The effect of the high pigment genes hp1, and hp2 on certain plant constituents.
The two genes hp1 and hp2 have been incorporated in several lines being bred for high ascorbic acid content. After the 1956 assays had been made it was noted that some of the plants with the highest ascorbic acid content also had the high pigmentation. About half of the plants had been destroyed because of inferior horticultural characteristics. Hence it was too late to get the complete record on any of the lines. The data on the survivors of the F2 populations segregating for high pigment are given in Table I. The ascorbic acid content of the hp1hp2 plants is about 2@4%, higher than that of the normal segregants. This probably is a pleiotropic effect rather than linked genes since high pigment and high ascorbic acid are in repulsion. Eight segregating P3 lines and six green-house lines also support this conclusion. The association between ascorbic acid content and an easily identified plant characteristic may expedite breeding for this vitamin.
The high piment plants were a little later in maturity and less productive than the normals. As reported by Thompson, high pigmentation is associated with firm fruit. Firmness is also characteristic of most lines with high ascorbic acid content. Previous observations have indicated that the segregants having high pigmentation or the highest ascorbic acid also have smaller fruit size than average. The 1956 data in Table I however do not confirm this. Possibly the selection for superior horticultural characteristics eliminated the plants with the smaller fruit.
When lutescent lines are segregating for high pigmentation the hp plants can be distinguished from + plants by their greater anthocyanin content. The high pigment plants also have more chlorophyll than normal as hp a plants are darker than + a plants. Hence the high pigment genes exert their influence on the following biochemical systems: ascorbic acid, anthocyanin, lycopene, beta-carotene and chlorophill.
Table I Association of the high pirgment genes hp1 hp2 with high ascorbic acid content in F2 populations. High pigment Normal pigment ____________ ______________ increase No.of *Average **Av. No.of *Average **Av. with high Line plants ascorbic size plants ascorbic size pigment ________________________________________________________________ H 2C 1 49.8 2.21 13 40.3 1.82 23.6 H 4B 4 44.4 2.34 15 35.9 2.25 23.6 H 4C 2 53.5 2.25 19 43.6 2.28 22.7 H 4D 4 53.6 2.24 23 42.2 2.17 27.7 H 4H 4 42.2 2.35 21 34.6 2.37 22.0 H 4I 2 52.3 2.10 24 44.4 2.18 17.8 H 9A 5 50.8 1.77 13 43.5 1.74 16.8 H 9B 2 59.9 2.05 32 39.7 2.00 50.9 H10A 2 47.8 2.28 24 39.5 2.29 21.0 H10C 3 46.5 2.20 26 43.3 2.06 7.4 H12A 2 48.1 2.25 17 35.1 2.18 37.0 H12B 5 40.2 2.28 39 34.4 2.32 16.9 * Mg. % ascorbic acid by a modification of the indophenol titration method. ** Size index = (polar + equatorial diameter in inches)/2 _______________________________________________________________________