Sunflower Wilted at Different Stages of Development¹

Wilt caused by Sclerotinia sclerotiorum (Lib.) de Bary reduced yield and quality of sunflower seeds (Helianthus annuus L.) produced in field plots. The amount of reduction depended upon the stage of plant development when wilt occurred. Less than 0.5% of the plants were wilted at the bud stage and 7.2% by the start of anthesis. Thereafter approximately 6% of the plants wilted each week until 8 weeks after flowering when 60% of the plants had been killed. Seed yields were reduced more than 70% when wilting occurred within 4 weeks of flowering. This reduction was primarily due to lower seed weight. Oil content increased from 32.7% for plants wilted in the first 2 weeks, to 46.4% when wilting was delayed until 8 weeks after flowering. Protein content of oil-free meal was fairly stable and averaged 53.1% during the first 5 weeks, but increased to 57.7% thereafter. Fatty acid composition was relatively unaffected by wilting as linoleic acid content varied from 74.4 to 76.8%. Thus, the oil was considered to be of excellent quality regardless of when wilting occurred.

Key Words: Sclerotinia sclerotiorum • Helianthus annuus • Yield loss • Oil content • Protein content • Fatty acid composition

² Head, Crop Science Section, and research scientist, respectively, Agriculture Canada, Research Station, Morden, Manitoba, R0G 1J0.

Received for publication July 6, 1978.