Graduate Thesis Or Dissertation
 

Breeding tomato for increased fruit phenolics

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  • The purpose of this research was to develop tools and germplasm for the production of tomatoes (Solanum lycopersicum L.) with high fruit phenolics without the use of genetic engineering. A candidate gene analysis was undertaken to identify genes regulating anthocyanin biosynthesis in tomato fruit (Aft, Abg, atv, and Purple Smudge). The genes Aft and Purple Smudge were associated with a DNA polymorphism in a tomato MYB transcription factor (SlAn2) similar to Petunia An2. The SlAn2 DNA polymorphism co-segregated with the Aft trait in 183 F2 individuals from an Aft x ‘Legend’ population. Expression analysis of the SlAn2 gene using semi-quantitative reverse transcription PCR showed a close correlation between transcript levels of SlAn2, anthocyanin expression, and the anthocyanin biosynthetic gene dihydroflavonol 4-reductase (DFR). Expression analysis of the related MYB transcription factor SlAnt1 showed poor correlation with anthocyanin expression in the fruit. The SlAn2 gene was sequenced in several genotypes. Phylogenetic analysis of the predicted amino acid sequences of tomato SlAnt1 and SlAn2 indicated that they are orthologous to potato StAn1 and StAn2, respectively. To create a high flavonol tomato line, an elite high anthocyanin line with the genes Aft and atv was crossed to a tomato line with the aw gene, which encodes a non-functional DFR. AftAft/atvatv/awaw F3 segregants had fruit with levels of rutin and chlorogenic acid that were significantly higher than the cultivar ‘Legend’ fruit under greenhouse conditions. Total phenolics levels in fruit of AftAft/atvatv/awaw F3 segregants were not significantly different from an elite AftAft/atvatv line under field conditions. However, small amounts of anthocyanin were unexpectedly found in fruit. In order to identify and introgress additional genes that would increase total phenolics or result in novel phenolic compounds in tomato fruit, we screened a core collection of Solanum lycopersicum var. cerasiforme, and identified several accessions with good horticultural quality and fruit with significantly higher levels of total phenolics and polyphenolic compounds not found in cultivated tomatoes.
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