Partial Suppression of Hair Development Indirectly Affecting Fruitfulness and the Proportion of Cross-Pollination in a Tomato Mutant

The morphology, inheritance and fertility relations of a tomato mutant are described in this paper. This character behaves as a typical recessive gene in respect to its transmission in selfings of the original mutant, to the characteristics of its hybrids with the normal type, and to second-generation segregations. The fundamental effect of this gene is a partial suppression of hair development. Fruitfulness is secondarily affected-a fact accounting for the discovery of this mutation. Plants of the mutant type were found in fields independently on two separate occasions. Since all hybrids between these two original mutants show the same mutant characters, the genes in each must be allelic and probably identical. In the mutant the hairs of stems, petioles, pedicels and peduncles are modified in form and reduced in number in the manner detailed in the text. Hairs on the corolla segment tips are also reduced, permitting earlier spreading of the tips. The hairs that, in the normal type, bind anthers together to form the staminal tube are absent, permitting the anthers to diverge. This mutant is called the dialytic (dl) type, because the separation of anthers is the only obvious change in gross morphology. Under field conditions the dialytic plants produce only about ten per cent. as many fruits as normal plants; when self-pollinated by hand, they manifest a gamete fertility equal to the normal type. The proportion of hybrids in their progeny indicates that nearly half of the seeds set by the dialytic type under open-pollination result from outcrossing, whereas outcrossing occurs in the normal type to the extent of only one or two per cent. The great reduction in set of fruit and seed indicates that this increase in the proportion of hybrid offspring probably reflects a reduction in the amount of self-pollination to a much greater degree than an increase in the amount of cross-pollination. These changes in fertility relations of the mutant are attributed to the disruption of the normal mechanism for self-pollination wrought by the separation of anthers. Union of anthers is evidently essential to normal self-pollination of the tomato flower under our conditions. Judging from comparisons with fertility relations of male-sterile mutants and from certain aspects of the data pertaining to the rate of outcrossing, the flowers of the dialytic type set fruits only after pollen is transferred to them by insects. The bearing of these findings on the origin of the genus Lycopersicon is briefly discussed.