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J.W. Scott and J.P. Jones

Forty-two Lycopersicon pennellii Corr. D'Arcy accessions, from the Tomato Genetics Stock Center, were inoculated for resistance to Fusarium wilt race 3 at the 3-leaf and cotyledon stage. All were over 90% healthy when inoculated at the 3-leaf stage but had greater disease incidence at the cotyledon stage. Crosses were made between healthy plants within each accession. Using this seed, 39 accessions were 100% healthy and 3 were over 96% healthy when inoculated at either stage. Seventeen F1's with susceptible parents were tested for race 3 and all had over 80% healthy plants. Twenty-two accessions were tested for Fusarium wilt race 1 and race 2. For race 1, 21 were 100% healthy and 1 was 91% healthy, For race 2, 20 were 100% healthy, 1 was 96% healthy, and 1 was 75% healthy. Forty accessions were screened for Fusarium crown rot and Verticillium wilt. For crown rot, LA 1277, LA 1367, and LA 1657 were over 95% healthy, 6 other accessions were over 68% healthy and several others had over 50% healthy plants, All 40 were susceptible to Verticillium wilt race 1. L. pennellii appears to be a good source of resistance to Fusarium sp. but not to Verticillium wilt.

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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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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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J.W. Scott and J.P. Jones

Lycopersicon pennellii accession LA 1277 was crossed to tomato (L. esculentum) and the F1 was backcrossed to tomato. Self-pollinated seed was saved from backcross plants and seedlings derived were inoculated with Fusarium oxysporum Schlecht f.sp. radicus-lycopersici Jarvis and Shoemaker, the causal agent of Fusarium crown and root rot (FCRR). Seed was saved from resistant plants that were self-pollinated and screened until homozygous resistance was verified five generations after the backcross. Three homozygous lines were crossed to Fla. 7547, a tomato breeding line susceptible to FCRR but resistant to Fusarium wilt races 1, 2, and 3. Subsequently, backcrosses were made to each parent and F2 seed were obtained. The three homozygous FCRR-resistant lines were also crossed to Ohio 89-1, which has a dominant gene for FCRR resistance presently being used in breeding programs. F2 seed were obtained from these crosses. These generations were inoculated with the FCRR pathogen. The resistant parents, F1, and backcross to the resistant parents were all healthy. The backcross to the susceptible parent and the F2 segregated healthy to susceptible plants in 1:1 and 3:1 ratios, respectively. Thus, the resistance from LA 1277 was inherited as a single dominant gene. This gene was different than the gene from Ohio 89-1 because susceptible segregants were detected in the F2 generation derived from the two resistant sources.

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Susan L. Eggleston, Darlene M. Lawson, and Martha A. Mutschler

Acylsugars produced by many accessions of wild tomato (L. pennellii) mediate resistance to a number of important pests of tomato. The highly resistant L. pennellii accession LA716 accumulates high levels of acylsugars, of which 85% are in the form of acylglucoses, the rest being acylsucroses. In contrast, L. pennellii accession LA1912, which does not show the insect resistance of accession LA716, accumulates very low levels of acylsugars, of which 55% are represented by acylglucoses. The intraspecific F1 derived from crosses between the accessions LA716 and LA1912 accumulates moderate levels of acylsugars, of which, like its LA716 parent, 85% are in the form of acylglucoses. Intraspecific F2 and backcross populations derived from crosses between the accessions LA716 and LA1912 were surveyed for acylsucrose and acylglucose production. These populations segregated for the ability to produce acylsugars, levels of total acylsugars produced and amount of acylglucoses as a percentage of total acylsugars. The genetic control of these traits will be discussed.

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Y. Saranga, D. Zamir, A. Marani, and J. Rudich

Abbreviations: acc., accessions; ECe, electrical conductivity of saturated soil extract; ECi, electrical conductivity of irrigation water; Lc, Lycopersicon cheesmanii ; Le, Lycopersicon esculentum ; Lpen, Lycopersicon pennellii ; Lper

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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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M.R. Foolad and G.Y. Lin

Seed of 42 wild accessions (Plant Introductions) of Lycopersicon pimpinellifolium Jusl., 11 cultigens (cultivated accessions) of L. esculentum Mill., and three control genotypes [LA716 (a salt-tolerant wild accession of L. pennellii Corr.), PI 174263 (a salt-tolerant cultigen), and UCT5 (a salt-sensitive breeding line)] were evaluated for germination in either 0 mm (control) or 100 mm synthetic sea salt (SSS, Na+/Ca2+ molar ratio equal to 5). Germination time increased in response to salt-stress in all genotypes, however, genotypic variation was observed. One accession of L. pimpinellifolium, LA1578, germinated as rapidly as LA716, and both germinated more rapidly than any other genotype under salt-stress. Ten accessions of L. pimpinellifolium germinated more rapidly than PI 174263 and 35 accessions germinated more rapidly than UCT5 under salt-stress. The results indicate a strong genetic potential for salt tolerance during germination within L. pimpinellifolium. Across genotypes, germination under salt-stress was positively correlated (r = 0.62, P < 0.01) with germination in the control treatment. The stability of germination response at diverse salt-stress levels was determined by evaluating germination of a subset of wild, cultivated accessions and the three control genotypes at 75, 150, and 200 mm SSS. Seeds that germinated rapidly at 75 mm also germinated rapidly at 150 mm salt. A strong correlation (r = 0.90, P < 0.01) existed between the speed of germination at these two salt-stress levels. At 200 mm salt, most accessions (76%) did not reach 50% germination by 38 days, demonstrating limited genetic potential within Lycopersicon for salt tolerance during germination at this high salinity.

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Y. Saranga, D. Zamir, A. Marani, and J. Rudich

Abbreviations: ECi, electrical conductivities; Lc, Lycopersicon cheesmanii; Le, Lypopersicon esculentum; Lpen, Lycopersicon pennellii; Lper, Lycopersicon peruvianum; TD, total dry matter. 1 Deceased May 1986. This research was conducted within

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Yuan-Hai Zhang and Lyle E. Craker

Air pollution may play a role in gametophytic selection. To estimate whether such selection was occurring, pollen grains from homozygous and heterozygous tomato plants were tested under pollution stress. Homozygous pollen could be expected to respond to pollution more uniformly than heterozygous due to the identical genotype of the pollen grains. Acid rain reduced pollen germination and tube elongation in Lycopersicon hirsutum LA1777 (heterozygous) and Lycopersicon pennellii LA716 (nearly homozygous). UV-B reduced tube length of the pollen from both plants, but ozone only reduced pollen tube length of L. pennellii. The responses of these two kinds of pollen to acid rain, ozone, and UV-B appears to be same in terms of heterozygosity and stress dosages, suggesting the reduction of pollen germination and tube elongation under pollution stress may be mediated through physiological or physical alterations and not a response of different genotypes.