Inheritance of High Sugars from Tomato Accession PI 270248 and Environmental Variation between Seasons

Small-fruited cherry tomato accession PI 270248 (Lycopersicon esculentum Mill. var. cerasiforme (Dunal) A. Gray) with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) (L. esculentum) that had normal (low) fruit sugars. The F1 was crossed to PI 270248 and 7833 to obtain BCP1 and BCP2, respectively, and self- pollinated to obtain F2 seed. The resulting population was used to study the inheritance of high sugars from PI 270248. Continuous sugar level frequency distributions of BCP1, BCP2, and F2 suggest that the trait is under polygenic control. Additive variation was signifi cant, but dominance variation was not. There was a heterozygote × heterozygote type of epistasis present that likely caused the F1 sugar level to skew nearly to the level of the high sugar parent. The F2 mean sugar level was lower than the midparent level. Broad-sense heritability was 0.86. There was a signifi cant line × season (fall, spring) interaction where lines with higher sugars were affected more by seasons than lines with lower sugars. Sugar level, in general, was higher in spring. Higher solar radiation in spring than in fall may explain the sugar level difference between the seasons. There is general agreement that fl avor of commercial fresh- market tomatoes could be improved if their fruit sugar concentra- tion was increased (Jones and Scott, 1984; Malundo et al., 1995; Stevens, 1972). There are several small-fruited accessions with high fruit sugars and these can be used as donor parents. These include accessions of L. chmielewskii Rick et al. (Chetelat et al., 1995), L. hirsutum Humb. & Bonpl. (Hadas et al., 1995; Schaf- fer et al., 1998; Stommel and Haynes, 1993), and various cherry tomatoes (Saliba-Colombani et al., 2001). The small-fruited cherry accession PI 270248 ʻSugarʼ was originally of interest in our breeding program because it had a high level of resistance to bacterial spot (Xanthomonas campestris Dye pv. vesicatoria (Doidge) Dye) on its fruit but not foliage (Scott et al., 1989). More recently, we have been interested in using PI 270248 as a source of high sugars for transfer to large-fruited tomato inbreds. Georgelis et al. (2004) identifi ed six randomly amplifi ed polymor- phic DNA (RAPD) markers from PI 270248 that were linked to high sugars in at least three linkage groups. Unfortunately, fi ve of these markers were also linked to small fruit size and the sixth was linked to indeterminate plant habit. These results confi rmed earlier work showing sugars (or soluble solids) to be higher in small fruit (Goldman et al., 1995; McGillivary and Clemente, 1956; Saliba-Colombani et al., 2001) and in indeterminate plants over determinate plants (Emery and Munger, 1970). Thus, the transfer of high sugars from small-fruited accessions to large-fruited, determinate recurrent parents will be diffi cult because of the as- sociations mentioned and the quantitative control of high sugars. The RAPD markers identifi ed (Georgelis et al., 2004) might be helpful, but only if they can be used to select for sugars without either small fruit or indeterminate plant habit. Thus, further work