Beta-carotene is the principle provitamin A carotenoid present in tomato fruit. This carotenoid, however, only accounts for up to 5-10% of the total carotenoids found in typical ripe red-fruited tomatoes. Lycopene, which has no provitamin A activity, constitutes 50-70% of the total carotenes. High beta-carotene tomatoes derived from introgression of the dominant B allele from L. hirsutum into L. esculentum have been described (Lincoln and Porter 1950, Tomes et al. 1956). Incorporation of B results in beta-carotene accumulation at the expense of lycopene and a shift in fruit color from red to orange. Rick (1956) notes the presence of B or a very similar allele in L cheesmanii. Contrasting with numerous reports describing the action of B from L. hirsutum in L esculentum, little is noted concerning the B-like allele from L. cheesmanii.
In contrast with the green fruited L. hirsutum, fruit of L. cheesmanii are orange pigmented and F1 plants obtained from crosses with L. esculentum bear smooth, deep orange colored fruit. Seed is readily obtained from the initial cross of L. cheesmanii with L. esculentum and from F1 backcross generations. Analysis of carotenoid content in fruit of F1 plants confirmed that the orange pigmentation is attributable to beta-carotene and that this provitamin A carotenoid accounted for nearly 70% of the total carotenoids present (Table 1).
The behavior of L. cheesmanii in interspecific crosses highlight several drawbacks of using L. hirsutum accessions as sources of the B allele. Low seed yields result upon making the initial cross with L esculentum and are prevalent in subsequent backcross generations. Additionally, F1's bear rough and very crack susceptible yellow/orange fruit. Although likely, unequivocal evidence that the B-like allele present in L. cheesmanii is identical to the B allele found in L. hirsutum, has not been established. In light of the advantages L. cheesmanii offers as a donor parent in crosses with L. esculentum, additional efforts are underway to better characterize this allele and its interaction with other genes controlling carotene biosynthesis.
Lincoln, R.E. and J.W. Porter. 1950. Genetics 35:206-211.
Rick, C.M. 1956. Am. J. Bot. 43:687-696.
Tomes, M.L., F.W. Quackenbush and T.E. Kargel. 1956. Bot. Gaz. 117:248-253.
Table 1. Provitamin A carotenoid content of L. cheesmanii (LA 317), L. esculentum (Floradade, FM6203, Caro-Rich) and F1 hybrids.
______________________________________________________________ Line Beta-carotene* Retinol Beta-carotene (g/g/fresh Wt. S.E.) Equivalent S.E. (% of total carotenoids) ______________________________________________________________ LA317 58.23 4.97 9.04 0.83 86.6 Floradade 1.89 0.39 0.32 0.07 7.4 FM6203 1.42 0.36 0.24 0.06 4.2 Floradade x LA 317 30.93 1.46 5.15 0.24 69.9 FM6203 x LA 317 32.52 5.97 5.42 1.00 64.4 Caro-Rich 27.40 2.51 4.57 0.42 57.5 ______________________________________________________________* Results obtained using HPLC.