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United States Department of Agriculture

Agricultural Research Service


Location: Subtropical Horticulture Research

2010 Annual Report

1a. Objectives (from AD-416)
The primary goals for this project are to conserve, collect, evaluate, and distribute germplasm and associated information for subtropical/tropical fruit, sugarcane, and Tripsacum. A secondary goal is to investigate the genetic basis of important horticultural traits such as disease resistance and to select improved germplasm. Molecular markers have been developed for genetic diversity analysis and for the production of molecular genetic linkage maps. Families of avocado, mango, and jackfruit have been produced that should allow the mapping of Quantitative Trait Loci (QTL) involved with disease resistance, fruit quality, and yield. A candidate gene approach (CGA) is also being used to find genes involved with disease resistance and for control of flowering. Establish at other National Plant Germplasm System sites duplicate, back-up field plantings of Subtropical Horticulture Research Station priority germplasm; rejuvenate current Subtropical Horticulture Research Station field collections in Miami; and, as determined by annual demand, expand the curatorial capacity for distributing germplasm of sugarcane and tropical/subtropical tree crops.

1b. Approach (from AD-416)
Maintain healthy field collections of current accessions of tropical/subtropical fruit trees and grasses. We recognize that the genetic diversity available in tropical fruit species is not fully represented in the current collections. Significant loss of biodiversity and increasing difficulty in collecting germplasm in tropical countries makes it imperative that new accessions be collected as quickly as possible. Implement improved horticultural practices to ensure the longevity of current collections by re-propagating old clones on new rootstocks in new fields. Add new accessions as they become available from foreign collaborators and breeding programs. Because most of the species and location priorities for collection have been established, it is essential that we support international collecting expeditions with appropriate benefit sharing. After quarantine requirements have been satisfied, the new accessions will be maintained in field plantings. Backup core collections have been established in Mayaguez, Puerto Rico or Hilo, Hawaii. Adequate daily maintenance and periodic replanting of the sugarcane and Tripsacum collection is required to maintain these genetic resources, some 1,800 accessions, as healthy clones.

3. Progress Report
A genetic linkage map has been developed for avocado and Quantitative Trait Loci (QTLs) have been identified. Two thousand additional seedlings were obtained from California to expand the number of seedlings in the ‘Hass’ x ‘Bacon’ mapping population. The redbay ambrosia beetle, Xyloborus glabratus Eichhoff was introduced into the U.S. near Savannah, GA in 2002. The fungus infects and kills other members of Lauraceae including avocado, Persea americana Mill., and has been found in Palm Beach County. The USDA-ARS-NPGS (National Plant Germplasm System) collection of avocado is conserved at the NGR in Miami-Dade County Florida. Although the avocado collection is currently free from the ambrosia beetle and the laurel wilt disease, it is believed to be only a matter of time before this insect/disease complex reaches the collection. We have developed a protocol to secure the USDA ARS, NPGS avocado collection at Miami.

4. Accomplishments
1. Development of the highly resolved linkage map for the Florida avocado population. (Simmonds x Tonnage and reciprocal) has allowed the identification of QTLs for cold damage, thrip resistance and flowering type (A vs. B).

2. A protocol was developed to secure the avocado collection from the threat of Laurel Wilt. The protocol has three different activities. First, using the ARS Foreign Disease/Weed Science lab in Fort Detrick, MD as an intermediate quarantine, rootstocks were grown from seed sent from Miami. Staff from the NGR in Miami hand -carried scions to Ft. Detrick in August 2009 and grafted them onto the rootstocks. This procedure was repeated again in July of 2010 and now all non-ASBVd positive clones have been grafted at Fort Detrick. The grafted scions will remain in the greenhouse for a least one year or longer as necessary to ensure successful establishment in Hawaii. In July 2010 the first set of scions were sent from Fort Detrick to Hilo and grafted. Second, a backup collection has been grafted in the greenhouse in Miami. Third, research is ongoing at the National Center for Genetic Resource Preservation (NCGRP) to maintain avocado buds and meristems under cryogenic storage.

3. Enhancement of the sugarcane collection was accomplished by the addition of the 40 Saccharum officinarum accessions obtained from Barbados and Guadeloupe. Additionally seed of over 150 of S. officinarum and spontaneum accessions from the NCGRP have been germinated and will be added to the collection. The mango collection was increased with the addition of 52 accessions, cacao increased by 14 accessions, Pouteria sapote (mamey) collection increased by 8 accessions and the avocado collection was increased by 20 accessions.

5. Significant Activities that Support Special Target Populations
Mango fruit from varied accessions is supplied to collaborators at Fairchild Tropical Botanic Garden as part of their special weekend event on mangos that draws more than 10,000 residents.

Review Publications
Ayala Silva, T., Schnell Ii, R.J. 2010. THE TROPICAL AND SUBTROPICAL GERMPLASM COLLECTIONS AT THE NATIONAL GERMPLASM REPOSITORY IN MIAMI, FL. Journal of American Pomological Society. 64(1):28-37.

Schnell Ii, R.J., Tondo, C.L., Brown, J.S., Ayala Silva, T., Borrone, J.W., Davenport, T.L., Kuhn, D.N. 2009. Out-crossing between 'Bacon' pollinizers and adjacent 'Hass' avocado trees and the description of two new lethal mutants. HortScience. 44(6):1522-1526.

Brown, J.S., Schnell Ii, R.J., Ayala Silva, T., Moore, J.M., Tondo, C.L., Winterstein, M.C. 2009. Broad-sense heritability estimates for fruit color and morphological traits from open-pollinated half-sib mango families. HortScience. 44(6):1-5.

Postman, J.D., Bretting, P.K., Kinard, G.R., Cyr, P.D., Weaver, B., Millard, M.J., Gardner, C.A., Bohning, M.A., Emberland, G.P., Sinnott, Q.P., Ayala Silva, T., Hummer, K.E., Franco, T., Mackay, M., Guarino, L. 2010. GRIN-Global: An International Project to Develop a Global Plant Genebank Information Management System. Acta Horticulturae. 859:49-55.

Last Modified: 06/28/2017
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