Immunological Studies on the Tuber-bearing Solanums III. Variability within S. bulbocastanum and its hybrids with species in series Pinnatisecta

It was shown in the previous paper of this series that the Mexicanspecies Solanum bulbocastanum, S. cardiophyllum subsp. cardiophyllumand subsp. ehrenbergii, S. michoacanum and S. pinnatisectummay be differentiated to some extent by the double diffusiontechnique, and more fully by immuno-electrophoretic analysis.Above all, the relative electrophoretic mobilities of certaincomponents, as expressed by the index have been found to be very constant for each species, with the apparent exception of S. bulbocastanum. A detailed investigation of S. bulbocastanum has now shown thatalthough the many clones of this species appeared similar whenexamined by double diffusion, differences were exposed by immuno-electrophoreticanalysis. In particular, the values fell into two discrete groups, 0.15 to 0.23 and 0.30 to 0.46. Theplants in these groups had been collected from Oaxaca and Guatemala,and from Central Mexico, respectively. Most of the former grouphad been identified as S. bulbocastanum subsp. partitum, andall the latter group as subsp. bulbocastanum and subsp. dolichophyllum.Not only was the wide variation in values of index resolved into two meaningful groups, but it was also found thatall lines within any one collection had almost identical values. The index value for S. cardiophyllum subsp.cardiophyllum is 1.0, and for subsp. ehrenbergii is 0.7. The F₁ hybrids between either ofthese subspecies and S. bulbocastanum had fairly uniform valuesclose to the calculated means of the parental values. The shapesof the leaves of these hybrids were also uniform and more orless intermediate between those of the parents in each case. The F₂ hybrids between S. bulbocastanum and S. pinnatisectum,and also the triple hybrids between these two species and eitherS. cardiophyllum or S. michoacanum, showed a wide range of valuesof index and of leaf shapes, with partial segregation towards the parental types. The serological andmorphological characters segregated independently. S. X sambucinum was found to have a wide variation in serologicaland morphological characters. This variation was consistentwith the theory that S. X sambucinum is a natural hybrid betweenS. pinnatisectum and S. cardiophyllum subsp. ehrenbergii. Within the groups of species investigated, the relative electrophoreticmobilities of certain antigens as displayed by immuno-electrophoreticanalysis were found to vary significantly in different species,in different subspecies of the same species, and in specieshybrids.