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Four secondary trisomics, identified by pachytene analysis in Solanum chacoense Bitt., were analyzed with the Giemsa stain technique. The clones V1700.8 and V1700.24 which, according to pachytene analysis, were secondary trisomics for the long and short arm of chromosome IV, respectively, were identified as secondary trisomics for the long and short arm of chromosome C, respectively, in Giemsa stained somatic cells. Clone V1700.1, a secondary trisomic for the long arm of chromosome IX, was identified as having an extra isochromosome for the long arm of chromosome F, and clone V1700.4, a secondary trisomic for the short arm of chromosome IX, was identified as having an extra isochromosome for the short arm of chromosome F. Chromosomes IV and IX in pachytene correspond to chromosome C and F, respectively in Giesma stained somatic cells. It was possible to locate the centromeres of the chromosomes by using pairs of secondary trisomics. The morphology of the short chromosomes is described in detail to facilitate their identification.

The triploids recovered from 4x × 2x crosses in three Solanum species were very vigorous and although few seeds/fruit were obtained when the triploids were crossed to diploids, the extensive crossing programme produced sufficient seed of four species cph, chc, pnt and tar. The average seed set for the 3x-2x crosses was an extremely low 3.5 seeds/fruit.Approximately 90~ of the progeny of the 3x 2x crosses were aneuploids with chromosome numbers of 2n = 25-29. The frequency of the aneuptoids in the three species that were studied was chc 93%, pnt 94°(, and tar 92~o. The aneuploids of chc and tar were extremely vigorous and fertile and they were used as females in crosses to the marker stocks. The aneuploids ofpnt were vigorous, but the crossability barrier of pnt prevented their use in crosses to the marker stocks. A number of the aneuploids produced seed upon being selfed, but the ability to produce self seed may be related to the pseudo-compatibility of the parental clones. In only 7 aneuploids was there an indication that the self fertility was due to overcoming the selfincompatibility barrier as a result of competition-interaction of the aneuploid gamete.Plants in the families from the triploid-diploid crosses had a tremendous amount of variation in morphological characteristics (leaf shape, size and color; berry shape, color and degree or verrucose spotting; and plant habit and vigor). A large portion of variation exhibited in these families was due to the normal genetic segregation of the heterozygous parents. It was impossible to distinguish the aneuploids from their diploid sibs especially those having only one or two additional chromosomes because they were as vigorous and fertile as the diploids.There were some preliminary indications of the existence of distinct morphological characteristics among the aneuploids (separate petals, long berries, and extreme verrucose berries). However, there was no indication that these traits were due to the dosage effect of the extra chromosome. If it should be determined that this was true, it would be extremely useful in associating genes with chromosomes and determining the phenotypic effects due to the presence of an additional chromosome.Euphytica 24 (1975) ANEUPLOIDS IN SOLANUM markers with chromosomes. The intraspecific aneuploids can be effectively used to this end because of their excellent vigor and fertility.