Leaf extracts of 500 plants from 47 guayule (Parthenium argentatum Gray) entries including AZ-101, Gila, Cal-3, Cal-6, and Cal-7 germplasms; 12 accessions from Mexico; and a diverse array of diploid, triploid, and tetraploid selections were analyzed for isozyme variation of 17 enzyme systems. Glutamate oxalacetate transaminase (GOT, EC 184.108.40.206), isocitrate dehydrogenase (IDH, EC 220.127.116.11), malate dehydrogenase (MDH, EC 18.104.22.168), phosphoglucoisomerase (PGI, EC 22.214.171.124), shikimate dehydrogenase (SKDH, EC 126.96.36.199), and triosephosphate isomerase (TPI, EC 188.8.131.52) produced sharp and well-resolved bands. With the exception of AZ-101 and Gila, intra- and inter-accession polymorphisms were present for the above enzymes. Plants of AZ-101 and Gila showed identical banding patterns for every enzyme, supporting the view that these two germplasms may be the apomictic progenies of a single selection. Isozyme variations within entries indicated that most of the available guayule germplasms and selections are heterogeneous. Differences between entries suggested that isozymes may provide useful markers for cultivar identification.
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