Reduced Plant Growth in Tomato Mutants high pigment and dark green Partially Overcome by Gibberellin

Abstract

Table 1. Stem length and plant dry weight of high pigment (hp) and dark green (dg) and normal tomato plants, with and without the application of exogenous gibberellic acid (GA7). Genetic mutants high pigment (hp) and dark green (dg) were first recognized and described in tomato (Lycopersicon esculentum Mill.) because of their effects on chlorophyll content in vegetative parts and carotenoid pigments in the fruit (Kerr, 1960; Konsler, 1973). Both mutants affect several other unrelated characteristics, including enhanced ascorbic acid (vitamin C), increased fruit firmness, brittle stems, and reduced plant growth (Jarret et al., 1984). The two mutants are not allelic (Jarret et al., 1984; Thompson, 1961; Wann et al., 1985), yet their effects on the whole plant are almost identical. The hp and dg genotypes cannot be distinguished from each other based on phenotype alone. The multiple effects of hp and dg have been described as pleiotropy rather than genetic linkages (Jarret et al., 1984). The effects of hp and dg on fruit quality are considered beneficial. Their practical use, however, has been restricted due to reduced plant growth. Numerous attempts have been made to overcome the growth-retarding effects of hp and dg through conventional breeding and selection procedures. To date, none of the segregating populations have produced recombinant individuals with normal growth. Jarret et al. (1984) reported that hp and dg decreased stem length, leaf area, and wholeplant fresh and dry weights, but did not affect the number of nodes. The phenotypes relative to plant morphology resemble those described for gibberellin-deficient mutants in tomato (Koornneef et al., 1990). I endeavored to determine whether exogenous gibberellin would overcome the growth-retarding effect of mutants hp and dg. Tomato breeding lines carrying the hp and dg genes were crossed with ‘Flora-Dade’. The mutant genotypes were reselected from segre-