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United States Department of Agriculture

Agricultural Research Service

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Research Project: SCREENING AVOCADO (PERSEA AMERICANA) GERMPLASM FOR TOLERANCE/RESISTANCE TO THE LAUREL WILT PATHOGEN (RAFFAELEA LAURICOLA)

Location: Subtropical Horticulture Research

Project Number: 6631-21000-022-02
Project Type: Reimbursable

Start Date: Feb 08, 2011
End Date: Aug 31, 2013

Objective:
1. To screen ARS germplasm collection maintained as the SHRS in Miami for tolerance/resistance to the disease. 2. To develop 10 to 30 thousand usable Simple Sequence Repeat (SSR) and Single Nucleotide Polymorphism (SNP) markers to saturate our current genetic linkage maps and to use for association mapping to locate genes involved with tolerance/resistance.

Approach:
Resistance/tolerance to Laurel Wilt will be evaluated by screening maternal half-sib families from each of the ~300 germplasm accessions in the collection. The seeds will be harvested over the next two seasons (June-November 2010 and 2011) and germinated at the USDA-ARS station in Ft. Pierce, FL. Our objectives are to screen 100 seedlings from each accession and to estimate the heritability of the disease resistance/tolerance from maternal parents conferring tolerance. The plants will be planted using ~four ha of the USHRL farm or alternatively the adjacent IFAS farm. The plants will be inoculated with Raffaelea lauricola in the field and scored for tolerance to the pathogen. Tolerant genotypes will be propagated for further testing. A subset of the 30,000 seedlings will be evaluated using microsatellite and SNP markers developed from NGS. Using the SNP chip array will allow us to map 15,000 loci in each individual in a single evaluation. Using this information, we will perform association mapping to determine areas of the avocado genome involved with tolerance to laurel wilt. Molecular analysis will be used to find associations between molecular markers and the tolerance as a tool for enhanced screening. Using next generation sequencing (NGS), thousands of SSR and SNP markers can be easily identified and used for increased map saturation and association genetics thus facilitating QTL identification. We will generate 10 x 454 coverage of the cultivar ‘Hass’ and 50x Illumina coverage for the other three parents of our mapping populations, ‘Bacon’, ‘Simmonds’, and ‘Tonnage’. The identification of 300,000 new SNP markers has been accomplished using this procedure with cacao (Theobroma cacao L.). The SNP markers will be used to develop an Illumina 30K SNP iSelect array.

Last Modified: 7/30/2014
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