POLYEMBRYONY IN TOMATOES

Abstract

Twenty-nine polyembryonic seeds were found among 26,000 tomato seeds. These gave rise to twin seedlings. Five of the polyembryonic seeds appeared as a "double" seed with two units joined at adjacent sides to form the seed. Five pairs of conjoined seedlings were found. In some pairs, one member was four or five times larger than its mate. All the mature twins appeared to be diploid. One true-breeding mature twin may have been a haploid whose chromosome complement was spontaneously doubled. Most of the twin seedlings were from parents which were heterozygous for the gene U (uniform green fruits). The U-genotypes of 32 such twins were determined from F3segregation. The results indicate that most twins resulted from normal segregation and recombination. Therefore, simple polyembryony appears to be the most likely origin of most tomato twin seedlings. False polyembryony due to fusion of two ovules, and euploid polyembryony may account for a few twins. Sporophytic and cleavage polyembryony appear to be relatively unimportant.