Journal of the American Society for Horticultural Science (1993)
MALE AND FEMALE FERTILITY OF LOOSESTRIFE (Lythrum) CULTIVARS
Neil O. Anderson and Peter D. Ascher
Department of Horticultural Science, University of Minnesota
1970 Folwell Avenue
St. Paul, MN 55108
ABSTRACT
Recent legislative efforts in Minnesota and other states restricting the sale and cultivation as a noxious weed, purple loosestrife (L. salicaria, L. virgatum, and their cultivars), has brought the issue of cultivar fertility to the forefront of discussion between the nursery industry, gardeners, and environmentalists. Cultivars have been assumed to be sterile and it has been argued that they should not be included in this legislation. Male and female fertility, seed germination, and progeny fertility were used to determine cultivar fertility. One short- , 11 mid-, and six long-styled cultivars were included in this study. Duplicates of several cultivars from different nurseries and three unknown cultivars from Minnesota gardens were also collected. Plants from 17 Minnesota and one Wisconsin population of L. salicaria served as fertile male and/or female testers. Pollen stainabilty (usually 100%) showed high levels of male gamete viability. Pollen size within anther type varied widely; 2n gametes were present in primarily the short and mid anther morphs. Seed production per capsule from legitimate cross-pollinations, using cultivars as male parents with Minnesota or Wisconsin female testers, averaged 47.8 + 36.1 across style morphs. Cultivars were significantly different as males (F=3.4, P=0.0002) as were anther morphs (F=10.2, P<0.00001). With female fertility tests, seed set per capsule ranged from zero to 152 and averaged 53.5 + 39.7. Seed set for other crosses showed similar trends. only 'Morden Gleam' produced no seed with all legitimate pollinations, although illegitimate selfs or interspecific crosses produced seed. L. salicaria x cultivar legitimate crossing groups had 30 - 100% germination. Common male and female parents within each legitimate crossing group were not significantly different (F=0.51, P=0.477). This study showed that the cultivars are highly fertile when used as male or female parents with wild purple loosestrife, native species (L. alatum), or other cultivars. Thus, cultivars grown in gardens could serve as pollen or seed sources for the continued spread of purple loosestrife. The implications of cultivar fertility, especially interspecific F1 hybrids, is discussed in relation to the spread of noxious weeds in wetlands.
M. Sc. Thesis, September 1991
THE DISTRIBUTION, REPRODUCTIVE BIOLOGY, AND MORPHOLOGY OF Lythrum SPECIES, HYBRIDS, AND CULTIVARS IN MANITOBA
Kimberly Alexandra Ottenbreit
Faculty of Graduate Studies
University of Manitoba
Winnipeg, MB
ABSTRACT
Lythrum salicaria L. (purple loosestrife) is a rapidly spreading, naturalized perennial herb of moist habitats and is considered detrimental to wetland productivity in North America. The first herbarium record for Manitoba was collected from Neepawa in 1896. As of 1991, 38 sites in Manitoba from field work, correspondence and herbarium records were identified. Most of these were in the watersheds of the Red and Assiniboine Rivers. Dispersal is mostly by means of seed. Significantly more seed matures in the capsules in the lower and mid regions of the infructescence compared to those from the top. Seed is shaken by wind from the capsules between late summer and the end of winter. Germinability of seed from 28 cultivated and naturalized populations averaged 92 percent, however cultivars had low seed production (especially 'Morden Pink'). Discriminant analyses identified calyx pubescence, calyx lobe length, and calyx appendage length as significantly reliable features for separation of cultivars from naturalized plants. The cultivars 'Morden Pink', 'Dropmore Purple', and 'Morden Gleam' were self-incompatible, but artificial crosses between these and a naturalized population when legitimate were for the most part fertile. Resulting seeds averaged 98 percent germination and the hybrid plants were highly interfertile. Thirty-seven percent of the hybrid progeny were classified in discriminant analysis as being indistinguishable from a naturalized population which grows on the Assiniboine River. Controlling the spread of L. salicaria will be accomplished by preventing seed production in naturalized populations, and by removing cultivars from locations where they may affect pollen transfer with naturalized populations.
Abstract from K. Ottenbreit thesis for Master of Science, Faculty of Graduate Studies, the University of Manitoba, Winnipeg, Manitoba, September 1991, 145 pp.
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