Blueberry ( Vaccinium corymbosum and hybrids) is an autotetraploid crop whose commercial relevance has been growing steadily during the last 20 years. However, the ever-increasing cost of labor for hand-picking blueberry is one main constraint in competitive marketing of the fruit. Machine harvestability is, therefore, a key trait for the blueberry industry. Understanding the genetic architecture of traits related to machine harvestability through Quantitative Trait Loci (QTL) mapping is the first step toward implementation of molecular breeding for faster genetic gains. Despite recent advances in software development for autotetraploid genetic mapping, a high-resolution map is still not available for blueberry. In this study, we crafted a map for autotetraploid low-chill highbush blueberry containing 11,292 SNP markers and a total size of 1,953.97 cM (average density of 5.78 markers/cM). This map was subsequently used to perform QTL analyses in 2-year field trials for a trait crucial to machine harvesting: fruit firmness. Preliminary insights were also sought for single evaluations of firmness retention after cold storage, and fruit detachment force traits. Significant QTL peaks were identified for all the traits and overlapping QTL intervals were detected for firmness across the years. We found low-to-moderate QTL effects explaining the phenotypic variance, which suggest a quantitative nature of these traits. The QTL intervals were further speculated for putative gene repertoire. Altogether, our findings provide the basis for future fine-mapping and molecular breeding efforts for machine harvesting in blueberry.

Bermudagrass (Cynodon spp.) is a forage and turf crop commonly used worldwide. The USDA bermudagrass germplasm set is composed of plant introductions (PI’s) collected around the world and contains different Cynodon species, primarily C. dactylon. The collection was screened in a replicated trial in Florida for forage yield, leaf width, nutritive value (NV), and Bermudagrass Stem Maggot (Atherigona reversura) (BSM), which is an invasive pest to the southeastern United States that damages bermudagrass fields. The goal of this research was to determine ploidy level and genome size in this USDA collection, and evaluate the influence of ploidy level in the estimation of genetic parameters for BSM, leaf width, dry matter yield, and NV traits. For chromosome counts using classical cytogenetics techniques, root tips and meristems were collected from a set of PI’s with known ploidy. The PI’s and cultivars with known chromosome counts were used as internal standards to run flow cytometry and estimate genome size of the PI’s with unknown ploidy. Ploidy level was determined for all accessions and were used to estimate genetic parameters of phenotypic traits. By providing information on ploidy levels and genetic parameters, this research will support breeding efforts and future selections for forage bermudagrass.

2Blueberry (Vacciunium corymbosum and hybrids) is an autotetraploid crop whose commercial 3 relevance has been growing steadily during the last twenty years. However, the ever-increasing 4 cost of labor for hand-picking blueberry is one main constraint in competitive marketing of the 5 fruit. Machine harvestability is, therefore, a key trait for the blueberry industry. Understanding 6 the genetic architecture of traits through quantitative trait locus (QTL) mapping is the first step 7 towards implementation of molecular breeding for faster genetic gains. Despite recent advances 8 in software development for autotetraploid genetic mapping, a high-resolution map is still not 9 available for blueberry. In this study, we crafted a map for autotetraploid low-chill highbush 10 blueberry containing 11,292 SNP markers and a total size of 1,953.97 cM (average density of 11 5.78 markers/cM). This map was subsequently used to perform QTL analyses for traits relevant 12 to machine harvesting: firmness, firmness retention, and fruit detachment force. Significant 13 QTL peaks were identified for all the traits. The QTL intervals were further explored for putative 14 candidate genes. Genes related to cell wall remodeling were highlighted in the firmness and 15 firmness retention intervals. For fruit detachment force, transcription factors involved in fruit 16 abscission were detected. Altogether, our findings provide the basis for future fine-mapping and 17 molecular breeding efforts for machine harvesting in blueberry. 18 Keywords: Vaccinium, southern highbush blueberry, firmness, detachment force, polyploid 19 20chromosomal alterations are not only tolerated by plant genomes, but can also drive evolution, for example, 21 promoting speciation (Adams and Wendel, 2005). Polyploid organisms are classified as either allopolyploids 22 or autopolyploids, depending on the degree of divergence between their subgenomes (Brubaker et al., 1999). 23 Autopolyploids, such as blueberry (Vaccinium corymbosum L.), potato (Solanum tuberosum L.), and alfalfa 24 (Medicago sativa L.), contain multiple copies of the same chromosome set, which can all pair and exchange 25 1 Cappai et al. QTL Map for Blueberry Harvest genetic material during gamete formation. In contrast, allopolyploids, such as wheat (Triticum aestivum 26 L.), coffee (Coffea arabica L.), and strawberry (Fragaria ananassa Duch.) contain two or more divergent 27 genomes, which usually show bivalent pairing and have disomic inheritance, like diploid organisms. 28 While in diploid systems the study of allelic inheritance is relatively simple, polysomic inheritance in 29 autopolyploids increases the number of possible genetic configurations and impacts downstream genetic 30 analyses, including linkage map construction and quantitative trait loci (QTL) mapping (Bever and Felber, 31 1992). 32 QTL mapping is the association study between phenotypic and genetic variants usually performed by 33 tracking recombination events of the possible QTL along chromosomes (Broman and Sen, 2009). In 34 b...