Evaluation of Amaranthus Accessions for Resistance to Damping-Off by Pythium myriotylum. Ramsey L. Sealy, Graduate Research Assistant, Department of Horticultural Sciences, Texas A&M University, College Station 77843. C. M. Kenerley, and E. L. McWilliams. Assistant Professor, Department of Plant Pathology and Microbiology, and Professor, Department of Horticultural Sciences, Texas A&M University, College Station 77843. Plant Dis. 72:985-989. Accepted for publication 26 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0985.

One hundred twenty-six accessions of species and cultivars of Amaranthus were screened for resistance to damping-off by Pythium myriotylum. Accessions ranged in resistance from very susceptible (> 100% weighted mortality) in a vegetable cultivar of A. tricolor from India to very resistant (1.8% weighted mortality) in A. tricolor ‘Early Splendor’. Both cultivars and wild species included susceptible and resistant groups. Cluster analysis was used in an attempt to place the accessions into resistance clusters. However, examination of the resulting dendrogram and the results of a ranking procedure indicated that few, if any, natural clusters exist in these data. It was suggested that accessions that exhibited weighted percent mortalities of less than 20% be selected for use in breeding programs to breed in resistance to damping-off by P. myriotylum. Promising accessions for breeding programs included 13 cultivars of A. tricolor, four cultivars of A. dubius, a cultivar of A. hybridus, an accession of A. spinosus, and an accession of A. palmeri.