The homozygous lanceolate mutant in L. esculentum ranges in phenotype from a small and leafless hypocotyl (reduced) to a bushy plant (narrow) with small leaves and sterile inflorescences. Intermediate forms have a few leaves and their shoot apical meristems abort during development. Stettler and Alldredge (1967) observed that seeds from crowded fruits produced a significantly greater number of leafless forms of the homozygous mutant when compared to seeds from noncrowded fruits. Conversely, seeds from noncrowded fruits produced more leafy types. Furthermore, it was our impression that seeds from well fertilized garden-grown heterozygotes produced proportionately more leafy forms than did greenhouse-grown plants which were given an average amount of care. We thus tested the hypothesis that nutrient stress was a determining factor in gene expressivity of the homozygous lanceolate mutant.
Seeds of lanceolate (LA 335) were obtained from Dr. C.M. Rick, and since that time, over 15 generations of selfing has occurred. Four heterozygous plants were grown in the greenhouse and were given, at the age of three weeks, one application of fertilizer. Two of the heterozygotes received no additional fertilizer while the remaining two received weekly applications of fertilizer and monthly applications of fish emulsion until fruit set. Homozygous mutant progeny of fertilized and nonfertilized plants were classified into leafy and leafless categories (Table 1).
Table 1. Progeny of fertilized and nonfertilized lanceolate.
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lanceolate La/La La/+ +/+ total
leafy leafless
fertilized 11 19 56 31 11
nonfertilized 10 40 89 44 183
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A test of independence using a contingency table revealed a highly significant
difference between the number of leafless forms originating from seeds of
fertilized plants and those from nonfertilized plants. Fruit set was also
diminished in the nutrient deprived plants. Not all fruits on the fertilized
heterozygotes were used for the comparison. The ratio, however, of 11 leafy
to 19 leafless forms generally agrees with what is seen in progeny from
greenhouse-grown plants which receive the standard amounts of fertilizer.The hypothesis that environmental stress influences expressivity of the La gene in the homozygous lanceolate mutant was supported by the earlier study of Stettler and Alldredge (1967) as well as by the present study.
Literature cited:
Stettler, R.F. and A. Alldredge. 1967. Fruit environment affects the phenotypic expression of the lanceolate gene. Rept. Tom. Genet. Coop. 17:51.