In vitro selection of duckweed geographical isolates for potential use in swine lagoon effluent renovation

Plant-based systems for nutrient sequestration into valuable biomass have t he potential to help avoid the environmental problems associated with the d isposal of large volumes of animal waste. The objective of this study was t o select superior duckweed (Lemnaceae) genotypes for the utilization of nut rients in animal wastes. A two-step protocol was used to select promising d uckweed geographic isolates to be grown on swine lagoon effluent. Forty-one geographic isolates from the worldwide germplasm collection were used in a n in vitro screening test, because they were noted to be fast-growing genot ypes during routine collection maintenance. In vitro screening was accompli shed by growing geographic isolates on a synthetic medium that approximated swine lagoon effluent in terms of nutrient profile, total ionic strength, pH, and buffering capacity. Large differences among geographic isolates wer e observed for wet weight gain during the Ii-day growing period, percent dr y weight, and percent protein in dry biomass. Total protein production per culture jar differed 28-fold between the most disparate of the 41 geographi c isolates and was the variable used for selection of superior geographic i solates. The challenge of eight of the 41 geographic isolates with full-str ength swine lagoon effluent in the greenhouse led to the selection of three that are promising as genotypes to be grown on lagoon effluent. (C) 2000 E lsevier Science Ltd. All rights reserved.