Rick, C. M.
Since a preliminary report on this work has been published (PNAS 46:58-63) this note will deal only with some of the little data that have been obtained recently. As previously indicated, the F2 generation from the cross L. esculentum x S. pennellii is relatively viable. About 10% of the plants exhibit various degrees of a non-infectious leaf necrosis similar to that found in esculentum-chilense derivatives. In its extreme form the plants are very stunted and may die before flowering; in milder manifestations the plants flower and fruit despite a slow progressive defoliation that results from the necrosis. The non-afflicted plants grow vigorously without special aids and can flower and set fruits well in 4-inch pots. The mean pollen abortion of 73 plants examined was 33% with a wide range of variation from complete abortion to nearly 100% stainable grains. Nearly all of the plants set fruit with varying seed numbers after crosses with S. pennellii as pollen parent. None set fruit when L. esculentum was used as pollen parent. Preliminary counts reveal a deficiency of homozygotes for marker genes, which were contributed by the esculentum parent.
A small test progeny of 60 plants has been grown from the backcross of the F1 to L. esculentum. These mostly grew with considerable vigor, only one showing the necrotic symptoms. Mean pollen abortion was 29% with a range of variation almost equal to that of the F2. Since tests on fruit and seed fertility are currently in progress it is too early to make any statements about the responses. Segregations for the genes: a\1, c, d\1, and l\1 contributed by the esculentum parent have thus far shown no significant deviation from normal.
No barrier has been encountered in our experience thus far that would interfere to any extent with the transfer of germ plasm from S. pennellii to L. esculentum: the crosses can easily be made with every esculentum stock attempted thus far; the hybrid seeds germinate and the seedlings grow without difficulty; the hybrids are vigorous and reasonably fertile and can be selfed; seeds produced by the F1 are viable; the F2 and BC\esc generations are vigorous and sufficiently fertile for further breeding purposes. In contrast with the problems encountered with the hybrids between L. esculentum and the green-fruited tomato species, this is a delightful change.
This hybridization can unquestionably contribute a great deal to tomato genetics. Whether it has any merit for tomato breeding remains to be determined. Preliminary tests here by A. Gentile indicate no resistance of S. pennellii to the nematode species Meloidogyne incognita or M. javanica and slow infection by, but certainly not strong resistance to, Verticillium wilt. His tests also reveal resistance to Fusarium wilt. Evaluation of reactions to other diseases would be most welcome.