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theses

American cranberry (Vaccinium macrocarpon Ait.) fruit are renowned for two traits; extreme sourness and their abundance of health-promoting compounds. Extreme sourness in cranberry fruit is due to the high levels of malic, citric, and quinic acids, which together contribute to titratable acidity (TA). Commercially grown cranberries have a TA of 2.3-3.0%, well over two times the amount in most edible fruits. Thus, considerable amounts of ‘added-sugar’ are necessary for palatability. In addition to citric, malic, and quinic acids, cranberry fruit also have high levels benzoic acid. While benzoic acid does not statistically contribute to TA, but has health promoting benefits.
To ascertain the variation found in organic acids in existing breeding populations, four bi-parental crosses were phenotyped for malic, citric, quinic, and benzoic acids. Generally, the four organic acids displayed transgressive segregation to the parents. Genotyping by sequencing (GBS) was then used to map genetic diversity within the populations. A total of 61 QTLs were identified for the four organic acids.
In addition to the variation in organic acids in breeding populations, there were two accessions with unique genotypes from the germplasm collection with significantly lower citric acid (≈ 2 mg/g) (cita) and malic acid (≈ 2 mg/g) (mala). A series of crosses utilizing these accessions revealed that cita and mala are independently segregating Mendelian loci. A bulked segregant approach with simple sequence repeats (SSRs), then a QTL identification approach with single nucleotide polymorphisms (SNPs) generated through GBS was used to fine map these two traits. Two SSR markers and one SNP marker were identified for the cita locus while two SNP markers were identified for the mala locus.
The cita trait had multiple alleles contributing to differential levels of citric acid concentrations depending on the parent, e.g. Stevens or #35. Both the cita and mala traits exhibit partial dominance. In two dihybrid crosses with both cita and mala, an epistatic effect was between these two traits. There was a significant effect of the cita alleles on increasing malic acid concentration while the presence of mala alleles reduced both citric and malic acid concentrations. This work determined the inheritance and variation of organic acids as well as developed molecular markers linked with low citric and low malic acid traits. These markers will be used for marker assisted selection to accelerate the breeding process of cranberry.

ETD_9864

Ph.D.

Includes bibliographical references

doi:10.7282/t3-gve8-s939

ETD doctoral

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