Rick, C. M.
Studies of this interesting acession were continued in 1960. A series of direct and reciprocal test crosses was completed between S. pennellii and all available species of Lycopersicon as well as the closely related solani, S. lycopersicoides and S. ochranthum. Results were consistent in the some that the same pattern of reaction was observed in most flowers of a given cross combination. Most exceptions dealt with combinations which generally failed, but in which one or a few exceptional fruits produced viable seeds. In every instance in which such lots were sown the resulting seedlings proved to be entirely of maternal type, revealing self-contamination. Such instances were mostly limited to crosses with S. pennellii as female parent, thanks to its self-compatibility and exceedingly prolific pollen production. The only crosses that succeeded in producing hybrid offspring were between S. pennellii and members of the intercompatible esculentum-hirstum complex, including the two taxonomic variants of L. hirsutum, L. esculentum (many genotypes), L. esculentum var. minor (Galapagos accessions), and L. pimpinellifollium. The incompatible matings (all of which were with SI species) generally failed to set fruit in the other combinations in which S. pennellii was used as female parent, while in the reciprocals generally small seedlees fruits vere set. The F1 hybrids of the intercompatible combinations generally conformed to the fertility pattern previously described for the L. esculentum-S. pennellii hybrids, and showed morphological intermediacy between the parents.
Test populations of derivative generations of F1 L. esculentum-S. pennellii were grown in the greenhouse and field. This material proved as amenable for genetic purposes as the F1. The F1 and BC seeds germinate well, particularly if treated with sodium hypochlorite as outlined in another Research Note. Only a small proportion of the seedlings are weak, the rest grow vigorously in either field or greenhouse. Most individuals in these generations do not set fruit well. without aid. An inherited tendency toward unfruitfulness must be one of the causes of the poor fruiting observed in the field as well as hybrid sterility because the pennelli parent itself is completely barren in the field. Pollen fertility is expectedly variable, in F2 a range from 10 to 100% abortion was observed. Test crosses of L. esculentum x F2 reveald, however, that the steriliy was seldom so complete that at least a few progeny might not be produced. Performance of the hybrid tetraploids is even more gratifying, for they continue to reproduce with greater fertility than comparable diploids. Such evidence for their segmental alloploid nature has been borne out by cytological analysis of chromosome pairing and by preliminary segregations for esculentum marker genes, the yield of mltiple recessives being far less than expected on the basis of random pairing.
Genetic analysis of these hybrids is proceeding but only the following brief resume is justified. Segregation of esculentum markers has not deviated from normal in BC\esc. For the F2 a tendency toward a deficiency of the marker homozygotes has been observed. It seems to be of a similar nature to that of the L. esculentum-chilense F2, though possibly less intense. Inheritance of all species-distinguishing characters analyzed thus far follows the expected quantitative pattern. A variable reduction in stamens is observed in BC\pen, cytoplasmic influence being suspected. Our present research program is proceeding along these lines as well as systematic backcrossing of marked pennellii chromosenes into esculentum genetic backgrounds to test the effect on recombination rates and other phenomena.
These additional results uniformly bear out the doubts expressed earlier about the taxonomic position of S. pennellii. It is unquestionably more closely allied to the tomatoes than to the nightshades.