|Schnell Ii, Raymond|
|Motamayor, Juan Carlos|
Submitted to: American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2003
Publication Date: 11/20/2003
Citation: Schnell II, R.J., Brown, J.S., Olano, C.T., Power, E.J., Krol, C.A., Kuhn, D.N., Motamayor, J. 2003. Evaluation of avocado germplasm using microsatellite markers. American Society for Horticultural Science. Interpretive Summary: The avocado germplasm collection at the National Germplasm Respository located on the Subtropical Horticultural Research Station is one of the major collections maintained at the Repository. This collection had not been evaluated for genetic diversity using molecular markers. Using previously published DNA primer sequences for 14 microsatellite markers, we evaluated the collection. Twenty-nine accessions from the University of California South Coast Field STation in Irvine were included in the evaluation for a total of 434 plants representing 254 accessions. These markers are very useful for DNA fingerprinting and for genetic diversity analysis. Avocado germplasm has been classified into three horticultural races: Guatemalan, Mexican, West Indian, and interracial hybrids. Using Principal Coordinate Analysis (PCA) based on gene frequency, the populations clustered in three major groups representing the three races. Some misclassifications were identified and the racial status of 49 (19.3%) of the accessions was changed. The interracial hybrid groups Guatemalan x Mexican, Guatemalan x West Indian, and Mexican x West Indian all clustered between the respective racial groups. Genetic diversity estimates were high for the Mexican and Guatemalan race and lower for the West Indian race, indicating that genetic diversity is not as high among the West Indian accessions. Based on these data we will be actively collecting new West Indian accessions from Central America to broaden the genetic diversity and to look for resistance to Phytophthora Root Rot.
Technical Abstract: Three horticultural races of avocado are known: Guatemalan, Mexican, and West Indian. Each races has unique characteristics and current commercial varieties have been selected from within the races or from interracial hybrids. Utilizing 14 microsatellite loci we investigated the genetic variation in a large collection, 225 accessions (405 plants), maintained at the National Germplasm Repository (NGR) in Miami, FL and a set of clones, 29 accessions, from the University of California South Coast Field Station (SCFS) located in Irvine, CA. The 14 microsatellite loci had an average of 18.7 allels per locus and average unbiased genetic diversity was 0.83. The total propagation error in the collection was estimated to be 7.4%, plants that had been incorrectly labled or grafted. Principal Coordinate Analysis (PCA) grouped the Guatemalan and Mexican races into two distinct clusters. The West Indian also grouped into a unique major cluster but with an outlying group. Using the PCA, the racial designation or interracial hybrid status of 49 accesions (19.3%) was changed. The Guatemalan x Mexican, Guatemalan x West Indian, and Mexican x West Indian racial hybrids all clustered between the respective distinct populations. The unbiased gene difersity estimate was highest in the Mexican and Guatemalan races and lower in the West Indian group. This emphasizes the need to collect more of the West Indian germplasm to increase the genetic diversity and to identify individuals conferring resistance to Phytophthora Root Rot (PRR).