A new selection method for seedling identification of hp using photoselective vinyl film was studied. Just after germination, seedlings of 17 tomato lines including F1 hybrids, which possessed the hp, Ip, and og genes, were covered for 10 days with 4 kinds of vinyl films. Light transmission properties of the films are given in Figure 1.
Results are summarized in Figure 2. Under red and yellow films, all of the lines except the hp homozygous lines showed remarkably spindly growth and it seemed that the purple color of the hypocotyl, a result of the presence of anthocyanins, had disappeared. On the other hand, the hp lines showed moderate hypocotyl growth and their anthocyanin had not disappeared. These results indicate that blue light (400-500nm) is necessary for young tomato plants (except for hp lines) to prevent spindly growth and to develop anthocyanin. It is possible to distinguish the hp seedlings from normal at the cotyledon stage by this method. For practical purposes, yellow film is better for selection because of the growth of a stronger plant than under red film.
To clarify the mechanism of the disappearance of the purple color, young tomato seedlings treated with yellow film were collected and anthocyanin was extracted with 1%-HC1-95%-methanol for spectrophotometry and TLC (silicagel G 250 micron, butanol 4; acetic acid 1; water 5). Results are simmarized in Figure 3. The absorption maximum of anthocyanins from all samples was the same (approx. 545nm) but the hp lines showed a stronger absorption peak than normal lines. All the samples showed the same Rf (0.84) in TLC. These results indicate that there is no difference in the kinds of anthocyanin between hp and normal lines, but that hp lines simply possess larger amounts of anthocyanin under the conditions of growth. Although the total amount of anthocyanin was not reduced under yellow film in either line, it seems that the normal lines lose their anthocyanin from their hypocotyl because of a dilution of anthocyanin caused by their spindly growth. Effectiveness of selection of hp plants from segregating populations by the yellow film method was verified by observation of leaf and fruit color in the field. The "Yellow film method" is highly effective for selecting hp plants during early growth.
Fig. 1 Spectral transmittance of vinyl films used in this experiment.
Fig. 2 Effect of covering with 4 kinds of films on hypocotyl length and intensity of purple color in cotyledon stage.
Fig. 3 Varietal difference of hypocotyl length and anthocyanin amount under yellow film.