By doubling the chromosomes of a haploid tomato asexually (decapitation-callus technique) an absolutely homozygous diploid is produced. Ten generations of severe selection to break this pure line have resulted only in very minor changes, easily attributable to a normal mutation rate. Data on the effect of the selection pressure on dry weight of plants and on size and weight of fruits show no statistically significant effects in two selection lines and a barely significant ( 5 per cent point) effect in a third selection line. Only one major point-mutation was noted among the 12,000 experimental plants (a mutation to a recessive wiry form, different genetically from the original wiry mutant) and this occurred in the control lines. These results are directly opposed to the Russian worker, Lysenko\u27s claims that the tomato deteriorates in three to five generations. The original haploid, now carried on asexually for 12 years, has proved also to be remarkably stable, only one large bud-sport having been observed
