Investigations of trait relationships in fruit rot resistant and low acid american cranberry (vaccinium macrocarpon ait.) populations
Creators: name: Knowles, Sara
Publisher: name: No Publisher Supplied
Year: 2025

description: American cranberry (Vaccinium macrocarpon Ait.) is an economically important crop severely affected by fruit rot, a disease complex including up to 15 fungal pathogen species. In Chapter 2 of this thesis, a mapping population (n = 219) bred with high yielding parentage and three diverse sources of fruit rot resistance (FRR) was evaluated under fruit rot pressure for fruit quality traits: percent rotted fruit, yield, berry size, titratable acidity (TA), soluble solids (brix), total anthocyanin content (TAcy), citric, malic, quinic, and benzoic acids. The purpose of this study was to evaluate the relationships with FRR and horticultural traits. Significant genetic variation in the mapping populations was observed for all traits, with percent rotted fruit ranging from 7.5 - 76.6%, yield ranging 11.9 - 201.8 g/0.09 m2 and TA ranging 1.70 - 2.42% across three beds (locations) and years (2019 - 2021). High yielding, low fruit rot selections were identified. A promising selection had an adjusted mean yield of 201.8 g/0.09 m2 and 23.0% rotted fruit, showing an improvement over both parents and the population mean. Percent rotted fruit did not significantly correlate with yield or fruit weight, suggesting low to no linkage between these fruit quality traits and FRR. However, there was a moderate positive correlation between FRR and TA, and FRR and quinic acid, suggesting potential acid-tolerance of some pathogenic fungi involved in the disease complex. A moderate negative correlation was found between percent rotted fruit and benzoic acid concentration, providing further evidence for the phytochemical’s role in FRR. Additionally, quantitative trait loci were detected for percent rotted fruit, fruit weight, brix, TA, malic, citric, and benzoic acids. Cranberries contain high concentrations of organic acids (such as malic and citric acids) when compared to other fruit (e.g. blueberry, apple, and grape), requiring addition of sugars to make the marketed products palatable, which can deter health-conscious consumers. Breeding cranberry fruit for lower acidity may help consumer acceptance in perceiving a “sweeter” product. Leaf morphology affects photosynthetic capacity, which can alter metabolomic profiles and fruit acidity. Chapter 3 of this thesis characterizes leaf and fruit morphology, fruit weight, TA, brix, and concentrations of malic, citric, quinic, and benzoic acids, and explores relationships of these traits in a full-sibling low acid population segregating for a unique leaf and fruit shape (n = 64). Phenotypes were measured over two years (2021-2022) from plants growing in the greenhouse. Fruit shape was visually assessed and grouped into two categories: (1) ellipsoidal and (2) oblate. For leaves, leaf aspect ratios (LARs; length/width ratio) and Feret’s diameter were quantified using a flatbed scanner and the ImageJ macro “MuLES”. LAR was significantly correlated with fruit weight (R2 = 0.65) and TA (R2 = 0.29). In the oblate-shaped fruit group, leaves had lower LARs (p = 4.7e-15) and their fruit had lower TA (p = 4.0e-3). Additionally, the oblate fruit shape group had lower leaf Feret’s diameter than the ellipsoidal group’s leaves (p = 9.1e-05). The fruit shape groups also differed in fruit weight, with the oblate group having a lower fruit weight than the ellipsoidal group (p = 4.2e-6). These results suggest links between leaf shape parameters, fruit weight, fruit chemistry, and flowering time in this low acid cranberry population. Understanding the relationships between these traits has the potential to inform scientists with any correlated traits across plant organs. Examination into organic acid profiles in leaves of this population and similar populations will improve our understanding of the connections between organ morphology and cranberry chemistry.