Phenology, chilling requirements, and disease resistance in hybrid hazelnut
Creators: name: Hlubik, David J.
Publisher: name: No Publisher Supplied
Year: 2024

description: Hazelnut (Corylus spp.) is a major worldwide tree nut crop with production centered in regions with Mediterranean climates. European Hazelnut (Corylus avellana) is the main species for commercial production due to its favorable nut characteristics. Despite rising demand, expansion to new growing regions is challenged by factors including susceptibility to the fungal pathogen Anisogramma anomala and cold tolerance of C. avellana germplasm. Anisogramma anomala is the causal organism of the disease eastern filbert blight (EFB) and is endemic to the eastern United States. It is harbored on the wild American Hazelnut (C. americana), causing few disease symptoms, but is devastating to nearly all C. avellana trees. While EFB can be controlled with fungicides, genetic resistance is the preferred method for long term disease management to keep crop inputs low. In recent years, the breakdown of single gene sources of EFB resistance have demonstrated the need for durable, horizontal resistance such as found in C. americana. In addition to disease resistance, C. americana germplasm contains other favorable traits including cold tolerance and later flowering/budbreak time, both of which are beneficial to the expansion of hazelnut into new colder growing regions. Like other temperate fruit and nut crops, hazelnuts rely on the accumulation of chilling to maintain dormancy followed by warm temperatures for flowering and budbreak in the spring. A major goal of this work was to quantify both chilling and heating requirements of hazelnuts to better predict their responses in new growing regions and longer-term responses in regard to climate change. Additionally, three mapping populations were phenotyped for time of flowering and budbreak and a QTL analysis was performed for these traits. Lastly, 62 C. americana seedlots, 22 F1 hybrid (C. americana x C. avellana) progenies, 38 clonal F1 selections, and 26 F2 progenies were evaluated for resistance/tolerance to EFB. Chilling requirements in C. avellana, C. americana, and interspecific hybrids ranged from 9.3 to 30.7 CP for catkins, 10.5 to 44.0 CP for female flowers, and 28.5 to 51.0 CP for vegetative buds. Growing degree hour requirements ranged from 6,240 to 11,140 GDH for catkins, 3,644 to 8,336 GDH for female flowers, and 5,447 to 13,629 GDH for vegetative buds. Analysis suggested that bloom date may be 5 to 28 days earlier with impending climate change, suggesting breeding for higher GDH requirements may be a solution to avoid bloom during cold temperatures. 24 QTL’s for phenology traits were found between the three mapping populations, including five for date of vegetative budbreak, eight for date of female flowering, six for date of pollen shed, and five for heterodichogamy. A major QTL on linkage group 2 was associated with all four phenology traits. The first QTLs for phenology in C. americana were discovered on linkage groups 2, 3, and 11. C. americana demonstrated durable resistance, with seedlots averaging an EFB rating of 0.31 after ten years of disease exposure. F1 progenies observed during the same period were much more variable, with EFB progeny means ranging from 1.95 to 4.98 and averaging 3.98. F1 breeding selection EFB genotype means ranged from 0.33 to 5.00, representing percent diseased wood of 0.04% to 40.92%. F2 progenies demonstrated transgressive segregation, with progeny means ranging from 0.67 to 4.92 and averaging 2.85. Narrow sense heritability of EFB resistance was estimated at 0.64. In summary, this body of work demonstrates that integration of C. americana germplasm into the breeding program could be beneficial, particularly when dealing with the high disease pressure and colder climate of the eastern United States and offers insight into expansion of hazelnut growing regions also facing these challenges.