Juvenile albino, a Virescent Mutant in Watermelon: Inheritance and Expression

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juvenile albino (ja) is a spontaneous mutant, first observed in 1992. Hypocotyls, new young leaves, shoot tips, tendrils, and flowers on the main shoot of the ja mutant are all albino during early spring and late fall. The interior of the albino leaves gradually become green, while the margins remain albino. Fruit rind color of the mutant is variegated. Growth of the ja mutant is severely impaired in the early spring and late fall. However, the mutant grows almost normal in the summer, and produces fruits of almost normal size. Genetic analysis of F1, F2, and BC1 populations derived from the ja mutant showed that ja mutant is inherited as a single, recessive, nuclear gene. The segregation ratios in the F2 and BC1 progenies derived from the cross between the previously reported dg virescent mutant and the ja mutant indicated that both are inherited independently. Experiments with temperature (3–5C vs. 20–22C at night), day length (8 vs. 15 h), and red and/or far-red light (15 vs. 0 min) at the end of an 8-h day were performed to investigate the regulation of ja trait expression. Temperature and red/far-red light had no differential effect on mutant and wild-type plants. However, significantly increased fresh weight and chlorophyll content were observed in the ja mutant over the wild-type when grown under long-day conditions. In addition, chlorophyll synthesis or accumulation in the mutant is severely impaired under short-day conditions. To our knowledge, this is the only virescent mutant in Cucurbitaceae whose expression is regulated by day length.