Genetical and ultrastructural aspects of self and cross incompatibility in interspecific hybrids between self-compatible Lycopersicum esculentum and self-incompatible L. peruvianum

Abstract

Cytological and genetical analyses were made of the breeding system of embryo-cultured interspecific tomato hybrids between L. esculentum and L. peruvianum. It was found that fluorescence techniques and electron microscopy allowed a distinction to be made between pollen tubes inhibited by a unilateral incompatibility reaction and pollen tubes inhibited by a self-incompatibility reaction, after self-pollination of the hybrids or after reciprocal crossing between the hybrid and the parental species. The observed differences, if real and reliable, demonstrate that unilateral incompatibility in esculentum pollen tubes is governed by a single gametophytic factor which is either linked or allelic to the S-locus. This finding is discussed with reference to recent reports that unilateral incompatibility is controlled, in peruvianum styles, by a number of different dominant genes and it is concluded that these dominant genes, the S-locus of self-incompatibility and the gametophytic factor regulating the unilateral reaction in esculentum pollen belong to the same linkage group. The strong sterility barriers which prevent practically all backcrosses between the hybrid and the parental species were shown to be independent of the factors regulating stylar incompatibility. L. peruvianum is heterozygous for the sterility genes which prevent fertilization or embryo formation when the interspecific hybrid is crossed, as pistillate parent, to different accessions of L. peruvianum. One peruvianum stock was found which, as a pollinator, was highly cross-fertile with the hybrids.The presence of a concentric endoplasmic reticulum in inhibited pollen tubes was observed to be a constant feature of both the self- and the unilateral incompatibility reactions and was interpreted as an indication that incompatibility might lead to a general cessation of protein synthesis. Although incompatible tubes very much resemble, in this respect, the pollen tubes cultured in vitro, it seems probable, on theoretical grounds, that the inhibition of pollen tubes in incompatible styles does not result from an absence of growth promoting substances but from the presence of a metabolic inhibitor.

Pollen-Pistil Interactions and Their Role in Mate Selection

“…1; Lewis and Crowe, 1958;Martin, 1964;Ascher and Peloquin, 1968;Liedl et al, 1996;Covey et al, 2010). In addition, ultrastructural studies comparing SI and UI in Solanum peruvianum self-pollinations versus cross-pollinations with S. lycopersicum show that the outer (noncallose, largely pectic) pollen tube cell wall appears to thicken during SI rejection and to be degraded during UI rejection (de Nettancourt et al, 1973(de Nettancourt et al, , 1974.…”

Divergent Mating Systems and Parental Conflict as a Barrier to Hybridization in Flowering Plants

“…In most crosses between closely related self-incompatible (SI) and self-compatible (SC) plants, SI pollen grows in SC styles, but SC pollen is inhibited in SI styles (Lewis and Crowe 1958;de Nettancourt 1977). This pattern, labeled the rule by Murfett et al (1996), occurs in SI # SC taxa with gametophytic, sporophytic, and heteromorphic SI.…”

“…In general, crosses within the genus Lycopersicon conform to the rule. For ex-SI # SC ample, pollen from SC Lycopersicon esculentum fails to fertilize SI Lycopersicon peruvianum, while the reciprocal cross succeeds (Bohn 1948;Hogenboom 1972;de Nettancourt et al 1974). Similarly, L. esculentum pollen does not grow in the styles of Lycopersicon [Solanum] pennellii or of Lycopersicon hirsutum, while the reciprocal crosses successfully set seed (Rick 1960;Martin 1961bMartin , 1963Martin , 1964Liedl et al 1996).…”

The reproductive biology of the potato and its implication for breeding

“…Because this general rule is so universal, the S-gene of self-incompatibility is often assumed to be involved in the interspecific incompatibility reaction (de Nettancourt et al, 1974). However, genes other than self-incompatibility genes have also been proposed (Ascher & Peloquin, 1968;Camadro & Peloquin, 1981;Grun & Aubertin, 1966;Grun & Radlow, 1961;Martin, 1964).…”