A study has been made of the inheritance of a number of various characters in watermelons. Data were obtained from parent selections and from F1, F2 and backcross progenies in 1934.
The difference between elongate and spherical fruits was found to be determined by a single pair of genes which lacked dominance. Heterozygous individuals bore fruits which were intermediate in shape.
Shapes of young ovaries were inherited in the same manner as shapes of fruits, but the segregation was more clear-cut in the case of ovaries. Shapes of mature fruits and shapes of young ovaries were very highly correlated.
Small size of fruits may be considered dominant if the data for fruit weight are plotted arithmetically, but if the data are plotted logarithmically the genes for size must be regarded as lacking dominance and having proportional effects.
Many correlation coefficients are presented in an effort to show the relationships between time of flowering, time of maturity, and length, width, shape and weight of fruits in the watermelon.
There was highly significant negative correlation of fruit shape with fruit weight (r= -.34 and -.41 in F2).
The data indicate that one major gene largely determines small size of seed in contrast to large size of seed in the cross of Long Iowa Belle X Japan 4. Those F1 plants having the large-seeded Iowa Belle as female parent blossomed earlier, matured fruits earlier and produced larger fruits than the reciprocal F1 plants with the small-seeded Japan 4 as female parent.
Dark-green rind was dominant to light-green rind and was determined by one gene, though other genes apparently deter· mined minor variations of the light color. The type of broad striping found in the China 23 watermelon seemed to be due to a single recessive factor when crossed with the dark-green Iowa Belle but was dominant when crossed with the light-colored Japan 6. Apparently the striping gene either forms a multiple-allelomorphic series with the genes for dark and light-green rind color, or it is very closely linked with these genes. The genes for striping and those for dark and light green are all linked in about the same degree with the gene for Iowa Belle mottling or its allelomorph.
The Iowa Belle mottling (IB) was determined by a single gene in two crosses and was recessive. However, in the cross of Iowa Belle X Japan 6, the heterozygous fruits carried an intermediate type of marking (sub-IB). Secondary factors apparently affected the dominance of the non-IB gene.
The Iowa Belle rind marking was highly correlated with length, width and weight of fruits in the cross of Iowa Belle X Japan 6. This indicates that a size gene may be linked with the color factor. The fact that size and shape are also correlated, while the Iowa Belle marking is not linked with shape, indicates that there are two genes for size and that they are carried on different chromosomes.
The data indicate that the presence of a peripheral black band on the seed coat is a dominant character, that reddish brown is dominant to light tan, and that the combination of the genes for reddish brown and black bands gives black over the entire seed coat.
Weetman, Leslie M.
"Inheritance and correlation of shape, size and color in the watermelon, Citrullus Vulgaris Schrad.,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 20
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol20/iss228/1