Browsing by Author "Alan W. Meerow"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Ambiguous genetic relationships among coconut (Cocos nucifera L.) cultivars: the effects of outcrossing, sample source and size, and method of analysis
    (2010) Margarita Mauro-Herrera; Alan W. Meerow; Lalith Perera; Joanne Russell; Raymond J. Schnell;
    A prior analysis of eight coconut cultivars with 15 microsatellite (SSR) markers drew unexpected relationships between two of the out-crossing tall cultivars evaluated: ‘Atlantic Tall’ and ‘Panama Tall’. We further investigated the relationships between these eight cultivars by increasing the number of individuals studied (particularly for ‘Atlantic Tall’ and ‘Panama Tall’), by including 28 more molecular markers, and by adding two other cultivars to our analysis. Our results show that five to ten coconut individuals do not represent a dependable sample to withdraw conclusions regarding cultivar/variety relationships, particularly when studying out-crossing genotypes. As suggested in the prior study, a high level of hybridization was observed between the ‘Atlantic Tall’ and ‘Panama Tall’ cultivars. However, at this time we were able to identify distinct groups for each one of these two cultivars. The two clustering methods used (Neighbor Joining, NJ and Unweighted Pair Group Method with Arithmetic mean, UPGMA) produced dendrograms that resolved contrasting cultivar relationships, especially for the ‘Atlantic Tall’ and ‘Panama Tall’ cultivars. We discuss the implications of our results in regard to current scenarios of coconut domestication and future considerations when assessing genetic relationships among different varieties.
  • Thumbnail Image
    Item
    Analysis of genetic diversity and population structure within Florida coconut (Cocos nucifera L.) germplasm using microsatellite DNA, with special emphasis on the Fiji Dwarf cultivar
    (2003) Alan W. Meerow; Randall J. Wisser; Steven Brown, J.; David N. Kuhn; Raymond J. Schnell; Timothy K. Broschat
    Using 15 simple sequence repeat (SSR) microsatellite DNA loci, we analyzed genetic variation within Cocos nucifera germplasm collections at two locations in south Florida, representing eight cultivars. The loci were also used in a parentage analysis of progeny of the ‘Fiji Dwarf’ variety at both locations. A total of 67 alleles were detected, with eight the highest number at any one locus. These loci identified 83 of the 110 individual palms. Gene diversity of the 15 loci ranged from 0.778 to 0.223, with a mean of 0.574. ‘Fiji Dwarf’, ‘Malayan Dwarf’, ‘Green Niño’ and ‘Red Spicata’ cultivars resolve as distinct clusters in a neighbor joining tree using modified Rogers distance, while the tall varieties form two aggregates. The highest gene diversity was found in the tall cultivars (Hˆ = 0.583 cumulatively), and the lowest in the ‘Malayan Dwarf’ (Hˆ = 0.202). After the tall coconuts, the ‘Fiji Dwarf’ was most genetically diverse (Hˆ = 0.436), and had the largest number of unique alleles. Genetic identity is highest among the ‘Malayan Dwarf’ phenotypes, and between the tall varieties. The ‘Red Malayan Dwarf’ is genetically distinct from the ‘Green’ and ‘Yellow Malayan Dwarf’ phenotypes, which cannot be distinguished with the SSR loci used. Off-type ‘Malayan Dwarf’ phenotypes (putative hybrids with talls) can be identified genotypically. Parentage analyses of 30 ‘Fiji Dwarf’ progeny propagated from five adults surrounded by other cultivars estimate that only 20% of the progeny were out-crossed to the other varieties, while 40–46% were possible selfs. This suggests that a seed-production orchard of the variety maintained at reasonable distance from other varieties, will likely yield only ‘Fiji Dwarf’ genotypes. Our data are discussed in the context of hypotheses of coconut dissemination around the world.
  • Thumbnail Image
    Item
    A computer simulation study on the number of loci and trees required to estimate genetic variability in cacao (Theobroma cacao L.)
    (2006) Cuauhtemoc Cervantes-Martinez; J. Steven Brown; Raymond Schnell; Juan C. Motamayor; Alan W. Meerow; Dapeng Zhang
    Current methods for measures of genetic diversity of populations and germplasm collections are often based on statistics calculated from molecular markers. The objective of this study was to investigate the precision and accuracy of the most common estimators of genetic variability and population structure, as calculated from simple sequence repeat (SSR) marker data from cacao (Theobroma cacao L.). Computer simulated genomes of replicate populations were generated from initial allele frequencies estimated using SSR data from cacao accessions in a collection. The simulated genomes consisted of ten linkage groups of 100 cM in length each. Heterozygosity, gene diversity and the F statistics were studied as a function of number of loci and trees sampled. The results showed that relatively small random samples of trees were needed to achieve consistency in the observed estimations. In contrast, very large random samples of loci per linkage group were required to enable reliable inferences on the whole genome. Precision of estimates was increased by more than 50% with an increase in sample size from one to five loci per linkage group or 50 per genome, and up to 70% with ten loci per linkage group, or equivalently, 100 loci per genome. The use of fewer, highly polymorphic loci to analyze genetic variability led to estimates with substantially smaller variance but with an upward bias. Nevertheless, the relative differences of estimates among populations were generally consistent for the different levels of polymorphism considered.
  • Thumbnail Image
    Item
    Ten informative markers developed from WRKY sequences in coconut in coconut (Cocos nucifera)
    (Blackwell Publishing Ltd, 2006) Margarita Mauro-Herrera; Alan W. Meerow; James W. Borrone; David N. Kuhn; Raymond J. Schnell
    Coconut ( Cocos nucifera L.) WRKY sequences containing single nucleotide polymorphisms (SNPs) and one microsatellite repeat were used to develop 10 informative markers. These markers were evaluated in 15 genotypes representing six coconut cultivars. SNP-containing alleles were detected by single-strand conformation polymorphism (SSCP) analysis. The number of detected alleles ranged from two to four. Five pairs of loci were in linkage disequilibrium in the test population. These markers are currently being evaluated in more individuals/ cultivars to determine their value in estimating the genetic diversity of this species.