Differentiation of mistletoes on the basis of geographical origin using capillary gas chromatography and multivariate analysis.

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Looney, Michael
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Middle Tennessee State University
Multivariate statistical analysis of gas chromatographic data has been applied to the differentiation of species of mistletoe based on their geographic origin. Mistletoe plants were collected from 26 locations in Texas and 13 locations in Tennessee, Alabama, Georgia, and Florida. Hexane extractions were analyzed by split injection capillary gas chromatography. The column used was a Hewlett Packard capillary column Ultra 1, 25-meters long with an I. D. of 0.2 millimeters and a film thickness of 0.11 micrometers. The oven was programmed from {dollar}100\sp\circ\rm C{dollar} to {dollar}315\sp\circ\rm C{dollar} at a rate of {dollar}7.5\sp\circ\rm C{dollar} per minute and then held at {dollar}315\sp\circ\rm C{dollar} for 30 minutes.
When the normalized chromatographic data were subjected to principal component analysis and hierarchical cluster analysis, two main clusters were seen. One contained only Texas samples and the other contained southeastern United States samples plus several Texas samples, possibly due to overlapping ranges of the species and/or seasonal variation. Texas samples were also evaluated separately. Two clusters were observed: one consisted of samples from north Texas and the other from south Texas. Some overlap of samples did occur probably due to an extended growth range of some species and/or subspecies.
The effects of different hosts and seasonal variation were evaluated using similarity indices. Samples were collected from four different hosts in and around Kerrville, Texas. In some cases, there was as much variation between samples from the same type of host as there were between hosts. Samples were collected from the same mistletoe plant monthly for nine consecutive months. Notable seasonal variations were detected, with the greatest difference occurring between the months of November and April.
This method appears to have value as a chemotaxonomic technique for the differentiation of mistletoes, but further study is warranted. Compounds that are independent of host, season, gender, and method of collection must be carefully selected for use in speciation of mistletoe.