Phenotyping of Tomato for SolCAP and Onward into the Void

Abstract

Standardized phenotyping is being used in tomato (Solanum lycopersicum) and potato (S. tuberosum) as part of the USDA-funded Solanaceae coordinated agricultural project (SolCAP). In tomato, a panel of 480 lines, 144 fresh market, 144 processing, 44 vintage lines, 48 landraces, and 101 related Solanum species accessions, are being grown over two seasons at multiple locations. These tomato genotypes will also be screened for over 7600 single nucleotide polymorphism markers that are being developed. Characters being phenotyped are hypocotyl color, plant habit, inflorescence (simple or compound), flower fasciation, flowering time, time to maturity, size of blossom scar, and pedicel type (jointless or jointed). Transverse and equatorial cross-sections of fruit are also being scanned to obtain measures of fruit shape and color by tomato analyzer computer software. Other fruit characters being measured are pH, titratable acidity, and soluble solids. Some useful information may come from this phenotyping and genotyping effort. However, in this author's opinion, the value of measuring some of the traits is very limited in the face of much more important breeding traits that are difficult to fit into a standardized phenotyping format. For instance, proper assessment of several fruit disorders is not being attempted, but such data might yield some invaluable marker information. Part of this is the result of funding limitations for the phenotyping effort. However, a major benefit of the SolCAP analysis will be the development of markers that will differentiate the lines being studied, because there is a present lack of polymorphisms in tomato germplasm where wild species introgressions are minimal or distant in time. This will allow breeders to proactively select for recurrent parent backgrounds in backcrossing projects and may aid in the identification of associations of markers with important characteristics. As one looks to the future of standardized phenotyping, there are some important traits that will be difficult to phenotype such as tomato flavor, which is quite subjective and for which there are no good objective measures.