Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Plant and Soil Sciences

First Advisor

Dr. John C. Snyder

Abstract

Tomato (Solanum lycopersicum) is one of the most economically important vegetable crops grown around globe but is a host for numerous pests and pathogens. In the future, tomato breeders will have to focus on increasing fruit quantity and on enhancing pest resistance. Many accessions of the wild relative of tomato, S. habrochaites display high levels of resistance towards arthropods such as spider mites. The presence of the sesquiterpene hydrocarbon, 7-epi-zingiberene, found in S. habrochaites type IV trichomes has been associated with arthropod resistance. However, the presence of other compounds in its trichome secretions may also be related to arthropod resistance. One goal of this research was to evaluate the potential for using a spectrophotometer to enable accurate selection for 7-epi-zingiberene content by breeders. Another objective was to identify and evaluate the relative antixenotic activities on spider mites of major components present in the trichome secretions of a wild tomato. The third objective was to evaluate yield, 7-epi-zingiberene content and fruit nutrient quality in advanced interspecific hybrid lines to demonstrate that high yield and high zingiberene content have been successfully combined, and also to evaluate nutritional aspects of fruit quality of these hybrids such as phenolic content, lycopene, soluble solids, and ascorbic acid. Results for the first objective included identification of two novel compounds present in wild tomato trichome secretions as hydroxy-zingiberene and 9-hydroxy-10,11-epoxy-zingiberene. The spider mite repellency of each of these compounds was at least five times greater than that of 7-epi-zingiberene. The results for objective two showed that a spectrophotometer could be a very valuable tool for aiding selection of plants having high levels of 7-epi-zingiberene on their leaves and having low levels of other compounds such as monoterpenes, which are present on arthropod –susceptible tomato plants. Completion of the third objective indicated that high yield has been successfully combined with high 7-epi-zingiberene concentration and that the nutritional value of the fruit in the hybrids is at least equal to the recurrent parent and in some cases, the interspecific hybrids may be useful for improving tomato fruit nutritional content including: phenolics, lycopene, soluble solids, and ascorbic acid. In general, the phenolic content of interspecific hybrid tomatoes ranged from 325 to 427 μg/g fresh fruit, lycopene content ranged from 31 to 66 μg/g and soluble solids ranged from 4 to 7.8%, whereas those characteristics were lower in cultivated tomato hybrids. Ascorbic acid typically ranged between 483 and 498 μg/g fresh fruit in interspecific hybrids and was higher than that in cultivated tomato hybrids (337 μg/g). For future prospects, it may be possible to breed genotypes that have high yield, have improved nutritional value and are also resistant to arthropod pests.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.090

Available for download on Wednesday, April 28, 2021

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