Variegation Initiated by a Dominant Allele in the Tomato.

HE locus of Woolly is in chromosome 2 of the tomato, Lycopersicon escuZentum, in which the basic chromosome number is 12. Three alleles, in addition to the normal non-Woolly allele, WO+, are known. WO and Wov are dominant and lethal when homozygous, and WO"' is partially dominant and viable when homozygous (RICK and BUTLER 1956). Woolly plants have thicker, longer trichomes than the normal and in WO and WO'' many of them are branched. Sectors of abnormal tissue were observed on the leaves and stem of young seedlings containing the dominant allele WO, the original Woolly discovered by W. S. PORTE (YOUNG and MACARTHUR 1947). The variegation consists of sectors and irregular patches varying in shape, and occurs not only on Wo/Wo+ plants but on non-Woolly Wo+/Wo+ plants originating from Woolly. On a variegated plant one o r more leaflets of the first four true leaves may have a pale green sector. Abnormally dark green sectors also occur. The color changes are far more conspicuous on the upper surface of the leaf. Another type of change consists in partial or total loss of epidermal hairs in certain areas. A dark green color is simply due to loss of hairs, but a darker green color is often observed. Distortion of the lamina often accompanies changes in green color (Figure 1A). Pale sectors are the commonest and are sometimes less pubescent but never glabrous. More conspicuous but less frequent are the dark sectors, usually distorted and glabrous. Pale, dark, and less hairy sectors may occur on the same plant. Some Woolly plants had both less pubescent and glabrous sectors. Occasionally, pale and dark sectors occur in juxtaposition, suggesting the twin spots found in Drosophila and in maize kernels (STERN 1936; JONES 1936). Usually a sector constituted a well defined part of the lamina of a leaf. The extent of the sector varied from one-haif leaflet to a very small patch. Some leaflets had a rough mottled appearance, owing to small patches of normal and mutant tissue. Longitudinal stripes of mutant tissue often occur on the stem (Figure 1C). Sectors are much more common in the juvenile stage, particularly in the first