Burdick, A.B.
We have isolated a number of phenotypically unstable types following seed irradiation with thermal neutrons and x-rays. These types are characterized by various kinds and frequencies of leaf sectoring, most of which appears to be associated with genetic instability.
Unstable types have originated in three different ways from irradiated seed:
Type 1. R1 unstables. As single plants grown from irradiated seed which repeatedly sector for texture or color of leaf.
Type 2. R2 single plant unstables. As single plants or as anticlinal segments of single plants in the progeny of plants grown from irradiated seed.
Type 3. R2 segregating unstables. As ca. 25% of the progeny of plants grown from irradiated seed.
Type 1 unstables frequently appear (perhaps 1 out of 100 plants grown from 30,OOO r treated seed) and quite often can be maintained by vegetative reproduction although the unstable condition may be lost eventually due to overgrowth by normal tissue. We have attempted to save only a few of these and they have all been sterile.
Type 2 unstables have appeared in eight different R2 populations (out of about 150 observed) and have always occured as single plants or as single branches. These plants are usually fertile, having normal pollen and normal seed-set. Two of the eight observed have been tested for seed transmission. In both cases the seed vas 100% viable but all the seedlings died in cotyledon stage, presumably because of their having been produced in chlorophyl-deficient sectors on the original unstable plant. Another Type 2 unstable plant, isolated by Mr. Mertens, sectors both anticlinally and periclinally and produces ca. 100% viable gametes in both chlortic and normall tissue but has not yet been tested for transmission. (Type 2 unstables of spontaneous origin are more or less familiar to most tomato grovers although I don't believe any have been analysed genetically nor have I ever observed any in my cultures before.)
Type 3 unstables have as eared as ca. 25% of the progeny in four different ent R2 populations. One of these (m-2) has been shown by Merters (TGC #6) to breed true for the unstable condition and to segregate as a single recessive gene from various heterozygotes. Other Type 3's have not yet been tested. MacArthur produced a similar Type 3 unstable by X-radiation in about 1936 (L. Butler, Jour. Hered. 43:25-35, 1952) which was located in the first linkage group as a single recessive gene, designated m, for mottled. The gene m, although a typical Type 3 unstable, is phenotypically dissimilar from the four we have observed and has not yet been studied in detail. (AEC contract AT (11-1) 335).