Aurea and yellow green-6 are recessive tomato mutants with a very similar phenotype. Recently we isolated a new EMS induced recessive mutant (W616) with the same phenotype. All these are characterized by a yellow-green leaf color, an elongated hypocotyl and reduced anthocyanin content. The strongly reduced phytochrome content in these mutants (Koornneef et al., 1985) most probably causes this syndrome. Although we could not find any reports on tests of allelism between au and yg-6, genetic data for au (Khush and Rick, 1968) and yg-6 (Whalen, 1964) firmly established the location of au on chromosome I (very close to sit) and yg-6 on chromosome 11 (near hl; r = 13%), which indicates that they are at different loci. Our W616, three aurea lines (LA536, LA538 and 2-655) and yg-6 (LA1486) obtained from Prof. Rick, were crossed in diallel combinations. All hybrids had the mutant phenotype indicating that W616, au and yg-6 are all allelic. That W616 is allelic to aurea was supported by the absence of double recessive recombinants in an F2 population of 1387 plants derived from a cross between W616 and our wilty mutant W697, which is allelic to sit. Seed admixture seemed an unlikely explanation for the unexpected results of the allelism-test, for the yg-6 background (a Cherry type) agrees well with that described in TGC Report No. 12 (p. 14). From the dominant fruit characters of yg-6 it could also be excluded that the F1 W616 x yg-6 and the F1 x yg-6 were self-pollinations of @616 and au respectively. Because yg-6 is a radiation-induced mutant we suspected that a translocation might explain the contradiction between the results of the allelism-tests and the linkage data.
In view of this, pollen viability and meiosis were checked in the F1 W616 x yg-6. A number (not all) of these plants were semi-sterile and had quadravalents in meiosis. In the pachytene stage, chromosomes I and 11 could be unambiguously identified as the chromosomes involved in the reciprocal translocation; thus, it appears that the yg-6 stock (LA1486) was heterozygous for a translocation between chromosomes 1 and 11. This translocation fully explains the linkage of yg-6 with hl and a (chrom. 11) as found by Whalen (1964) and its non-complementation with au (chrom. 1). Therefore, yg-6 is not a distinct locus and should be omitted from the linkage map of chromosome 11.
Literature cited:
Khush, G.S. and C.M. Rick. 1968. Chromosoma 23:452-484.
Koornneef,M.,J.W. Cone, R.G. Dekens, E.G. O'Herne-Roberts, C.J.P. Spruit and R.E. Kendrick. 1985. J. Plant Physiol. 120:153-165.
Whalen, R.H.1964. Tomato Genet. Coop. Rpt. 14:30-31.