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Rafael Fernández-Muñoz, María Salinas, Marta Álvarez, and Jesús Cuartero

Genetics of resistance to Tetranychus urticae Koch and of glandular trichomes of Lycopersicon pimpinellifolium accession TO-937 in a cross between susceptible L. esculentum Mill. `Moneymaker' and resistant TO-937 was studied in a greenhouse experiment. Parents, F1, F2, and two BC1 generations, interspersed with susceptible tomato plants to avoid negative interplot interference, were artificially infested. Mite susceptibility was evaluated by a rating based on plant capacity to support mite reproduction. TO-937, BC1 to TO-937, and F1 were resistant, `Moneymaker' susceptible, and the F2 and the BC1 to `Moneymaker' segregated. Resistance was controlled by a single dominant major locus, but modulated by unknown minor loci. TO-937 presented type IV glandular trichomes, their presence governed by two dominant unlinked loci. Type IV trichome density correlated to resistance; however, a causal relationship between type IV trichomes and mite resistance could not be definitively established. The relatively simple inheritance mode will favor successful introgression of resistance into commercial tomatoes from the close relative L. pimpinellifolium.

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Zhenhua Guo and John C. Snyder

Choice and non-choice bioassays were used to examine deterrence in vitro and in vivo of Tetranychus urticae Koch. In vivo deterrence of leaflets from 11 Lycopersicon hirsutum accessions as well as the tomato cultivar `Ace 55' was measured as was in vitro deterrence of their leaf hexane extracts. Leaf surface chemistry was examined by gas chromatography. All 6 accessions of L. hirsutum f. hirsutum contained sesquiterpene hydrocarbons. Each of these extracts also contained one or a few late eluting components. All were deterrent in vitro and 5 out of the 6 were deterrent in vivo. The one lacking in vivo deterrence had low density of type IV trichomes. All 5 accessions of L. hirsutum f. glabratum contained methyl ketones. These accessions were less deterrent in vitro and 4 out of the 5, less deterrent in vivo. The one accession having high in vivo deterrence also had high density of type IV trichomes. `Ace 55', having few hexane extractable compounds was neither deterrent in vitro nor in vivo. Within an accession, secretions from different types of trichomes shared similar chemical profiles and were similar to leaf profiles.

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Barbara E. Liedl, Darlene M. Lawson, Kris K. White, Joseph A. Shapiro, William G. Carson, John T. Trumble, and Martha A. Mutschler

Acylsugars, the primary components of the exudate secreted by type IV trichomes of Lycopersicon pennellii (Corr.) D'Arcy LA716, mediate the resistance of this accession to silverleaf whitefly, Bemisia argentifolii Bellows & Perring, n. sp. Reduction in the settling of the adult silverleaf whiteflies correlates with the concomitant increase in applied acylsugars. Oviposition of B. argentifolii is also affected by acylsugars, resulting in a reduction in the number of eggs and nymphs found; however, acylsugars do not affect hatching of nymphs. The threshold amount of acylsugars required for deterring settling and oviposition is under the amount of acylsugars (50 to 70 μg·cm–1) required for control of other insects.

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J.C. Goffreda, J.C. Steffens, and M.A. Mutschler

Behavioral studies have shown that aphid resistance in Lycopersicon pennellii (Corr.) D'Arcy is due to the presence of sugar esters in glandular exudate of the type IV trichomes. In this study, various methods for the estimation of epicuticular sugar ester concentrations were examined. There was a significant negative relationship between the concentration of sugar esters on the leaf and the level of potato aphid infestation in a segregating L. esculentum × L. pannellii F2 population. Selection for sugar ester accumulation should be an efficient selection technique for the aphid resistance of L. pennellii and other species that synthesize epicuticular sugar esters.

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Dao-Jing Wang, Jing-Wen Zeng, Wen-Tao Ma, Min Lu, and Hua-Ming An

this genus. In rosaceous plants, detailed study on the type and distribution of the vegetative organ trichomes has been conducted only in Rubus and Rosas ( Coyner et al., 2005 ; Feng et al., 2015 ; Finn et al., 2008 ; Kellogg et al., 2011 ). These

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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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Aliya Momotaz, Jay W. Scott, and David J. Schuster

occurring allelochemicals present in single-lobed glandular trichomes (type IV) that do not occur in cultivated tomato ( Muigai et al., 2002 ). In S. pennellii , acylsugars present in type IV trichomes were related to whitefly resistance ( Blauth et al

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Dalia Taher, Mohamed Rakha, Srinivasan Ramasamy, Svein Solberg, and Roland Schafleitner

insect resistance and trichome types and densities has been reported for many plant species ( Mitchell et al., 2016 ; Tian et al., 2012 ). For the genus Solanum , eight types of trichomes have been identified, of which four (i.e., types I, IV, VI, and

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Martha A. Mutschler, Jian Hua Xiong, Ahmed Wally, and Ricardo Lobato-Ortiz

The wild tomato Lycopersicon pennellii is resistant to numerous important pests of cultivated tomato, L. esculentum, including armyworm, fruitworm, aphids, leafminers, and whitefly. The pest resistance of L. pennellii is mediated by the presence of acylsugars, which constitute 90% of L. pennelliitype IV trichome exudate. Transfer of the ability to accumulate acylsugars could result in pest-resistant tomato cultivars, and thus, a reduction in the dependence on synthetic chemicals for insect control for this crop. Initial tomato lines bred for acylsugar production possessed the desired insect resistance, but were of poor horticultural quality due to linkage drag. These tomato lines possessed seven or eight L. pennellii introgressions, some of which were quite large. As a result, about 25% to 30% of the genomes of these acylsugar lines were comprised of L. pennellii DNA. A set of 20 molecular markers was created, providing markers throughout each introgression. The acylsugar breeding program then combined use of a biochemical assay for acylsugars and genomic analyses using these molecular markers to determine which of the introgressions were involved in the linkage drag, and to select plants that either eliminated or shortened those introgressions. Introgressions on chromosomes 2, 3, 5, and 10 were found to be associated with negative characteristics, such as delayed germination, reduced fruit set or size, delayed maturity, or reduced seed set. New acylsugar lines that eliminate or reduce some of these introgressions were created. The new lines show marked improvement in some of the affected traits, while also producing acylsugars. Hybrids created using these lines show marked improvement in horticultural type.

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Sanford D. Eigenbrode and John T. Trumble

Four accessions of Lycopersicon hirsutum f. glabratum Mull. and eight accessions of L. hirsutum f. typicum Humb. & Bonpl. were evaluated for their resistance to the beet armyworm [Spodoptera exigua (Hübner)]. Survival of S. exigua neonate larvae for up to 96 hours on foliage of all these accessions differed significantly from their survival on a susceptible tomato cultivar. Spodoptera exigua survival did not differ significantly between the two forms of L. hirsutum. Antibiosis to S. exigua in L. hirsutum f. glabratum appears similar to the levels found to other Lepidoptera. Accessions of L. hirsutum f. typicum included the very susceptible PI 199381 and the two most resistant accessions, LA 2329 and LA 1777. Insect resistance had not been reported previously in four of the L. hirsutum f. typicum accessions. Spodoptera exigua survival was significantly negatively correlated with the density of type IV glandular trichomes on the leaf surfaces, calculated across all 12 accessions. This relationship did not occur within L. hirsutum f. glabratumor L. hirsutum f. typicum accessions, nor was it significant if PI 199381 was excluded from the analysis. Leaf-surface exudates of L. hirsutum f. glabratum accessions were dominated by the methylketones 2-undecanone and 2-tridecanone. Leaf-surface exudates of L. hirsutum f. typicum were dominated by three sesquiterpenes-zingiberene, δ elemene, and γ elemene. Resistance was not correlated with the amounts of these specific compounds within or across botanical form. Spodoptera exigua survival in L. hirsutum f. typicum (excluding PI 199381) correlated negatively with the total estimated amount of leaf-surface volatiles extracted. PI 199381 may be useful as a susceptible parent for intraspecific crosses to examine S. exigua resistance in L. hirsutum.