Date of Award
Master of Science (MS)
Plant and Environmental Science
Dr. Ksenija Gasic
Dr. Juan Carlos Melgar
Dr. Christopher Saski
Climate change is affecting the production of temperate fruit crops, with cold temperatures emerging as a critical abiotic stressor that limits plant growth and performance. Freeze damage, particularly in spring, has resulted in significant economic losses in peach production in the southeastern United States. Research efforts in peach and other Prunus species have primarily focused on studying dormancy-related traits associated with bloom time, such as chill and heat requirement, with fruitlet freeze tolerance not equally represented. Breeding for climate resilience in peach requires a combination of these traits to allow for late bloom via targeted chill requirement and high heat requirement, and fruitlet tolerance to late spring frosts (LSF). This study assessed fruitlet freeze tolerance in 75 peach and nectarine accessions representing modern peach breeding germplasm. Fruitlet freeze tolerance was assessed at six freezing temperatures (0 to -10ºC) using electrolyte leakage method over two seasons (2022-20223). The fruitlet freeze was described as the temperature at which 50% of tissue experiences damage, LT50 or inflection point (IP), determined from the asymmetric sigmoid curve, and as an area under the curve (AUC). The IP ranged from -3.94 °C to -10.22 °C and AUC ranged from 16-48%, with lower AUC suggesting higher tolerance. The majority of the accessions demonstrated tolerance to cold temperatures in the -4 to -6ºC LT50 and 25-35% AUC range. However, variability in tolerance was noted across different years, as well as some inconsistencies between the index of performance (IP) and AUC measurements. When categorizing accessions into tolerance groups (TGs), more stability was seen with AUC grouping across the study years. Shifts in TG assignments were also observed, particularly among extreme categories, where some accessions moved from the most tolerant (TG1 and TG3) to an intermediate tolerance group (TG2) in subsequent experimental years. A set of seven and nine nectarines were classified as most tolerant in both seasons, 2022 and 2023, using both IP and AUC, respectively. Broad-sense heritability (H2) estimates of 0.52 and 0.80, for IP and AUC, respectively, suggested genetic control of this trait with a potential for improvement via breeding. Further research into the genetic determinants of freeze tolerance in peach fruitlets was conducted using genome-wide association studies. We identified seven significant associations between genetic markers and the trait across four chromosomes of the peach genome. Candidate gene analyses identified 144 genes in the 100kb flanking region of each significantly associated SNP marker located on Ch2 (53), Ch5 (13), Ch6 (26), and Ch7 (51). op Additional research is required to further investigate candidate genes.
The results of this study demonstrated genetic control of fruitlet freeze tolerance in peach and revealed multiple genomic regions associated with the inheritance of this trait, thus providing a foundation for breeding climate-resilient varieties. These findings support the feasibility of incorporating fruitlet freeze tolerance in climate resilience breeding for sustainable production in a changing climate.
Caglar, Ufuk, "Enabling Breeding for Fruitlet Freeze Tolerance in Peach" (2023). All Theses. 4174.