Time from flowering to seed viability in purple loosestrife (Lythrum salicaria)

L. salicaria is a troublesome invasive species in eastern North America. Control methods being considered include use of herbicides, phytophagous insects and cutting. More effective use of these methods, separately or as an integrated program, requires better knowledge of seed viability for this plant which is a prolific seed producer. Infloresences of L. salicaria were collected from an infestation over one growing season. Ten inflorescences were collected on each sampling date; five of which were examined while they were fresh and five were allowed to desiccate in a greenhouse under ambiant conditions. Germination tests were performed on seeds from both fresh and dried inflorescences. From 12 days after anthesis (DAA) up to and including 24 DAA, there were no seeds that were germinable on either the fresh or dried inflorescences. At 27 DAA, germinable seed was first found in the lower 20 nodes of the freshly cut inflorescences. Above node 20, the inflorescence was in bloom but the seed capsules were immature. From 27 DAA on, percent germination from most of the nodes up the stem increased with time. This same pattern was observed in the seeds from the dried inflorescences. Germinable seed was first detected 27 DAA on the dried inflorescences in the lower 10 nodes. As the inflorescences expanded, the upper nodes matured and germination was not significantly different between the fresh and dried inflorescences. Desiccation of the cut stems of L. salicaria did not affect the germinability of the seeds. There was no evidence of further maturation and greater seed viability on the dried stems as compared to the germinability of seeds from freshly cut stems. This indicates that cutting or chemical defoliation of L. salicaria within 3 weeks of anthesis should destroy the seed crop and prevent additions to the seed bank. (C)2000 Elsevier Science B.V. All rights reserved.