Influence of photoperiod on vegetative propagule production in three turion-producing races of Hydrilla verticillata (L.f.) Royle

Three races of hydrilla observed to only produce turions were evaluated for photoperiod effects on propagule production. Greatest production was under shortdays (I 0-h). These races from Japan and Poland produced both turions and turion-like tubers under longday photoperiods (I 6-h) but production was most efficient under shortdays. Increased propagule production under shortdays may be compensation for decreasing photosynthetic activity at higher latitudes. Production appears only to be limited by temperature.