Net photosynthesis (Pn) and photosynthate partitioning were compared between fruiting and deblossomed strawberry plants. Throughout a six-week fruiting cycle, Pn (leaf area basis), specific leaf weight (SLW), and chlorophyll content were determined at 7-day intervals for an early-formed leaf (old leaf) and for the most recently expanded leaf (young leaf) of fruiting and deblossomed day-neutral plants (cv. Tribute). During the fifth week of the fruiting cycle, Pn of the young leaf was higher for fruiting plants than for deblossomed plants. Pn of the old leaf was not different between treatments during any week. During weeks 4 and 5, the young leaf of the deblossomed plants had a higher SLW than that of fruiting plants; SLW of the old leaf was higher for deblossomed plants during weeks 4-6. The young leaf of the deblossomed plants had a higher chlorophyll content than that of fruiting plants during weeks 1 and 4. Chlorophyll content of the old leaf was higher for deblossomed plants during weeks 1, 2, and 4. There were no differences between treatments for stomatal conductance for CO₂ or dark respiration during any week of the fruiting cycle. In another experiment, deblossoming day-neutral strawberry plants (cv. Tribute) increased the amount of ¹⁴C translocated to the newly-emerging leaves 48 hrs after treatment with ¹⁴CO₂. During weeks 3-6 of the fruiting cycle, leaves of deblossomed plants had a greater total area, dry weight, and total non-structural carbohydrate (TNSC) content than leaves of fruiting plants. Pn on a whole-plant basis was higher for deblossomed plants than fruiting plants. This was largely due to the greater leaf area of the deblossomed plants, since total leaf area was highly correlated with Pn (whole plant basis). Pn (whole plant basis) was highly correlated with total dry weight and TNSC of plants in both treatments. Thus, deblossoming changed Pn and dry matter partitioning of strawberry plants. The additional leaf area and greater Pn rates (whole plant basis) obtained by deblossoming strawberry plants may result in increased yields during subsequent fruiting cycles. / Ph. D.

Indiana University-Purdue University Indianapolis (IUPUI) / Winter survival is variable among commercially grown strawberry (Fragaria x ananassa) cultivars. The main objectives of this study were to evaluate the molecular basis that contribute to this difference in strawberry cultivars and to identify potential biomarkers that can be used to facilitate the development of new strawberry cultivars with improved overwintering hardiness. With these goals in mind, the freezing tolerance was examined for four cultivars, ‘Jonsok’, ‘Senga Sengana’, ‘Elsanta’, and ‘Frida’ (listed from most to least freezing tolerant based on survival from physiological freezing experiments) and the protein expression was investigated in the overwintering relevant crown structure of strawberry. Biomarker selection was based on comparing the protein profiles from the most cold-tolerant cultivar, ‘Jonsok’ with the least cold-tolerant cultivar ‘Frida’ in a comprehensive investigation using two label-free global proteomic methods, shotgun and two dimensional electrophoresis, with support from univariate and multivariate analysis. A total of 143 proteins from shotgun and 64 proteins from 2DE analysis were identified as significantly differentially expressed between ‘Jonsok’ and ‘Frida’ at one or more time points during the cold treatment (0, 2, and 42 days at 2 ºC). These proteins included molecular chaperones, antioxidants/detoxifying enzymes, metabolic enzymes, pathogenesis related proteins and flavonoid pathway proteins. The proteins that contributed to the greatest differences between ‘Jonsok’ and ‘Frida’ are candidates for biomarker development. The novel and significant aspects of this work include the first crown proteome 2DE map with general characteristics of the strawberry crown proteome, a list of potential biomarkers to facilitate the development of new strawberry cultivars with improved cold stress tolerance.