Elucidation of the extended pedigree of ‘Honeycrisp’ apple and genetic architecture of its susceptibility to soft scald and soggy breakdown postharvest fruit disorders and zonal leaf chlorosis disorder

Abstract

The apple (Malus × domestica) cultivar Honeycrisp has become important economically and as a breeding parent due to its ultra-crisp fruit texture, its ability to retain this high level of fruit crispness in storage, and its resistance to apple scab. However, ‘Honeycrisp’ has several detrimental traits that have not been satisfactorily evaluated genetically. Additionally, the original pedigree records for ‘Honeycrisp’ were previously determined as incorrect and this lack of pedigree information has impeded thorough genetic analyses in studies involving ‘Honeycrisp’. The objectives of the research in my dissertation were to identify and genetically describe the parents and grandparents of ‘Honeycrisp’ and to use this new pedigree information in pedigree-based analyses to examine the genetic architecture of its susceptibility to fruit soft scald and soggy breakdown postharvest fruit disorders and zonal leaf chlorosis disorder. Towards these objectives, a high quality genetic map was created using single nucleotide polymorphism data from the apple 8K Illumina Infinium® SNP array and five large families with ‘Honeycrisp’ as a common parent. ‘Keepsake’ was verified as one parent of ‘Honeycrisp’ and ‘Duchess of Oldenburg’ and ‘Golden Delicious’ were identified as grandparents through a previously unknown parent that was identified to be the University of Minnesota selection MN1627. Two quantitative trait loci (QTL) were consistently identified on linkage groups (LGs) 2 and 16 for both soft scald and soggy breakdown. ‘Honeycrisp’ is homozygous for an identical by state haplotype identified at the LG2 QTL that was consistently associated with increased incidences of soft scald and soggy breakdown. ‘Honeycrisp’ inherited the deleterious haplotypes at the LG2 QTL from grandparent ‘Keepsake’ and great-grandparent ‘Grimes Golden’. A large effect QTL for zonal leaf chlorosis was identified on LG9 and a recombinant haplotype that ‘Honeycrisp’ inherited from ‘Duchess of Oldenburg’ at this QTL was associated with increased ZLC in offspring of ‘Honeycrisp’. The LG9 QTL was located approximately between 5 and 10 cM away from a major QTL for skin over color. ‘Honeycrisp’ is heterozygous for skin over color at this location. In ‘Honeycrisp’, the haplotype associated with increased zonal leaf chlorosis at the LG9 QTL is in coupling phase with the haplotype associated with red color at the LG9 skin over color QTL. All of these major QTL were consistently identified across all years of analysis. These new discoveries will be useful in apple breeding efforts involving ‘Honeycrisp’, its ancestors, and its progeny.