Volume

37, 1999

Issue

1

Page

17

Title

High-temperature effects on growth and propagule formation in hydrilla biotypes

Author(s)

McFarland, D.G., and J.W. Barko

Abstract

 In consecutive greenhouse studies, growth and propagule formation were examined first in monoecious hydrilla [Hydrilla verticillata (L.f.) Royle], then in dioecious hydrilla, at three temperature levels (25, 30, and 35 C) and contrasted over three periods of growth (8, 12 and 16 wks). Each biotype was grown under natural photoperiods, decreasing from 14 hrs (in Aug) over 8, 12, and 16 wks respectively to 12, 11, and 10 hrs (in Oct, Nov, and Dec). For both biotypes, total biomass and root-to-shoot ratios were significantly reduced at 35 C; greater biomass was produced both at 25 and 30 C. Increases in growth period generally enhanced total biomass and shoot production; however, shoot length was unresponsive to growth periods beyond 8 wks. The 35 C treatment strongly impeded tuber formation and eliminated the production of axillary turions; the number and biomass of these propagules peaked at lower temperatures under short photoperiods after 12 to 16 wks. Shoot elongation was stimulated with increases in temperature and was especially pronounced in the dioecious biotype. Notably, in the monoecious biotype, the number of shoots as a potential source of fragments, and tuber production (although reduced) occurred at relatively high levels under unfavorably high-temperature (35 C) conditions. These results suggest that monoecious hydrilla may be better adapted to high temperatures than previously shown, and that the distribution of both biotypes in the US could overlap further in southern states.

Key words: Hydrilla verticillata, biomass, morphology, tubers, turions, reproduction, thermal conditions, photoperiod