Abg--
a gene on chromosome 10 for purple fruit derived from S. lycopersicoides
Rick, C.M., Clsneros, P., Chetelat, R.T., and DeVerna, J.W.
Department of Vegetable Crops, University of California, Davis, California 95616.
Fruits of S. lycopersicoides in its native habitat develop strong anthocyanin, often becoming totally jet-
black, in the outer cell layers of the fruit in late stages through maturity. This intensity is seldom reached in fruits of
plants grown outside the native habitat, generally in greenhouses. Light intensity is implicated as a cause of the
difference because areas beneath the calyx or artificially shaded portions of the fruit lack such pigmentation.
Furthermore, the high intensity of solar radiation in the native area (2,000-3,600 m elevation in the Andes of S.
Peru and N. Chile), which has to be experienced to be appreciated, is probably never matched in experimental
plantings elsewhere.
This trait is weakly expressed in the F1 intergeneric hybrids and moderately so in the alien addition line for
chromosome 10, thereby ascertaining its dominance and chromosome location. Segregation was first observed in
BC2 and BC3 progenies from a single derivative of a diploid hybrid. Pigmented BC3 individuals were selfed and
subsequent generations were grown and classified for presence and intensity of pigmentation. Progenies were
grown in the winter greenhouse and summer field, the strongest expression being observed in the latter,
particularly toward the end of the season. Expression in the derivatives did not match that of the nightshade fruits in
the wild but approximated that of the more extreme expression of the latter grown under our greenhouse
conditions. Variegations, as in a spotty or blotchy pattern or sharply defined radial sectors of different intensity, are
other characteristic, yet erratic, features of this phenotype. Exposed areas of developing fruits in the last half of
their development can be totally flushed with anthocyanin, resembling medium-pigmented eggplant fruits, hence
the name Aubergine and symbol Abg. Anthocyanin accumulation is also enhanced by superficial wounding
(punctures, scrapes) of the fruit epidermis. This type of enhancement might account for certain types of the
aforementioned variegation.
Five pooled BC3 families yielded 35 pigmented: 22 normal, the proportion of normals being below
monogenic expectation in each family. The early progenies from selfing proved difficult to score, probably because
classification was attempted under unfavorable conditions. Five BC3S3,4 families segregated 18 Abg: 31 +/Abg: 16
+, the separation between the two pigmented classes proving difficult. Progeny tests were made from one such
family with the following results:
It is thereby evident that we did not succeed in distinguishing Abg/Abg from +/Abg fruit phenotypes;
consequently, only 2-category classifications are reliable. The total F2 segregation thereby becomes 49 Abg ; 16 + -
- a reasonable monogenic segregation.
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