DISTRIBUTION OF ANACARDIC ACIDS ASSOCIATED WITH SMALL PEST RESISTANCEAMONG CULTIVARS OF PELARGONIUM X HORTORUM

Composition of anacardic acids (phenolic acids known to be associated with small pest resistance in Pelargonium xhortorum) was examined in 1 3 diploid and 25 tetraploid cultivars by high-performance Liquid chrom atography (HPLC). The presence of an unusual desaturation (omega (omeg a)-5) in the alkyl tail of anacardic acids present only in glandular t richome exudate of pest-resistant diploid inbred lines had previously been associated with a sticky-trap pest-resistance phenomenon. In this study, we examine Pelargonium cultivars for variability in anacardic acid composition to assess the distribution of omega 5 desaturation am ong commercial cultivars, to determine possible interactions between o mega 5 desaturation and other plant desaturation mechanisms, and to ex amine the possible impact of ploidy on omega 5 desaturation. An unsatu ration index (UI) is derived to compare exudates differing widely in c omposition yet which may provide a similarly effective sticky-trap pes t-resistance mechanism based on exudate viscosity. omega-5 Anacardic a cids were observed in the glandular trichome exudate of all 38 commerc ial cultivars examined. No diploid cultivar produced omega 5- and omeg a 9-anacardic acids, although the simultaneous production of omega 5 a nd omega 9-anacardic acids was observed in three tetraploid cultivars. Total omega 5-anacardic acids comprised from 42.4% (tetraploid cultiv ar Perlenkette-syn. Snowhite, Weiss) to 86.8% (tetraploid cultivar Ama nda). Commercial P. xdomesticum cultivars had no omega 5 anacardic aci ds. UIs ranged from 60.9 (tetraploid cultivar Dixieland) to 103.4 (dip loid cultivar Pinto White). In contrast, anacardic acids collected fro m a pest-susceptible inbred line contained no omega 5-anacardic acids and had a UI of 38.7. No significant differences among ploidy levels w ere observed for UIs or for most specific anacardic acid components, w ith the exception of 24:1 omega 5-anacardic acid, in which the mean di ploid value (32.1%) was significantly higher than that of the mean tet raploid value (27.6%). We conclude that omega 5-anacardic acid product ion occurs in all Pelargonium cultivars observed and that these cultiv ars are predicted to exhibit resistance to small arthropod pests, Sign ificant genetic variability in specific anacardic acid composition app ears to exist among Pelargonium cultivars, suggesting that breeding fo r pest resistance can be readily monitored by HPLC of anacardic acids.