References Ancora, G., K. Sree Ramulu and M. Devreux. 1977. Z. Pflanzenphysiologie 82:377-388. Devreux, M., K. Sree Ramulu and D. de Nettancourt. 1976. In: Proc. Workshop European Communities -Israel on The Use of Ionizing Radiation in Agriculture, Wageningen, p. 423-431. Nettancourt, D. de, M. Devreux, U. Laneri, M. Cresti, E. Pacini, and G. Sarfatti. 1974. Theoret. Appl. Genet. 44:278- 238. Sree Ramulu, K., M. Devreux, G. Ancora and U. Laneri. 1976. Z. Pflanzenzuctg. 76:299-319. Ancora, G., F. Saccardo, M. Cappadocia, D. de Nettancourt, M. Devreux, and K. Sree Ramulu Further studies on the hybrid of Lycoperiscon esculentum cv. San Marzano Baldoni X L. peruvianum. Attempts are being made, through a joint effort at the Casaccia Center near Rome andat the University of Louvain-la-Neuve, Belgium, to obtain progenies of the self-incompatible hybrid L. esculentum var. San Marzano Baldoni X L. peruvianum (S1 S4) which was produced through embryo culture by de Nettancourt et al. (1974). The work aims at: 1) the elimination of the self- and cross-incompatibility barriers which prevent the use of the hybrid for tomato breeding, 2) the production, through anther and microspore culture, of haploids and homozygous diploids recombining certain portions of the genotypes of the two parental species, 3) the induction of amphidiploids and the analysis of their incompatibility features. In this report, we outline briefly the results recently obtained with regard to: 1) the production and analysis of back-cross progeny of the 2n esculentum X peruvianum, and 2) the breeding behavior of diploids and tetraploids derived from the cultures in vitro of anthers and stem internodes from the hybrid. 1. Backcrosses of hybrid to L. esculentum Altogether 15 different cultivars of L. esculentum have been used as pistillate parents in crosses with the hybrid. After several hundred pollinations, 3 fruits containing a total of 12 viable seeds were obtained; each fruit derived from a cross involving a different cultivar of L. esculentum as pistillate parent. The 12 plants were, as ascertained by pollen stainability, fully fertile: 10 expressed self-compatibility and the other two were self- incompatible. These 12 plants are phenotypically very different from one another and combine morphological features of the hybrid and of the parental esculentum cultivar. No fruit and no seed were obtained when the hybrid was crossed as pistillate partner to the 15 esculentum cultivars. These results indicate that: The incompatibility barrier which prevents esculentum pollen from growing through the styles of our hybrid is extremely strong. It is possible, through a choice of appropriate esculentum partners used as pistillate parents to by-pass the post-zygotic barriers which normally prevent the production of viable seeds after pollination of esculentum stigmas with hybrid pollen. 2. Breeding behavior of diploids and tetraploids regenerated from the hybrid To date, 27 diploids and 18 tetraploids, regenerated from the in vitro cultures of stem internodal segments, and 2 diploids obtained from anther cultures (Cappadocia et al. unpubl.) have been submitted to self-pollination tests, reciprocal backcrosses to the hybrid and reciprocal sib-crosses. The diploids are male and female fertile, but self-incompatible and reciprocally cross-incompatible with the hybrid. The tetraploids, as ascertained through staining tests and numerous test crosses, express relatively high pollen (more than 60% stainable pollen) and ovule fertility but are self- and cross-incompatible. No evidence whatsoever was obtained which could suggest that SC and SI alleles, when combined in a diploid hybrid pollen grain, interact with one another to produce the so-called competition effect and the subsequent breakdown of the incompatibility character which occurs in diploid S-heteroallelic peruvianum pollen (de Nettancourt, 1977).

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