Electrophoretic Evidence for the Recognition of Two Species in Annual Wild Rice (Zizania, Poaceae)

Abstract

Annual members of the genus Zizania have been classified either as one species, Z. aquatica with five varieties, or as two species: Z. aquatica with three varieties and Z. palustris with two varieties. Electrophoretic divergence among the annual Zizania taxa was examined in 33 pop- ulations collected throughout northeastern North America, including: 11 of var. aquatica, 11 of var. brevis, two of var. subbrevis, three of var. palustris (=var. angustifolia), and six of var. interior, as well as three commercially available cultivars. Eleven enzyme systems presumed to be coded by 17 gene loci were surveyed in 12-24 seedlings of each population. The five varieties divided into two groups on the basis of four enzymes: malate dehydrogenase, hexokinase, phosphoglucose isomerase, and phosphoglucomutase. These corresponded to the two species, Z. aquatica (including vars. aquatica, subbrevis, and brevis) and Z. palustris (including vars. palustris and interior). The five varieties had similar patterns of variation for the other seven enzyme systems. Genetic identity values between Z. aquatica and Z. palustris were similar to levels expected for congeneric species, whereas identity values between varieties within each of the two species and between populations of each variety were similar to those expected for conspecific populations. No isozyme evidence for intermediacy or gene flow between the two species was found. Zizania aquatica varieties could not be distin- guished electrophoretically but small differences were apparent between var. palustris and var. interior in four isozymes. Cultivated varieties, previously considered to be improved strains of Z. palustris var. palustris, were found to be more closely related to Z. palustris var. interior based on the shared presence of unique alleles at six loci.