THE LINKAGE MAP OF CHROMOSOME 2 OF THE TOMATO

Abstract

The data accumulated over the past 30 years from the classification of some half a million plants are presented. It is shown that the mapping of chromosome 2, the former linkage group 1, presents many difficulties because of the lethal nature of Wo, and the reduced viability of ro, dv, and m. The problem of classification of o, bk, and ms10also presents difficulties. The examination of the monogenic ratios shows many of them to be disturbed because of lethality, viability, and misclassification, but these causes do not account for all the discrepancies. In the case of Wo and aw there are large excesses of the dominant class; this evidence along with data from anomalous recombination values indicates a chromosomal abnormality. It is suggested that this abnormality is a duplication which in some stocks gives two Wo loci about 25% apart, and two aw less than 40% apart, and also involves the loci of Me and Cu.The recombination values indicate that the map is dv 3 m 2 d 4 p 10 aw (psoro) 13 Me (Cubk) 4 Wo 2 ms105 s. The five genes within the brackets are in the positions indicated but the recombination values within each bracket are not known. While this linear order gives the best synthesis of the 61 recombination values, it also reveals several exceptions. The awps and awo values which should be less than 10% are 40%, and ps o which should be 3% is 26%. Significant differences of more than 10% are also registered between sets of data for the same pair of genes; this is another indication of chromosomal changes. The findings presented here should furnish a framework for more critical examination of specific sections of this linkage group.