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United States Department of Agriculture

Agricultural Research Service


Location: Subtropical Horticulture Research

2011 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
Two thousand seedlings were obtained from California to expand the number of seedlings in the ‘Hass’ x ‘Bacon’ mapping population. These were planted in Miami and at the ARS station in Ft. Pierce, FL for evaluation. The redbay ambrosia beetle, Xyloborus glabratus Eichhoff was introduced into the U.S. near Savannah, GA in 2002. The symbiotic fungus (Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva,) carried by the beetle infects and kills members of Lauraceae including avocado, Persea Americana Mill., and has been found in Palm Beach County, Florida. The USDA ARS National Plant Germplasm System (NPGS)collection of avocado is conserved at the National Germplasm Repository 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 and to establish a backup collection at the ARS germplasm repository in Hilo, HI. With funding provided from Office of National Program, we have sequenced the transcriptome of the parents of our avocado mapping populations and identified over 100,000 Single Nucleotide Polymorphism (SNP) markers. These have been filtered and a 6000 marker SNP chip has been designed and will soon be fabricated. This chip will be used on both mapping populations and on the entire germplasm collection. Genotyping of the mapping populations will saturate the genetic recombination maps and improve the resolution of Qualitative Trait Loci QTLs for cold tolerance, oil content and composition, and other agronomic traits. Genotyping of the entire germplasm collection will make possible the association of unique traits in the collection with genetic markers.

4. Accomplishments
1. 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 National Germplasm Repository 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 2011 and now all non-Avocado Sun Blotch Viroid positive clones have been grafted at Fort Detrick. The grafted scions will remain in the greenhouse for at least one year or longer as necessary to ensure successful establishment in Hawaii. Two sets of scions have been 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. The impact of these backup locations is an attempt to preserve the avocado collection.

2. Enhancement of the sugarcane collection was accomplished by the addition of 2,000 S. spontaneum seedlings germinated from 150 maternal clones. These seedlings are under evaluation for vigor and enhanced biomass production. 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. The impact of these activities is to conserve and collect tropical/subtropical fruit for the future.

Review Publications
Reed, S.T., Joseph, R., Ayala Silva, T., Glaz, B.S. 2011. The effects of natural and induced short-term floods on four sugarcane accessions. International Sugar Journal. 113:64-70.

Gunes, E., Gubbuk, H., Ayala Silva, T., Gozlekci, S., Ercisli, S. 2011. Effects of various treatments on seed germination and growth of carob (Ceratonia siliqua L.). Pakistan Journal of Botany. 39(1):251-254.

Schnell Ii, R.J., Tondo, C.L., Kuhn, D.N., Winterstein, M.C., Ayala Silva, T. 2011. Spacial analysis of avocado sunblotch disease in an avocado germplasm collection. Journal of Phytopathology. DOI: 10.1111/j.1439-0434.2011.01838.x.

Last Modified: 06/26/2017
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