Species Differentiation in Solanum, Sect. Tuberarium : IX. Genomic Relationships between Three Mexican Diploid Species

Abstract

Genomic relationships between three Mexican diploid Solaleums (2n=24). S. bulbocas-tanum (blb), S, jamesii (jam) and S.sambucilcupef (smb), were studied on the basis of meiotic chrcunosome pairing and pollen fertility in the hybrids and amphidiploids induced from them. The F1 hybrids, smbXjam, had as regular meiosis and as high pollen fertility as those fcund in their parents, thus suggesting that the parental genomes are closely related to each other. A similar situettion was also found in the F1 hybrids from sleebXblb, though thcre were a slight reduction in the amount of chromosome pairing and a rare occurrence of chromatid bridges. The F1 hybrids, jamXblb, differed from the above two instances, not only by showing multiple associations in 23-51 of the metaphase I cells examined and more frequent occurrences of chromatid bridges and laggards but also by having a reduced pollen fertility (37-52%) On the other hand, while the smbXjam amphidiploids formed as many multivalents as in their parental autotetraploids, the smbXblb amphidiploids showed, like the jam X blb ones, a significant rcduction in multivalent frequency as compared with their parental autotetraploids. This may be interpreted as due to a higher differential affinity existing between some chromosomes of the parental genomes in the latter two instances. From these results, it is concluded that the .genomes of smb and jam are highly homologous and that the blb genome is distantly related to, though not distinct from, those of the above two species.