Incompatibility In Species Research Articles

Wolbachia and host intrinsic reproductive barriers contribute additively to postmating isolation in spider mites.

Wolbachia are maternally-inherited bacteria that induce cytoplasmic incompatibility in many arthropod species. However, the ubiquity of this isolation mechanism for host speciation processes remains elusive, as only few studies have examined Wolbachia-induced incompatibilities when host populations are not genetically compatible. Here, we used three populations of two genetically differentiated colour forms of the haplodiploid spider mite Tetranychus urticae to dissect the interaction between Wolbachia-induced and host-associated incompatibilities, and their relative contribution to postmating isolation. We found that these two sources of incompatibility act through different mechanisms in an additive fashion. Host-associated incompatibility contributes 1.5 times more than Wolbachia-induced incompatibility in reducing hybrid production, the former through an overproduction of haploid sons at the expense of diploid daughters (ca. 75% decrease) and the latter by increasing the embryonic mortality of daughters (by ca. 49%). Furthermore, regardless of cross direction, we observed near-complete F1 hybrid sterility and complete F2 hybrid breakdown between populations of the two forms, but Wolbachia did not contribute to this outcome. We thus show mechanistic independence and an additive nature of host-intrinsic and Wolbachia-induced sources of isolation. Wolbachia may contribute to reproductive isolation in this system, thereby potentially affecting host differentiation and distribution in the field.

Diversification and hybrid incompatibility in auto-pseudogamous species of Mesorhabditis nematodes

BackgroundPseudogamy is a reproductive system in which females rely on the sperm of males to activate their oocytes, generally parasitizing males of other species, but do not use the sperm DNA. The nematode Mesorhabditis belari uses a specific form of pseudogamy, where females produce their own males as a source of sperm. Males develop from rare eggs with true fertilization, while females arise by gynogenesis. Males thus do not contribute their genome to the female offspring. Here, we explored the diversity of reproductive mode within the Mesorhabditis genus and addressed species barriers in pseudogamous species.ResultsTo this end, we established a collection of over 60 Mesorhabditis strains from soil and rotting vegetal matter. We found that males from pseudogamous species displayed a reduced size of their body, male tail and sperm cells compared to males of sexual Mesorhabditis species, as expected for males that face little competition. Using rDNA sequences and crosses, we could define 11 auto-pseudogamous biological species, with closely related species pairs and a possible single origin of pseudogamy in the Mesorhabditis genus. Most crosses between males and females of different species did not even produce female progeny. This surprising species barrier in pseudogamous egg activation was pre or postcopulatory depending on the species pair. In the latter case, when hybrid embryos were produced, most arrested before the first embryonic cell division. Hybrid incompatibility between auto-pseudogamous species was due to defective interaction between sperm and oocyte as well as defective reconstitution of zygotic centrosomes.ConclusionsWe established a collection of sexual and pseudo-sexual species which offer an ideal framework to explore the origin and consequences of transition to asexuality. Our results demonstrate that speciation occurs in the pseudogamous state. Whereas genomic conflicts are responsible for hybrid incompatibility in sexual species, we here reveal that centrosomes constitute key organelles in the establishment of species barrier.

Incompatibilidade de enxertia em Prunus

A incompatibilidade de enxertia é um problema que, além de prejuízo econômico aos produtores, causa atraso no lançamento de novas cultivares-copa e portaenxertos, devido ao longo período de tempo necessário para os testes de compatibilidade. O objetivo desta revisão é fazer um apanhado das principais e mais relevantes pesquisas realizadas envolvendo o tema incompatibilidade de enxertia em espécies frutíferas, especialmente as do gênero Prunus. Incompatibilidade é um fenômeno extremamente complexo, que envolve interações anatômicas, fisiológicas, bioquímicas e moleculares entre a cultivar-copa e o portaenxerto. Sendo, por essa razão, um problema de difícil estudo. Porém, acredita-se que através de uma análise conjunta dos diversos mecanismos de incompatibilidade, se pode avançar mais rapidamente no entendimento deste fenômeno.

Interactions of hybridization and mating systems: A case study in Leptosiphon (Polemoniaceae)

The roles of hybridization and mating systems in the evolution of angiosperms have been well studied, but less work has focused on their interactions. Self-incompatible and self-compatible species often show asymmetry in heterospecific pollen rejection. Self-fertilization can preempt ovules before opportunities for hybridization. In turn, hybridization might affect mating system evolution through selection for selfing to avoid production of low fitness hybrids. • AFLP and morphological analyses were used to test for hybrids in a contact zone between species with contrasting breeding systems. Crossing experiments examined the relative contributions to reproductive isolation of pollen-pistil interactions, timing of self-fertilization, and F1 viability and fertility. A diallel cross of siblings tested for an association between heterospecific incompatibility and S-genotype in the self-incompatible species. • A low frequency of hybrids was detected in the contact zone. Pollen-pistil interactions were partially consistent with the SI × SC rule; some individuals of the self-incompatible species rejected heterospecific pollen, whereas the self-compatible species was fully receptive to it. In the selfing species, individuals with early selfing produced fewer hybrid progeny than did those with delayed self-compatibility when heterospecific pollen was applied after self-pollen. Viability of F1s was high but fertility was low. Variability in heterospecific pollen rejection was not related to S-genotype. • Both self-fertilization and self-incompatibility are associated with limits to hybridization at this site. The strong effect of timing of selfing on production of low fitness F1s suggests that hybridization might select for early selfing in this population.

Genetic incompatibility drives mate choice in a parasitic wasp

IntroductionAllelic incompatibility between individuals of the same species should select for mate choice based on the genetic make-up of both partners at loci that influence offspring fitness. As a consequence, mate choice may be an important driver of allelic diversity. A complementary sex determination (CSD) system is responsible for intraspecific allelic incompatibility in many species of ants, bees, and wasps. CSD may thus favour disassortative mating and in this, resembles the MHC of the vertebrate immune system, or the self-incompatibility (SI) system of higher plants.ResultsHere we show that in the monogamous parasitic wasp Bracon brevicornis (Wesmael), females are able to reject partners with incompatible alleles. Forcing females to accept initially rejected partners resulted in sex ratio distortion and partial infertility of offspring.ConclusionsCSD-disassortative mating occurred independent of kin recognition and inbreeding avoidance in our experiment. The fitness consequences of mate choice are directly observable, not influenced by environmental effects, and more severe than in comparable systems (SI or MHC), on individuals as well as at the population level. Our results thus demonstrate the strong potential of female mate choice for maintaining high offspring fitness in this species.

Cardinium is associated with reproductive incompatibility in the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae)

Cardinium, a bacterium from the Bacteroidetes group, is associated with reproductive manipulations such as cytoplasmic incompatibility, parthenogenesis, and feminization in some arthropod species. We, and others, have shown that Cardinium, but not Wolbachia, is an endosymbiont in some populations of Metaseiulus occidentalis, a phytoseiid mite that is an important predator of spider mite pests of agricultural crops. However, the precise biological effects that Cardinium may have on M. occidentalis remain unclear. In this study we show, in two sets of crosses between different colonies of Cardinium-free (C−) M. occidentalis females and Cardinium-containing (C+) males, that fecundity was reduced in parental females, F1 progeny survival rates were reduced, and fewer female progeny were produced when compared to the reciprocal and control crosses. There were no differences in these attributes in the reciprocal and two control crosses. Cardinium was transmitted maternally but there was no observed paternal transmission. Finally, Cardinium did not cause asexual (thelytoky) reproduction in M. occidentalis. Thus, Cardinium is associated with nonreciprocal reproductive incompatibility in M. occidentalis and our results support the hypothesis that Cardinium is a reproductive parasite in this agriculturally important predator. Cardinium may therefore affect the evolution and ecology of M. occidentalis and biological control efforts using this mite.

Sexual incompatibility in Rosaceae fruit tree species: molecular interactions and evolutionary dynamics

Fruit crops have a growing economic importance worldwide and molecular genetics might be useful in solving many problems that arise during commercial production. One of the fields that have attracted intense attention is the molecular basis of self-incompatibility that may result in low fruit set. In tree fruits of the Rosaceae family, the incompatibility reactions take place between the pistil S-ribonuclease (S-RNase) and the pollen-expressed S-haplotype specific F-box (SFB) proteins. In most cases, the loss of self-incompatibility was associated with mutations in the S-RNase or SFB genes. A total of 27 non-functional S-haplotypes have been identified and characterized, most (24) of which emerged as a consequence of natural mutations. In the Prunoideae, most haplotypes are pollen-part mutants (50 %), while 8 are stylar-part mutants (36 %), one haplotype shows both pollen- and stylar-part mutations, and molecular changes for two haplotypes still have not been clarified. In contrast, non-functional natural haplotypes in the Maloideae are all stylar-part mutants. The analysis of such mutants may shed light on underlying molecular mechanisms as was the case with the establishment of the general inhibitor model that describes interactions between pollen and pistil S-proteins. However, several other molecules were supposed to contribute to the molecular interactions, at least in Solanaceae, a family with a similar self-incompatibility system. This review also endeavours to delineate the evolutionary implications of the S-locus mutations and collect limited data on non-S-locus molecular interactions and signaling events after self- and cross-pollination of fruit tree species.

Sexual incompatibility in Rosaceae fruit tree species: molecular interactions and evolutionary dynamics

Fruit crops have a growing economic importance worldwide and molecular genetics might be useful in solving many problems that arise during commercial production. One of the fields that have attracted intense attention is the molecular basis of self-incompatibility that may result in low fruit set. In tree fruits of the Rosaceae family, the incompatibility reactions take place between the pistil S-ribonuclease (S-RNase) and the pollen-expressed S-haplotype specific F-box (SFB) proteins. In most cases, the loss of self-incompatibility was associated with mutations in the S-RNase or SFB genes. A total of 27 non-functional S-haplotypes have been identified and characterized, most (24) of which emerged as a consequence of natural mutations. In the Prunoideae, most haplotypes are pollen-part mutants (50 %), while 8 are stylar-part mutants (36 %), one haplotype shows both pollen- and stylar-part mutations, and molecular changes for two haplotypes still have not been clarified. In contrast, non-functional natural haplotypes in the Maloideae are all stylar-part mutants. The analysis of such mutants may shed light on underlying molecular mechanisms as was the case with the establishment of the general inhibitor model that describes interactions between pollen and pistil S-proteins. However, several other molecules were supposed to contribute to the molecular interactions, at least in Solanaceae, a family with a similar self-incompatibility system. This review also endeavours to delineate the evolutionary implications of the S-locus mutations and collect limited data on non-S-locus molecular interactions and signaling events after self- and cross-pollination of fruit tree species.

Effect of intracellular Wolbachia on interspecific crosses between Drosophila melanogaster and Drosophila simulans

Wolbachia are bacteria that live inside the cells of a large number of invertebrate hosts and are transmitted from infected females to their offspring. Their presence is associated with cytoplasmic incompatibility in several species of Drosophila. Cytoplasmic incompatibility results when the sperm of infected males fertilize eggs of uninfected females, causing more or less intense embryonic mortality (unidirectional incompatibility). This phenomenon also appears in crosses between populations infected with different Wolbachia strains (bidirectional incompatibility). The influence of Wolbachia infection on host populations has attracted attention as a potentially rapid mechanism for development of reproductive isolation and subsequent speciation. We examined the influence of this bacterium on reproductive isolation in interspecific crosses between Drosophila melanogaster and D. simulans. We found that Wolbachia infection negatively affected these two species in homospecific crosses. However, in interspecific crosses, it only influenced sexual isolation, as infected females more frequently hybridized than females free of infection; postzygotic reduction of fitness (bidirectional cytoplasmic incompatibility) was not detected. This would be explained by the existence of several modes of rescue systems in these two species, reducing cytoplasmic incompatibility between them. Wolbachia does not appear to cause reproductive isolation between these two species.

Wolbachia-induced cytoplasmic incompatibility in Japanese populations of Tetranychus urticae (Acari: Tetranychidae)

Intracellular bacteria of the genus Wolbachia (alpha Proteobacteria) induce cytoplasmic incompatibility (CI) in many arthropod species, including spider mites, but not all Wolbachia cause CI. In spider mites CI becomes apparent by a reduced egg hatchability and a lower daughter:son ratio: CI in haplodiploid organisms in general was expected to produce all-male offspring or a male-biased sex ratio without any death of eggs. In a previous study of Japanese populations of Tetranychus urticae, two out of three green-form populations tested were infected with non-CI Wolbachia strains, whereas none of six red-form populations harbored Wolbachia. As the survey of Wolbachia infection in T. urticae is still fragmentary in Japan, we checked Wolbachia infection in thirty green-form populations and 29 red-form populations collected from a wide range of Japanese islands. For Wolbachia-infected populations, we tested the effects of Wolbachia on the reproductive traits and determined the phylogenetic relationships of the different strains of Wolbachia. All but one green-form populations were infected with Wolbachia and all strains belonged to the subgroup Ori when the wsp gene was used to determine the phylogenetic relationships of different strains of Wolbachia. Six out of 29 red-form populations harbored Wolbachia and the infected strains belonged to the subgroups Ori and Bugs. Twenty-four of 29 infected green-form populations and five of six infected red-form populations induced CI among the hosts. Thus, CI-Wolbachia strains are widespread in Japan, and no geographical trend was observed in the CI-Wolbachia. Although three red-form populations harbored other intracellular bacteria Cardinium, they did not affect host reproduction.

Multiple infections and diversity of cytoplasmic incompatibility in a haplodiploid species

Cytoplasmic incompatibility (CI) is a sperm-egg incompatibility commonly induced by the intracellular endosymbiont bacterium Wolbachia that, in diploid species, results in embryo mortality. In haplodiploid species, two types of CI exist depending on whether the incompatible fertilized eggs develop into males (male development (MD)) or abort (female mortality (FM)). CI allows multiple infections to be maintained in host populations, and thus allows interactions to occur between co-infecting strains. In Leptopilina heterotoma, three Wolbachia strains coexist naturally (wLhet1, wLhet2, wLhet3). When these three strains are all present, they induce a CI of FM type, whereas wLhet1 alone expresses a CI phenotype intermediate between MD and FM. Here, we compare CI effects in crosses involving insect lines sharing the same nuclear background, but harboring different mixtures of strains. Mating experiments showed that: (i) wLhet2 and wLhet3 also induce an intermediate CI when acting alone, and show a bidirectional incompatibility; (ii) there is no interaction between the co-infecting strains in CI expression; (iii) the diversity of Wolbachia present within a male host influences the expression of CI: an increase in the number of strains is correlated with a decrease in the proportion of the MD type, which is also correlated with an increase in bacterial density. All these data suggest that the CI of FM type results from a stronger effect than the MD type, which conflicts with the conventional hypotheses used to explain CI diversity in haplodiploids, and could provide some new information about CI mechanisms in insects.

Infection density of Wolbachia and incompatibility level in two planthopper species, Laodelphax striatellus and Sogatella furcifera

Wolbachia, a bacterial endosymbiote of arthropods, causes cytoplasmic incompatibility (CI) in many insect species. CI traits were studied in two planthopper species, Laodelphax striatellus and Sogatella furcifera, and Wolbachia densities in these planthopper species were calculated by quantitative PCR methods. The CI level of L. striatellus was quite high and even aged males strongly caused CI. In contrast, S. furcifera showed partial CI, and males lost their ability to cause CI with age. Wolbachia infecting these two planthopper species were the same with respect to the nucleotide sequences of Wolbachia genes, 16S rDNA, ftsZ gene, groE genes, and wsp gene. Two methods for quantitative PCR, one using a DNA sequencer and the other a real-time sequence detection system, were established to calculate the amount of Wolbachia in the planthoppers. The density of Wolbachia in S. furcifera males was quite low. The difference in CI levels between the two planthopper species seems to be due to different amounts of Wolbachia infecting males.

Wolbachia neither induces nor suppresses transcripts encoding antimicrobial peptides.

Wolbachia are intracellular maternally inherited microorganisms that are associated with reproductive abnormalities such as cytoplasmic incompatibility (CI), feminization and parthenogenesis in the various arthropod species they infect. Surveys indicate that these bacteria infect more than 16% of all insect species as well as isopods, mites and nematodes, making Wolbachia one of the most ubiquitous parasites yet described. However, nothing is known about the interactions of this bacterium with the host's immune system. We studied the expression of inducible antimicrobial markers in the adults of two Wolbachia infected insect species, Drosophila simulans and Aedes albopictus. The lack of available immune markers in the mosquito species led us to clone part of the defensin gene from this species, which was found to be very similar to the other mosquito defensins cloned from Anopheles gambiae and Aedes aegypti. Comparisons of the expression pattern of the antibacterial markers between Wolbachia-infected and cured lines, and also between bacteria-challenged and unchallenged adults indicated that Wolbachia does not either constitutively induce or suppress the transcription of these antibacterial genes. In addition, no difference in the transcription of these genes was found between double and single Wolbachia-infected strains or between strains in which Wolbachia has different tissue tropisms.

Wolbachia transfer from Drosophila melanogaster into D. simulans: Host effect and cytoplasmic incompatibility relationships.

Wolbachia are maternally transmitted endocellular bacteria causing a reproductive incompatibility called cytoplasmic incompatibility (CI) in several arthropod species, including Drosophila. CI results in embryonic mortality in incompatible crosses. The only bacterial strain known to infect Drosophila melanogaster (wDm) was transferred from a D. melanogaster isofemale line into uninfected D. simulans isofemale lines by embryo microinjections. Males from the resulting transinfected lines induce >98% embryonic mortality when crossed with uninfected D. simulans females. In contrast, males from the donor D. melanogaster line induce only 18-32% CI on average when crossed with uninfected D. melanogaster females. Transinfected D. simulans lines do not differ from the D. melanogaster donor line in the Wolbachia load found in the embryo or in the total bacterial load of young males. However, >80% of cysts are infected by Wolbachia in the testes of young transinfected males, whereas only 8% of cysts are infected in young males from the D. melanogaster donor isofemale line. This difference might be caused by physiological differences between hosts, but it might also involve tissue-specific control of Wolbachia density by D. melanogaster. The wDm-transinfected D. simulans lines are unidirectionally incompatible with strains infected by the non-CI expressor Wolbachia strains wKi, wMau, or wAu, and they are bidirectionally incompatible with strains infected by the CI-expressor Wolbachia strains wHa or wNo. However, wDm-infected males do not induce CI toward females infected by the CI-expressor strain wRi, which is found in D. simulans continental populations, while wRi-infected males induce partial CI toward wDm-infected females. This peculiar asymmetrical pattern could reflect an ongoing divergence between the CI mechanisms of wRi and wDm. It would also confirm other results indicating that the factor responsible for CI induction in males is distinct from the factor responsible for CI rescue in females.

Implications of phenolic compounds in graft incompatibility in fruit tree species

Cultivar stability in fruit tree species is ensured by grafting on particular rootstocks and a fruit tree can be considered as a symbiosis between scion and rootstock. However, heterospecific grafts are often incompatible resulting in death of the tree. The causes of graft incompatibility remain still unknown, although many biochemical events are affected. Phenol compounds play an important role in plants and constitute an important group in scion–rootstock relations. In this review, their implications in the mechanism of the incompatibility in the early steps of graft establishment have been reviewed with the aim of providing a framework for an early detection of incompatible grafts to increase the efficiency in rootstock breeding.

Wolbachia, normally a symbiont of Drosophila, can be virulent, causing degeneration and early death.

Wolbachia, a maternally transmitted microorganism of the Rickettsial family, is known to cause cytoplasmic incompatibility, parthenogenesis, or feminization in various insect species. The bacterium-host relationship is usually symbiotic: incompatibility between infected males and uninfected females can enhance reproductive isolation and evolution, whereas the other mechanisms enhance progeny production. We have discovered a variant Wolbachia carried by Drosophila melanogaster in which this cozy relationship is abrogated. Although quiescent during the fly's development, it begins massive proliferation in the adult, causing widespread degeneration of tissues, including brain, retina, and muscle, culminating in early death. Tetracycline treatment of carrier flies eliminates both the bacteria and the degeneration, restoring normal life-span. The 16s rDNA sequence is over 98% identical to Wolbachia known from other insects. Examination of laboratory strains of D. melanogaster commonly used in genetic experiments reveals that a large proportion actually carry Wolbachia in a nonvirulent form, which might affect their longevity and behavior.

Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex.

Maternally inherited bacteria of the genus Wolbachia are responsible for the early death of embryos in crosses between uninfected females and infected males in several insect species. This phenomenon, known as cytoplasmic incompatibility, also occurs between strains infected by different symbionts in some species, including Drosophila simulans. Wolbachia was found in two species closely related to D. simulans, Drosophila mauritiana, and Drosophila sechellia, and shown to cause incompatibility in the latter species but not in D. mauritiana. Comparison of bacterial and mtDNA history clarifies the origins of bacterial and incompatibility polymorphisms in D. simulans. Infection in D. mauritiana is probably the result of introgression of an infected D. simulans cytoplasm. Some D. simulans and D. sechellia cytoplasmic lineages harbor two bacteria as a consequence of a double infection which probably occurred in a common ancestor. The descendant symbionts in each species are associated with similar incompatibility relationships, which suggests that little variation of incompatibility types has occurred within maternal lineages beyond that related to the density of symbionts in their hosts.

Population genetics of filamentous fungi

Population genetics aims to understand causes and consequences of the genetic structure of populations, i.e. distributions of genetic variants in space and time. Among the most important determinants of the genetic population structure is the genetic system itself, which is the collection of processes and mechanisms responsible for the transmission of genetic information. Filamentous fungi offer excellent opportunities for studying the effects of the genetic system on genetic population structure. Apart from their advantage as laboratory organisms, they exhibit a wide variety of genetic systems. In particular, their inherent capacity for anastomosis provides unique possibilities for investigating rates and consequences of horizontal gene transfer. Furthermore, the temporary confinement of the products of meiosis in a common structure (the ascus) enables the study of competitive and antagonistic interactions between the meiotic products. An intriguing example of the latter is the phenomenon of 'spore killing', resulting in distorted meiotic segregation. This paper concentrates on population level research of the occurrence of vegetative incompatibility in Aspergillus and Neurospora species and to what extent this will inhibit horizontal transmission of genetic information, and on spore killing in Podospora anserina.

Genetic analysis of incompatibility in the diploid Ipomoea species closely related to the sweet potato

In order to identify the genotypic constitutions of incompatibility in the diploid species, Ipomoea leucantha Jacq. (K221), which is most closely related to the sweet potato, the progenies derived from the reciprocal crosses, backcrosses and testcrosses were analysed. All the plants examined were self-incompatible, and pollen germination was inhibited on the stigma after incompatible pollinations. No reciprocal differences were found in the incompatibility reactions. In the progenies three incompatibility groups were observed which showed the rather simple segregation ratios. The homozygous plants for incompatibility alleles were obtained in the progenies. The experimental results demonstrated a sporophytic type of incompatibility controlled by a single locus with multiple S-alleles exhibiting a dominance relationship in both the pollen and the stigma. The plants obtained in the progenies had the following genotypes: S 1 S 2, S 1 S 3, S 2 S 2, S 2 S 3 and S 3 S 3.

INTERSPECIFIC INCOMPATIBILITY IN SOLANUM SPECIES

Pandey, K.K. (Crop Res. Div., D.S. & I.R., Lincoln, Christchurch, New Zealand.) Interspecific incompatibility in Solanum species. Amer. Jour. Bot. 49(8): 874–882. Illus. 1962.—A diallel cross involving 11 self‐incompatible and 3 self‐compatible species of Solanum was made to study the genetic basis of interspecific incompatibility. Interspecific incompatibility was not limited to crosses in which a self‐compatible species was used as the male parent onto a self‐incompatible species (unilateral incompatibility). A number of crosses between self‐incompatible species were incompatible. In one cross, Q vernei X verrucosum, a self‐compatible species was successful as a pollen parent with a self‐incompatible species. Unlike other hybrids between self‐compatible and self‐incompatible species, which are self‐incompatible, these F1 hybrids were self‐fertile, and cross‐fertile among themselves and with both parents. The self‐fertile S. polyadenium was cross‐incompatible as a female as well as a male parent with all other species. It is suggested that the unilateral incompatibility is a property of the allele SC which originated as a consequence of one kind of breakdown of the SI gene; the SC allele produces “bare” pollen growth substances which are inactivated in an incompatible style. It is proposed that the failure of the principle of unilateral interspecific incompatibility in solanaceous species may be due to the action of alleles at the second incompatibility locus revealed in certain Mexican species. It is assumed that the South American species are selected intraspecifically only for the action of S alleles but that in certain interspecific crosses and rarely in intraspecific crosses the alleles at the second locus may be expressed, thus interfering with the usual action of S alleles. The F1 hybrids Q verrucosum (self‐fertile) X simplicifolium (self‐sterile) were self‐incompatible at the tetraploid as well as the diploid level, and their cross‐compatibility behavior was consistent with the expected activity of the SC and SI alleles of the 2 parents respectively.