Symptom Variability and Selection for Reduced Severity of Cotton Seedling Disease Caused byPythium ultimum

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Abstract
Hypocotyls of seedlings of cotton cultivars Auburn M. Coker 310, Delcot 277J and Dixie King 3 were inoculated with P. ultimum. Selected plants were grown to maturity and self-pollinated; progenies were evaluated for disease severity. Variation in hypocotyl symptom expression among seedlings within cultivars did not differ among the 4 cultivars. Variation in symptom expression among seedlings of ''Auburn M'' was not reduced significantly among progenes through 3 successive generations of selection and self-pollination. A small but significant difference in susceptibility to P. ultimum between ''Delcot 277J'' and ''Coker 310'' was established. This difference was apparent in the parent seedlings and in 2 succeeding generations of selection and self-pollination of resistant plants. Reduced disease severity was demonstrated in progenies of ''Auburn M''. Third-generation seedlings of ''Auburn M'' were significantly more resistant than the cultivar parent.