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This work was carried out while the author was a Visiting Research Geneticist at the University of California, Riverside. We thank the California Avocado Advisory Board for its generous grant support, Ms. Janet Lee for technical assistance, Mr. Robert Whitsell for harvesting materials used, Dr. Carl W. Campbell, and Dr. George Zentmyer, who provided fruit of Florida cultivars and many of the Persea spp., respectively. Drs. Christopher Haufler and Robert K. Soost kindly read the manuscript. The work was supported in its early stages by NSF grant DEB76-10777.