CYTOGENETIC STUDIES IN TUBEROUS SOLANUM SPECIES

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Abstract
Summary: Meiosis was studied in S. × vallis‐mexici (2n =36). Chromosome pairing tends towards the production of 12 bivalents and 12 univalents per cell. This indicates that the chromosome complement of S. ×vallis‐mexici consists of two similar genomes and one dissimilar genome which in turn suggests that this species is a hybrid between a diploid and an unrelated tetraploid species.Bukasov (1939) and Hawkes (1956) suggest from morphological and geographical evidence that S. × vallis‐mexici is a natural hybrid between S. verrucosum (2n = 24) and S. stoloniferum (2n = 28). Thirty‐four triploid (2n = 36) hybrids, one aneuploid (2n = 37) hybrid and one tetraploid (2n = 48) hybrid were produced by crossing plants from two families of S. verrucosum with four different varieties of S. stoloniferum, C.P.C. 9.1, 9.2, 1331 and 2282.3.The leaflet index and corolla shape were scored in each plant. Meiosis was also studied in detail. Those hybrids resulting from the use of C.P.C. 1331 and to a lesser degree those obtained using C.P.C. 9.1 and 9.2 are morphologically and cytologically similar to S. × vallis‐mexici. Hybrids produced using C.P.C. 2282.3 have leaflet indices similar to it, and corollas shaped like those of S. verrucosum.These differences between the synthesized hybrids can also be expected to occur in natural hybrids. It is suggested, therefore, that the name S. × vallis‐mexici should be applied to all forms of hybrids between S. verrucosum and S. stoloniferum irrespective of whether or not they conform to the type.