Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: Richard Grazzini x
Clear All Modify Search

Resistance to mites and small insects in geranium results from the production of a viscous exudate on tall glandular trichomes present on the plant surface. This exudate exhibits sticky-trap properties immobilizing pests and reducing feeding and fecundity. The exudate is composed of long-chain 6-alkyl salicylic acids known as anacardic acids. The exudate of resistant plants contains 86% unsaturated anacardic acids. Susceptible genotypes possess fewer tall glandular trichomes and a trichome exudate which is dry and ineffective in trapping pests. The exudate from susceptible plants contains 70% saturated anacardic acids, thus explaining the physical state of the exudate. A single dominant locus controls the production of predominantly unsaturated versus saturated anacardic acids and thus resistance versus susceptibility. Other loci condition the ratio of C22:C24 unsaturated anacardic acids and the density of tall glandular trichomes. Current research involves the elucidation of the enzymatic pathway(s) involved in anacardic acid biosynthesis, identification of the regulatory enzymes and isolation of the mRNA transcripts associated with pertinent genes.

Free access

Biochemical and morphological components of 16 Pelargonium species and the P. ×hortorum interspecific complex were examined. Inflorescences and leaves of each species were analyzed for anacardic acids and the presence of glandular trichomes. Three species of the section Ciconium, P. acetosum, P. frutetorum, and P. inquinans, produced anacardic acids in association with glandular trichomes. only P. inquinans and P. frutetorum contained ω5- anacardic acids. An evolutionary model for the origin of anacardic acids and ω5- desaturation is proposed.

Free access

Composition of anacardic acids (phenolic acids known to be associated with small pest resistance in Pelargonium ×hortorum) was examined in 13 diploid and 25 tetraploid cultivars by high-performance liquid chromatography (HPLC). The presence of an unusual desaturation (omega (ω)-5) in the alkyl tail of anacardic acids present only in glandular trichome 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 ω5 desaturation among commercial cultivars, to determine possible interactions between ω5 desaturation and other plant desaturation mechanisms, and to examine the possible impact of ploidy on ω5 desaturation. An unsaturation index (UI) is derived to compare exudates differing widely in composition yet which may provide a similarly effective sticky-trap pest-resistance mechanism based on exudate viscosity. ω-5 Anacardic acids were observed in the glandular trichome exudate of all 38 commercial cultivars examined. No diploid cultivar produced ω5- and ω9- anacardic acids, although the simultaneous production of ω5 and ω9- anacardic acids was observed in three tetraploid cultivars. Total ω5- anacardic acids comprised from 42.4% (tetraploid cultivar Perlenkette-syn. Snowhite, Weiss) to 86.8% (tetraploid cultivar Amanda). Commercial P. ×domesticum cultivars had no ω5 anacardic acids. UIs ranged from 60.9 (tetraploid cultivar Dixieland) to 103.4 (diploid cultivar Pinto White). In contrast, anacardic acids collected from a pest-susceptible inbred line contained no ω5- anacardic acids and had a UI of 38.7. No significant differences among ploidy levels were observed for UIs or for most specific anacardic acid components, with the exception of 24:1 ω5- anacardic acid, in which the mean diploid value (32.1%) was significantly higher than that of the mean tetraploid value (27.6%). We conclude that ω5- anacardic acid production occurs in all Pelargonium cultivars observed and that these cultivars are predicted to exhibit resistance to small arthropod pests. Significant genetic variability in specific anacardic acid composition appears to exist among Pelargonium cultivars, suggesting that breeding for pest resistance can be readily monitored by HPLC of anacardic acids.

Free access

Diploid zonal geraniums (Pelargonium ×hortorum) are able to resist attack by small arthropod pests such as the two-spotted spider mite (Tetranychus urticae Koch) when exudate produced by tall glandular trichomes contains a high percentage of ω5-unsaturated anacardic acids. Trichomes of susceptible plants exude primarily saturated anacardic acids. Inbred mite-resistant and -susceptible geraniums were reciprocally crossed and the F1, F2, and backcross generations were examined for anacardic acid composition and trichome density. Selected F2 plants were bioassayed for resistance to two-spotted spider mites. High concentrations of ω5-unsaturated anacardic acids in resistant plants are conditioned by a single dominant allele. We propose that inheritance of tall glandular trichome density can be controlled by a small number of loci (possibly as few as one) exhibiting codominance. F2, with low densities of tall glandular trichomes and producing ω5-unsaturated anacardic acids, displayed effective resistance to two-spotted spider mites as measured by mite mortality and fecundity. A genetic model for the biosynthesis of anacardic acids is proposed.

Free access