SEED PRODUCTION IN MONOECIOUS AND DIOECIOUS POPULATIONS OF HYDRILLA

The potential for sexual reproduction was evaluated in the various rac es of an international Hydrilla germplasm collection. Crosses between dioecious and monoecious races of Hydrilla verticullata (L.f.) Royle r esulted in seed production in 40 of the 56 crosses (71%). Seeds from 9 0% of these crosses were viable and most seedlings survived. The dioec ious female plant, established in the US since the 1950s, has never be en reported to produce seed, but this female was discovered to be one of the greatest seed producers. This race has been reported to be trip loid, but seed from four of its five crosses were viable. Triploids ar e generally sterile, so these findings raise questions about the repor ted ploidy level of this race. Another observation, not previously rep orted for Hydrilla, was the occurrence of monoecious offspring from di oecious parents. The reported lack of seed production in the US for fe male plants of the dioecious race has been due to the absence of a via ble pollen donor.