SHORT-DAY EXPOSURE PERIOD FOR SUBTERRANEAN TURION FORMATION IN DIOECIOUS HYDRILLA

Two experiments conducted in the greenhouse determined that a minimum of 20 short-days (SD) were required for induction of hydrilla [Hydrill a verticillata (L.f.) Royle] subterranean turions. Fertilizer was appl ied to the plants in one study but not the other There were 15 treatme nts ranging from 0 to 60 sequential days under SD conditions. Measured parameters included shoot weight, subterranean turion number and weig ht. The unfertilized plants began producing subterranean turions only after exposure to 20 SD, while in the other study, the fertilized plan ts produced subterranean turions only after being exposed to 38 SD. Th e shoot weight of the unfertilized plants decreased with increasing SD exposure; whereas that of the fertilized plants increased. The weight of subterranean turions produced did not significantly differ between the two studies. The unfertilized plants produced 0.17 subterranean t urions per day after induction while the fertilized plants produced 0. 89 per day.