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Colleen Kennedy, Tomas N. Hasing and Vance M. Whitaker

Wild Fragaria supercore accessions from the U.S. Department of Agriculture (USDA) National Plant Germplasm System collection have been evaluated in temperate climates; however, there have been no characterizations of supercore accessions in non-temperate climates or in annualized production systems. Because Florida can serve as a model system for annualized winter and spring production worldwide, the objective of this study was to characterize an elite group of wild strawberry accessions under field and high tunnel production systems for mortality and the phenological responses of flowering and runner production. The wild accessions along with cultivars were planted in open-field and high tunnel production environments in a randomized complete block design within each environment with raised beds serving as blocks. Four replications of five-plant plots were planted in each of two environments in 2 separate years. With the exception of Darrow 72, F. chiloensis accessions did not perform well in the minimum-chill annualized winter production system. The accessions of this species generally did not flower and were prolific instead in runner production. The F. virginiana accessions performed better with F. virginiana subsps. grayana and virginiana accessions appearing more adapted for minimum-chill winter production because they flowered well and had few runners. We conclude that NC 96-48-1 (PI 612324), NC 95-21-1 (PI 612569), Darrow 72 (PI 236579), and RH 30 (PI 612499) would be attractive for inclusion in germplasm development in a minimal-chill, winter annual production system. In addition to producing many flowers and few runners, these accessions had low mortality.

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Tomas N. Hasing, Luis F. Osorio and Vance M. Whitaker

Previous studies have recognized considerable variation in the soluble solids content (SSC) of strawberries (Fragaria ×ananassa) during Florida’s fruiting season. Cultivars with stable fruit SSC over time would be valued in the commercial industry as a result of their more uniform quality. The within-season stability of 410 genotypes from the strawberry breeding program of the University of Florida was estimated using data from clonally replicated first-year seedlings and advanced selections evaluated at two locations over two consecutive seasons. Stability was measured using a linear regression approach. For each genotype, the SSC measured at different harvest dates was regressed on the mean SSC of an independent set of genotypes at each harvest date. Genotypes with steep slopes are sensitive to small environmental and physiological changes and are considered unstable compared with genotypes with slopes close to zero. Approximately 90% of individual genotype slopes were not different from the population slope value and were classified in the average stability group, whereas the remaining 10% were equally distributed between the unstable and stable groups. Although a preliminary genetic analysis indicated that SSC stability may have low narrow-sense heritability (h 2 = 0.06 ± 0.05), a group of genotypes exhibited stability across multiple environments. Soluble solids content stability and mean soluble solids were independent, and genotypes with both stable and high levels of SSC were observed.

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Colleen Kennedy, Tomas N. Hasing, Natalia A. Peres and Vance M. Whitaker

Many breeders have turned to wild relatives in search of beneficial traits such as disease resistance. In strawberry, the wild octoploid species Fragaria virginiana and F. chiloensis are fully interfertile with the cultivated species, F. ×ananassa, and are therefore potential sources of resistance. Powdery mildew may increase in economic importance in Florida in the near future as a result of the use of high tunnels and rowcovers for freeze protection, which limit free water and provide a favorable environment for disease development. The objective of this study was to screen an elite group of wild strawberry accessions for resistance to powdery mildew under two production systems. In 2010–11 and 2012–13, wild accessions, commercial standard cultivars, and susceptible controls were planted in open-field and high tunnel environments at the Gulf Coast Research and Education Center in Balm, FL. Although there was a significant year × genotype effect, some taxa showed high levels of resistance that were consistent across years. There was a high correlation for ratings of powdery mildew between the high tunnel and the open field for all genotypes (r = 0.89, P < 0.001). This information may be useful for breeders, because sources of resistance to powdery mildew are available within the tested genotypes. However, some accessions are highly susceptible to powdery mildew, and this must be considered when using these genotypes in breeding programs.