Location: Innovative Fruit Production, Improvement, and Protection
2018 Annual Report
Objectives
Objective 1: Develop elite breeding parents for apple containing both disease resistance alleles to blue mold, apple scab, and fire blight, and desirable fruit quality alleles using rapid cycle breeding technology. [NP301, C1, PS1B]
Objective 2: Utilize Malus sieversii (an apple progenitor species) and a forward overexpressing system (FOX-hunting) to identify and functionally analyze apple genes conferring disease and environmental stress resistance. [NP301, C3, PS3A]
Objective 3: Utilize CRISPR technology to improve disease resistance or environmental stress tolerance in 'Royal Gala'. [NP301, C1, PS1B]
Approach
Environmental stress and outbreaks of disease can severely reduce apple fruit production. New cultivars with improved stress and disease resistance will be needed in order for the U.S. apple industry to remain competitive. Rapid cycle breeding will be used to combine multiple disease resistance alleles for fire blight, apple scab and blue mold resistance within genetic backgrounds that are suitable for use in apple breeding programs. DNA-informed breeding methods, rather than conventional phenotyping methods, will be used to predict individuals with multiple sources of disease resistance and fruit quality traits. The wild apple species, Malus sieversii, is considered to represent a reservoir of disease and stress resistance genes, as well as a source of novel, quality traits (flavour, texture, etc.). A Full-length cDNA Over-eXpressing (FOX) Gene Hunting system will be used to conduct high-throughput screening of genes in Malus sieversii – PI613981 (disease and drought tolerant elite genotype) that are associated with freezing, drought, and salt tolerance. Once vetted, the identified genes will be used to produce apple genotypes of ‘Royal Gala’ with improved stress tolerance. Lastly, several potential genes regulating time of bud break will be characterized in transgenic and non-transgenic apple lines to confirm their role in the regulation of bud break. Key regulatory motifs in the promoters of these genes will be modified using CRISPR/Cas9 technology to produce genotypes with delayed bud break in order to adapt apple genotypes to erratic spring weather patterns.
Progress Report
A critical aspect of the planned research is to use the rapid cycling breeding system in apple to validate disease resistance markers and to introgress non-domesticated germplasm carrying novel traits with domesticated germplasm to remove the low-quality genetic background. Crosses between reduced juvenility apple lines and blue mold resistant genotypes were made and seed was collected, stratified, and planted. Plants carrying the reduced juvenility gene were planted and pollinated with pollen from an 'Enterprise' parent. The resulting fruit is being evaluated for blue mold resistance and the presence of blue mold resistance markers. This will validate the blue mold resistance markers and begin the process of incorporating the resistance into a higher quality genetic background. Validation of the blue mold resistance markers and the incorporation of blue mold resistance into a better genetic background will provide a novel resource to apple breeders and prevent the need to treat apple fruit with fungicides to control the disease.
To develop elite breeding parents for apple containing both disease resistance and desirable fruit quality alleles crosses were made between ‘Pinova’ seedlings over-expressing BpMADS4 gene for an early flowering phenotype and Malus sieversii PI 613981 progeny, ‘Honeycrisp’ and disease resistant ‘Enterprise’. Using DNA-informed breeding methods progeny were selected that were early flowering and contained disease resistance and fruit quality alleles. Subsequent crosses will be made using rapid cycle breeding to pyramid and combine alleles for blue mold, fire blight and scab resistance.
Maintenance of dormancy through early spring frosts would reduce losses faced by growers. Several bud break-related genes have been identified in apple. Apple trees over expressing the two apple versions of the EBB (Early Bud Break) gene have been created along with trees over expressing the Popt (poplar) EBB1 and Prup (peach) EBB1 genes. The MdEBB1 and PoptEBB1 lines are currently undergoing greenhouse evaluations while the MdEBB1 and PrupEBB1 lines are being selected.
Accomplishments
