Abstract
Chemical analyses were conducted to determine the qualitative and quantitative differences in monoterpenes and sesquiterpenes in plant material from avocado trees, Persea americana Mill. (Lauraceae). The initial study analyzed plant material sampled from the trunk to the leaves through different branch diameters to quantify proximo-distal spatial differences within a tree. All trees were seedlings initiated from a single maternal tree. Two-way analysis of variance was conducted on 34 chemicals that comprised at least 3% of the total chemical content of at least one tree and/or location within a tree. There were significant interactions between genotype and location sampled for most chemicals. Parentage analysis using microsatellite molecular markers (SSR's) determined that the four trees had three fathers and that they represented two full-siblings and two half-sibling trees. Descriptive discriminant analysis found that both genotype and location within a tree could be separated based on chemical content, and that the chemical content from full-siblings tended to be more similar than chemical content from half-siblings. To further explore the relationship between genetic background and chemical content, samples were analyzed from leaf material from 20 trees that included two sets of full-sibling seedling trees, the maternal tree and the surviving paternal tree. Descriptive discriminant analysis found good separation between the two full-sibling groups, and that the separation was associated with chemistry of the parental trees. Six groups of chemicals were identified that explained the variation among the trees. We discuss the results in relation to the discrimination process used by wood-boring insects for site-selection on host trees, for tree selection among potential host trees, and the potential use of terpenoid chemical content in chemotaxonomy of avocado trees.
Highlights
Plants display a large diversity of secondary metabolites, among which terpenoids are the largest class, with approximately 50,000 structurally identified [1]
Using a combination of chemical analysis of the terpenoid content of seedling trees grown from seeds of a known maternal parent, and genetic analysis with microsatellite molecular markers to determine paternal parent, we addressed the following questions: Are qualitative and quantitative spatial differences present in the chemical phenotype in avocado trees? How do the terpenoids differ spatially from the trunk through the branches to the leaves? Does the variability in chemical profiles allow for an accurate separation between halfand full-sibling avocado trees?
Little is known about the mechanisms underlying rejection of non-host tree species by wood-boring beetles
Summary
Plants display a large diversity of secondary metabolites, among which terpenoids are the largest class, with approximately 50,000 structurally identified [1]. Terpenoids, primarily C10 monoterpenes and C15 sesquiterpenes, are known to play an important role in the biology and ecology of plants, directly or indirectly influencing their interactions with the environment. Plants generally produce complex mixtures of terpenoids that may differ greatly among species. Plant populations exhibit a large amount of phenotypic chemical variation in terpenoid content. Terpenoids are known to play various roles in the plant kingdom. They have been identified to be responsible for attraction of insects to host plants [7], [8]. Terpenoids can be emitted from herbivore-damaged plants to attract natural enemies and indirectly confer plant defense [12]
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