Comparative Studies of Monoecious and Dioecious Hydrilla (Hydrilla verticillata) Biotypes

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Abstract
Selected biological and physiological parameters of hydrilla [Hydrilla verticillata(L.f.) Royle # HYLLI] biotypes were compared in growth chambers, glasshouse, or outside aquaria. Salinity tolerance was similar for both biotypes with an injury threshold of approximately 13 parts per thousand (ppt). The registered aquatic herbicides diquat (6,7-dihydrodipyrido [1,2-α:2′,1′-c] pyrazinediium ion) and dipotassium and monoamine salts of endothall (7-oxabicyclo [2.2.1] heptane-2,3-dicarboxylic acid)4produced similar injury to both biotypes. Biomass of the monoecious plants, growing in controlled environments, declined under short days. Tuber production in monoecious plants was greatest under short days and was significantly higher than in dioecious plants under the same conditions. Growth response to temperature was similar among all plants and was retarded at 15 C. Tuber germination occurred at lower temperatures in the monoecious plants, which was indicative of a lower temperature tolerance. Vegetative propagules were the only perennating structures observed in the monoecious biotype, and regrowth was entirely from tubers and turions. The annual growth habit, in conjunction with rapid and abundant propagule production, adapts the monoecious biotype to northern areas with short growing seasons.