Self-incompatibility has been discovered in Lopersicon peruvianum and established in six separate collections of the species type, nine of the variety L. p. dentatum and one of L. p. humifusum. L. hirsutum and L. glandulosum are also self-incompatible. L. hirsutum var. glabratum is self-fertile. L. cheesmanii, the only other know species of the section Eriopersicon, was not available for investigation.
In peruvianum progenies from controlled crosses can be divided into two or four intra-sterile, inter-fertile groups. These compatibility reactions and the reactions between the fertility groups and their parents and grandparents agree in all respects with the Nicotiana scheme of oppositional factors.
Fruits and seeds are set rarely after incompatible matings. Pseudofertility seems to occur in plants that are slightly weakened by lack of mineral nutrients.
Compatibility relations of L. esculentum, L. peruvianum, and their F1 and F2 hybrids were studied. The self-incompatibility of the F1 is identical in intensity and apparently in nature with that of L. peruvianum. The observed relations can be explained by assuming that the alleles of L. peruvianum prevent the functioning of identical S alleles and also the allele from L. esculentum. In order to explain the fact that pollen of the F1 and most of the F2 segregates will not function on styles of unrelated plants of L. peruvianum, an independent action---possibly by a dominant gene from L. esculentum--must also be assumed. In contrast to the action of the S genes, thc second effect in the pollen is sporophytically determined.
According to cytological examination of incompatibly pollinated styles and stigmas, pollen germinates normally, but the tubes always swell or burst at their tips. Incompatible tubes rarely reach the base of the style; most grow less than 1/4 the length of the style. The greater inhibition of esculentum pollen on peruvianum styles might be related to the indenendent, sporophytically-determined incompatibility.
An understanding of self-incompatibity sheds light on the phylogeny of the species of Lycopersicon. It also has a significant bearing, on the use of L. peruvianum in the improvement of comercial tomatoes. A method to utilize self-incompatibility in large-scale production of F1 hybrid tomatoes is suggested.