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Richard Grazzini, David Hesk, Ellen Yerger, Diana Cox-Foster, June Medford, Richard Craig, and Ralph O. Mumma

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.

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Martha A. Mutschler, Edward D. Cobb, Barbara E. Liedl, and Joseph A. Shapiro

Acylsugar mediates the resistance of Lycopersicon pennellii LA716 to several important insect pests of cultivated tomato, including potato aphid, green peach aphid, leaf miner, fruitworm, armyworm, and silverleaf whitefly. Incorporation of acylsugar-mediated multiple pest resistance could result in a significant reduction in the use of pesticidal sprays in cultivated tomato. Development of a reliable assay for acylsugar production and confirmation of the association between the resistance and acylsugars allowed us to try to breed for the trait by selecting for acylsugar-producing plants. The breeding cycle allows us to progress by one backcross generation per year. The breeding program was faced by several challenges, including interference in gene transfer by interspecific crossing barriers, and the oligogenic nature of the acylsugar-mediated resistance trait. Despite these challenges, the breeding program has produced BC3F2 plants that produce effective levels of acylsugars, are tomato-like in vine appearance, and produce seed-bearing fruit in the field without manual pollination. The current status of the program and future plans will be discussed.

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Sanford Eigenbrode and Jimmy Tipton

Mexican redbud (Cercis canadensis var. mexicana) exhibits resistance to leaf cutter bees (Megachile spp., LCB). Resistant trees (CMG) have glossy leaves and sustain little LCB damage as compared to dull-leaf Mexican redbud (CMD) and the closely related eastern redbud (Cercis canadensis, CC). On average, LCB made 35 times as many cuts per week on CC as on CMG and CMD, even though there were half as many leaves available. Mexican redbud leaves are twice as thick as CC leaves, which may account for LCB preference for the latter. However, leaves from CMG and CMD are similar in leaf thickness, cuticle wax content, and resistance to penetration, yet LCB had an even stronger preference for the former. More than 83 times as many cuts per week were made on CMD over CMG, even though the number of leaves was comparable. CMG leaves have a thicker cuticle on the upper surface that lacks wax crystals present in the CMD and CC. The upper cuticle from CMG leaves also contains fewer lipids and an altered lipid composition (notably fewer long-chain alcohols) compared to CMD.

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Richard Grazzini, David Hesk, Ellen Yerger, Diana Cox-Foster, June Medford, Richard Craig, and Ralph O. Mumma

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.

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Martha A. Mutschler, Rebecca W. Doerge, Sin-Chieh Liu, Jian P. Kuai, Barbara E. Liedl, and Joseph A. Shapiro

Lycopersicon pennellii, a wild relative of the tomato, L. esculentum, is resistant to a number of important pests of cultivated tomato due to the accumulation of acylsugars, which constitute 90% of L. pennellii LA716 type IV trichome exudate. An interspecific F2 population created by crossing L. esculentum × L. pennellii was surveyed for acylsugar accumulation and subjected to RFLP analysis to determine the genomic regions associated with the levels of acylglucoses, acylsucroses, and total acylsugars accumulated, and glucose as a percentage of total acylsugars. Data was analyzed using MAPMAKER with and without log10 transformation and using a threshold of either 2.4 (default value for MAPMAKER) or ones calculated according to the Permutation-based Estimated Threshold (PET) method. Genomic regions were identified for each of the traits studied. Effects of analytical method on identification of QTLs, similarities between these results and results published for the genus Solanum, and similarities between these results and the regions transferred by a breeding program selecting for acylsugar production are discussed.

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Cynthia A. Patton, Thomas G. Ranney, James D. Burton, and James F. Walgenbach

Feeding intensity of adult Japanese beetle (Popillia japonica Newm.) was compared among 27 taxa of Prunus host plants during 24-hour no-choice feeding trials conducted on individual leaves. Fecal dry mass per beetle, a measure of feeding intensity, varied from 0 mg·d-1 for Prunus padus L. to 20.4 mg·d-1 for P. sargentii Rehd. and P. tomentosa Thunb. Prunus padus, P. laurocerasus L., P. mahaleb L., P. serotina Ehrh., P. virginiana L., P. americana Marsh., P. ×yedoensis Matsum., and P. besseyi Bailey were resistant based on feeding intensities of <4.3 mg·d-1 (levels not significantly different from zero). Feeding intensity decreased exponentially as endogenous foliar cyanide potential increased. Evaluation of the cyanogenic glucoside prunasin in artificial diets showed a similar relationship with feeding being reduced by 50% (ED50) at 4.9 mmol·kg-1 in the diet. Prunus mahaleb was highly resistant to Japanese beetles despite having low cyanide potential. Two coumarin compounds known to exist in P. mahaleb, herniarin and coumarin, were tested in artificial diets and were effective feeding deterrents with ED50 values of 5.9 and 2.5 mmol·kg-1 in the diet, respectively. This research demonstrated a wide range of host plant resistance to feeding by adult Japanese beetles and further indicates that prunasin, herniarin, and coumarin are important factors in host plant resistance to this pest.

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Scott C. Redlin, Dale E. Herman, and Larry J. Chaput

Pekin lilac ( Syringa pekinensis Rupr.), a tree lilac native to northern China, has many desirable horticultural traits but is underused as a landscape plant ( Dirr, 1998 ). A combination of pest resistance and superior ornamental characteristics

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Kelechi Ogbuji, Gloria S. McCutcheon, Alvin M. Simmons, Maurice E. Snook, Howard F. Harrison, and Amnon Levi

://www.ars-grin.gov ) includes over 1800 U.S. PIs. These PIs have been useful sources of germplasm for identifying disease or pest resistance that through intensive breeding programs could be incorporated into elite watermelon cultivars. Whiteflies [ Bemisia tabaci (Gennadius

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John L. Coffey, Alvin M. Simmons, B. Merle Shepard, Yaakov Tadmor, and Amnon Levi

, Plant Genetic Resources Conservation Unit at Griffin, GA; the unit maintains 24 PIs classified as C. colocynthis . Seeds for nine additional genotypes of C. colocynthis , which lacked screening for pest resistance and were collected in Israel, were

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E.C. Tigchelaar and V.L. Foley