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Distribution and Analysis of Isozyme Polymorphism in North American Cultivated Oat Germplasm

Agric. Sci. Ctr.-North, N222K, Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-00914
Dep. of Crop Science, North Carolina State University, Raleigh, NC 27695-7629

^* Corresponding author.

This study was conducted to analyze the extent and distribution of isozymic variation among 405 accessions of fall- and spring-sown North American oat (Avena sativa L. and A. byzantina K. Koch) cultivars, introductions, and germplasm releases. Each accession was screened for variation at 29 enzyme zones. An initial classification of cultivars was based upon date of introduction or release, and by fall vs. spring season of production. Spring and fall germplasm pools were separated on the basis of frequency differences for isozyme genotypes present in both germplasms rather than genotypes unique to either pool. Fall germplasm appeared more genetically diverse due to its greater numbers and percentage of genotypes present at intermediate frequencies. A second analysis based upon Jaccard's distances between all pairwise combinations of the 405 accessions revealed 16 clusters containing nine or more accessions. Nine clusters were predominantly spring germplasm, four were predominantly fall germplasm, and three were comprised of a mixture of both. Thus, a continuum in cluster composition was observed when no a priori categorization of cultivars by season of production was imposed. Nine spring, fall, and mixed germplasm clusters containing many spring and fall introductions and cultivars of the pre-1940 era grouped in the center of a three-dimensional principal component plot. Post-1940 spring accessions formed two clusters on either side of this older germplasm. Based upon isozymic diversity, the fall- and spring-sown North American germplasm pools probably represent different ecotypes of a single species.

Received for publication April 30, 1992.