Immunological Studies on the Tuber-bearing Solanums: II. Relationships of the North American Species

Investigations using the Ouchtlerlony double-diffusion techniqueand immuno-electrophoretic analysis showed a much greater numberand diversity of antigens amongst the North American speciesof Solomon than had been found previously amongst the SouthAmerican ones. Double diffusion against antisera to S. tuberosum,S. acaule, S. iopetalum, S. bulbocastanum, and S. cardiophyllumsubsp. ehrenbergii, showed a difference between the speciesin series Bulbocastana and Pinnati-secta, and those in seriesLongipedicellata and Demissa. This technique did not providemuch information on the similarities or differences betweenthe species within these two groups. However, immuno-electrophoreticanalysis of the same species with the antisera to S. bulbocastanumand to S. iopetalum gave results which were easier to analyse,and provided much greater resolution of the individual species. At least one identical antigen was found in all the speciesstudied. Some antigens were consistently present in all speciesin certain series, while others had no apparent significancein their occurrence. Three fast-moving antigens were found tohave different, but characteristic, relative mobilities in differentspecies in the series Bulbocastana and Pinnatisecta. The relativemobilities of these three components were similar in the twosubspecies of S. cardiopkyllum and in S. sam-budnum which isconsidered to be a hybrid of subsp. ehrenbergii with S. pinnatisectum. A separate study on S. moreUiforme and S. clarum emphasizedthe distinctness of S. moreUiforme from all other potatoes,but indicated that S. clarum was more closely related to S.bulbocastanum and subsp. ehrenbergii than to S. tuberosum. With antisera to S. tuberosum and S. iopetalum on the one hand,and to S. bulbocastanum on the other, extracts of S. polyadeniumwere found to react more strongly than the species in seriesBulbocastana and Pinnatisecta with the first two antisera, andmore strongly than those in Longipedicellata and Demissa withthe other antiserum. This indicated that S. polyadenium hadsome of the group-specific antigens from both groups, and therefore,that it may be in some intermediate position between these twomajor groups of species. Problems of evolutionary relationship between Mexican speciesand series are discussed in the light of serological, morphological,arid cytogenetical evidence.