The jointless pedicel trait of tomato conferred by the j-2 gene is widely used in processing markets for stem-free removal of fruit to accommodate mechanized harvest. Although current utilization of j-2 for fresh-market tomato breeding is limited, interest in this trait may increase as breeders seek to address high labor costs through the development of mechanically harvestable cultivars for the fresh market. Yet, the introduction of this trait into new market classes heavily relies on phenotypic selection because there are presently no high-throughput methods available to genotype j-2. Reliable, high-throughput molecular markers to genotype the presence/absence of j-2 for selective breeding were developed. The molecular markers described here use the high-resolution DNA melting analysis (HRM) genotyping with single-nucleotide polymorphism (SNP) and derived cleaved amplified polymorphic sequence (dCAPS)–based genotyping. Two separate HRM-based markers target the j-2 on chromosome 12 or a linked sequence region 3.5 Mbp apart from the gene, and a dCAPS marker resides on the latter. We demonstrate the association between each marker and the jointless pedicel phenotype using segregating populations of diverse filial generations in multiple genetic backgrounds. These markers provide a useful resource for marker-assisted selection of j-2 in breeding populations.
Tong Geon Lee, Reza Shekasteband, Naama Menda, Lukas A. Mueller, and Samuel F. Hutton
Heather L. Merk, Shawn C. Yarnes, Allen Van Deynze, Nankui Tong, Naama Menda, Lukas A. Mueller, Martha A. Mutschler, Steven A. Loewen, James R. Myers, and David M. Francis
For many horticultural crops, selection is based on quality as well as yield. To investigate the distribution of trait variation and identify those attributes appropriate for developing selection indices, we collected and organized information related to fruit size, shape, color, soluble solids, acid, and yield traits for 143 processing tomato (Solanum lycopersicum L.) lines from North America. Evaluation of the germplasm panel was conducted in a multiyear, multilocation trial. Data were stored in a flat-file format and in a trait ontology database, providing a public archive. We estimated variance components and proportion of variance resulting from genetics for each trait. Genetic variance was low to moderate (range, 0.03–0.51) for most traits, indicating high environmental influence on trait expression and/or complex genetic architecture. Phenotypic values for each line were estimated across environments as best linear unbiased predictors (BLUPs). Principal components (PC) analysis using the trait BLUPs provided a means to assess which traits explained variation in the germplasm. The first two PCs explained 28.0% and 16.2% of the variance and were heavily weighted by measures of fruit shape and size. The third PC explained 12.9% of the phenotypic variance and was determined by fruit color and yield components. Trait BLUPs and the first three PCs were also used to explore the relationship between phenotypes and the origin of the accessions. We were able to differentiate germplasm for fruit size, fruit shape, yield, soluble solids, and color based on origin, indicating regional breeding programs provide a source of trait variation. These analyses suggest that multitrait selection indices could be established that encompass quality traits in addition to yield. However, such indices will need to balance trait correlations and be consistent with market valuation.