Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2005
Publication Date: 3/15/2006
Citation: Schnell II, R.J., Brown, J.S., Olano, C.T., Meerow, A.W., Campbell, R.J., Kuhn, D.N. 2006. Mango genetic diversity analysis and pedigree inferences for florida cultivars using microsatellite markers. Journal of the American Society for Horticultural Science. 131(2):214-224. Interpretive Summary: A large collection of mango germplasm is maintained by the USDA, ARS, SHRS in Miami. This is a collection of large fruit trees and maintaining the maximum amount of genetic diversity with the minimum number of individuals is a critical management objective. One of the best ways to estimate genetic diversity in germplasm collections is with molecular markers. We developed 14 new microsatellite markers for mango and used these to estimate genetic diversity and propagation error among 223 accessions. Propagation error was estimated to be 6.0% a value similar to other error rates in vegetatively propagated tree crops. The mango germplasm can be divided by origin and by seed type. The primary origins are India, Southeast Asia, and Florida. The Florida group of mangos was found to be more similar to the Indian types than the Southeast Asian types and genetic diversity was lower among the Florida types that either of the other two. Mango can also be divided by seed type, polyembroynic vs. monembryonic, and genetic diversity was found to be greater among the polyembroynic types than the monembryonic types. A parentage analysis was performed on the Florida mangos based on date of selection and date of introduction of cultivars into Florida. The results suggest that a few as four Indian cultivars, the land race known as Saigon and the local Turpentine types were the parents of early Florida mango cultivars. The Florida group of cultivars are highly productive and the most successful commercial cultivars in the world producing dependably under many environmental conditions. Understanding the basis of this production stability will increase the efficiency of our breeding and selection programs for new mango cultivars.
Technical Abstract: Mangifera indica germplasm can be classified by origin with the primary groups being cultivars selected from the center of diversity of the species (India and Southeast Asia) and from Florida. Accessions can also be classified by horticultural race, monembryonic versus polyembryonic seed types. In this study we developed 14 new microsatellite loci using an enrichment protocol that gave amplification products to a single locus and consistent, interpretable results. These microsatellites were then used to estimate genetic diversity among 223 unique accessions maintained at the National Germplasm Repository (NGR) and by Fairchild Tropical Garden (FTG) in Miami, Florida. The 14 microsatellite loci had an average of 7.6 alleles per locus and an average Polymorphism Information Content (PIC) value of 0.462. The total propagation error in the collection, i.e., plants that had been incorrectly labeled or grafted, was estimated to be 5.9%. When compared by origin, the Florida types were more closely related to Indian than to Southeast Asian types. Average gene diversity (Hnb) of 0.51 and 0.47 was found for Indian and Southeast Asian types, respectively, and both were higher than Hnb among Florida types (0.452). When compared by horticultural race, Hnb was higher among the polyembroynic seed race (0.507) than in the monoembryonic seed race (0.48). Parentage analysis of the Florida cultivars was accomplished using a multistage process based on introduction dates of cultivars into Florida and selection dates of Florida cultivars. In total, 69 Florida cultivars were evaluated over four generations. Microsatellite marker evidence suggests as few as four Indian cultivars, the land race known as 'Saigon', and the criollo 'Turpentine' were involved in the early cultivar selections. The total number of parents identified from 1880- 2000 was 63; however, 37 of those were other Florida cultivars. The inbreeding coefficient among the Florida types is 0.254. Florida may not represent a secondary center of diversity but the Florida group is a unique set of cultivars selected under similar conditions offering production stability.