MALE AND FEMALE FERTILITY OF LOOSESTRIFE (LYTHRUM) CULTIVARS

Male and female fertility, seed germination, and progeny fertility wer e used to determine cultivar fertility in species of Lythrum. One shor t-, 11 mid-, and six long-styled cultivars were included in this study . Duplicates of several cultivars from different nurseries and three u nknown cultivars from Minnesota gardens were also collected. Plants fr om 17 Minnesota and one Wisconsin population of L. salicaria served as fertile male and/or female testers. Pollen stainability (usually 100% ) showed low levels of male gamete abortion. Pollen size within and am ong anther type varied widely; possible 2n gametes were present in pri marily the short- and mid-anther morphs, Seed production per capsule f rom legitimate cross-pollinations, using cultivars as male parents wit h Minnesota or Wisconsin female testers, averaged 48 +/- 36 across sty le morphs. Cultivars differed as males, as did anther morphs. With fem ale fertility tests, seed set per capsule ranged from zero to 152 and averaged 54 +/- 40 in legitimate pollinations (i.e., pollinations betw een stamen and styles of the same length). Seed set for other crosses showed similar trends. Only 'Morden Gleam' produced no seed with all l egitimate pollinations, although illegitimate selfs or interspecific c rosses produced seed. Seed from legitimate crosses of L. salicaria x c ultivars had 30% to 100% germination. Common male and female parents w ithin each legitimate crossing group were not significantly different. This study showed that the cultivars are highly fertile when used as male or female parents with wild purple loosestrife, native species (L . alatum Pursh.), or other cultivars. Thus, cultivars grown in gardens could serve as pollen or seed sources for the continued spread of pur ple loosestrife. The implications of cultivar fertility, especially in terspecific F-1 hybrids, is discussed in relation to the spread of nox ious weeds in wetlands.