INCOMPATIBILITY IN AMSINCKIA GRANDIFLORA (BORAGINACEAE): DISTRIBUTION OF CALLOSE PLUGS AND POLLEN TUBES FOLLOWING INTER- AND INTRAMORPH CROSSES

The distribution of callose plugs and pollen tubes was investigated following inter- and intramorph crosses of Amsinckia grandiflora (Boraginaceae), a distylous species possessing cryptic self-incompatibility. Callose plug distribution provided a good indication of the distribution of pollen tubes. Compared to intramorph crosses, many more callose plugs and pollen tubes were found in basal stylar regions following intermorph crosses, indicating that differential pollen tube growth is a likely cause of cryptic self-incompatibility. The incompatibility response differed for the floral morphs: in the pin (long-styled) morph pollen tubes were most likely to cease growth in the midstylar region, while inhibition was more likely to occur in the upper stylar region of the thrum (short-styled) morph. There was no evidence of stigmatic inhibition of pollen tubes for either morph, although the incompatibility response in the Boraginaceae is normally located in the stigmatic region.     

Fecundity and fitness in cross-compatible pollinations of tristylous North American Lythrum salicaria populations

As heterostyly and self incompatibility are linked in tristylous L. salicaria, all cross-compatible pollinations – those between anthers and styles of the same level – should produce viable seed. The rigor of this theory was tested using seed set and germination of cross-compatible pollinations in 18 naturalized L. salicaria populations in Minnesota/Wisconsin (n=342 genotypes; n=86 shorts, n=127 mids, and n=129 longs). Seed set for short-styled genotypes ranged from zero to 135 (36+38); mids–0–156, (53+39), and longs–0–151 (59+39). Mean seed set per capsule was not significantly different for mids and longs, but both were significantly greater than that of shorts (F=14, P<0.0001). Zero seed set frequently occurred in most compatible crosses, in contrast with theoretical expectations. The high percentage of populations deviating from normality must be due to incompatibility. An incompatibility system independent of heterostyly could cause this, where failed crosses result from matches of incompatibility specificities in pollen and pistil. This independence is questionable, however, given the non-significant difference in failed outcrosses for pooled χ² comparing within and between populations (χ²=0.395, P>0.5). A sporophytic incompatibility model is proposed with a minimum of three specificities. Zero seed set in compatible crosses is due to the addition of alleles from L. alatum, a distylous species that forms introgressive hybrids with L. salicaria. Reduced fecundity could increase the deficiency of shorts, and significantly greater seed germination of shorts could explain the continued presence of short-styled individuals in L. salicaria populations. Received: 3 February 2000 / Accepted: 25 March 2000     

Identification of self-incompatibility groups in<Emphasis Type="Italic"> Hatiora</Emphasis> and<Emphasis Type="Italic"> Schlumbergera</Emphasis> (Cactaceae)

The Cactaceae, a family of about 1,800 species of succulent perennials, contains numerous species that exhibit self-incompatibility (SI). The objective of the current study was to determine the number of incompatibility groups present among diploid (2n=2x=22) cultivars of the genera Schlumbergera Lem. (Christmas cacti) and Hatiora Britton & Rose (Easter cacti). Two partial diallel crosses were performed, one with 19 cultivars of Christmas cacti [= S. truncata (Haworth) Moran and S. × buckleyi (Buckley) Tjaden] and the other with 10 cultivars of Easter cacti [= H. gaertneri (Regel) Barthlott, H. rosea (Lagerheim) Barthlott, and H. × graeseri Barthlott ex D. Hunt]. The compatibility/incompatibility status of crosses was determined by percent fruit set and presence of seed in mature fruit. None of the cultivars set fruit when selfed or crossed with a cultivar in the same incompatibility group, but fruit set ranged from 35% to 100% following compatible crosses. For the Christmas cacti, eight intra-incompatible but reciprocally compatible groups were identified, with 13 of the 19 cultivars assigned to three incompatibility groups (68%). The ten cultivars of Easter cacti yielded nine intra-incompatible but reciprocally compatible groups, with two cultivars in one incompatibility group and the other eight cultivars each assigned to a unique group. One cultivar of Christmas cactus ('Abendroth 6') was incompatible when crossed as a male with cultivars in incompatibility group 2 but was compatible in reciprocal crosses, results that suggest that this cultivar is an S-allele homozygote. The crossing relationships are consistent with a one-locus, gametophytic SI system with multiple alleles. Allozyme locus Lap-1, shown previously to be linked with the S locus (recombination frequency 7%) in Schlumbergera, exhibited insufficient allelic diversity for determining the S genotypes of the 19 cultivars of Christmas cacti. Based on the number of incompatibility groups in each diallel, at least five S-alleles occur in the 19 Christmas cacti and the 10 Easter cacti.Publication 3337 of the Massachusetts Agricultural Experiment Station. This material is based on work supported in part by the Cooperative State Research, Extension, Education Service, United States Department of Agriculture, Massachusetts Agricultural Experiment Station, under Project No. 746     

Genetic Differentiation in Tetranychus Urticae (Acari: Tetranychidae): polymorphism,host races or sibling species?

Based on allozyme electrophoresis at the Pgm locus and nuclear ribosomal DNA (ITS2) sequences, we studied the genetic variation of the two-spotted spider mite Tetranychus urticae Koch collected on rose bay, Nerium oleander L. (Apocynaceae), from several localities around the Mediterranean basin. In addition, we compared these results with those of Navajas et al. (1998) and Tsagkarakou (1997) who collected from several other host plants from the Mediterranean. In the western part of this area (Spain, France, Tunisia), we found the individuals collected from rose bay to be clearly genetically differentiated from other samples. No evidence of such host-associated differentiation was detected in the eastern Mediterranean (Italy and Greece). The genetic differentiation of mites collected on rose bay was investigated further by studying the reproductive incompatibilities between populations in Greece and in France and a laboratory strain reared on bean, Phaseolus vulgaris, in France. Reciprocal crosses performed between these strains revealed variable levels of incompatibility, spanning from partial to complete reproductive isolation. In all cases incompatibility was asymmetric. We designed a test based on double-mating to establish the fertilization status of females in fully incompatible crosses. These crosses showed that the females had been inseminated, which suggests that the barrier to reproduction is not of a prezygotic behavioral nature. The data raises the question of the relative role of ecological factors (host plant) and geographical distance, in the ongoing differentiation process potentially leading to speciation.     

Distyly and heteromorphic incompatibility in oceanic island species ofErythroxylum (Erythroxylaceae)

Surveys of oceanic island floras have shown that heterostyly is usually absent in such regions, probably because this floral polymorphism is often associated with a self-incompatibility system. In this context we describe the floral biology of three species ofErythroxylum on La Réunion island and examine the compatibility relationships of one of these species,E. laurifolium. All three species are distylous but differ in relative stigma-anther separation in the different morphs. In general, short-styled flowers have greater stigma-anther separation than long-styled flowers, which are often homostylous in appearance. This lack of stigma-anther separation in long-styled flowers is due to style twisting which improves reciprocity at the high organ level. The reduced stigma-anther separation does not appear to be associated with the evolution of selfing asErythroxylum laurifolium shows heteromorphic self-incompatibility. The presence of heteromorphic incompatibility in a group of species that have colonized an oceanic island is discussed.     

Pollen flow between flowers of the same morph in invasive populations of Oxalis pes-caprae L. in the western Mediterranean region

Oxalis pes-caprae is a tristylous South African geophyte that is invasive in regions with Mediterranean climate. Given the introduction of the short-styled morph only, vegetative reproduction was, until recently, the reproductive mode known for this invaded area. The detection of new floral morphs, fruit and seed production in natural populations of the invaded range, together with the reported weakening in the heteromorphic incompatibility system, raised the question on whether the short-styled flowers are able to exchange pollen among themselves, and if so, which mechanisms account for it. Thus, flower morphometric analysis and field experiments were conducted to assess pollinator visitation rates and pollen flow in three invasive populations. Flower morphological changes suggesting the evolution from tristyly towards semi-homostyly were observed. Moreover, O. pes-caprae flowers were visited by different functional groups of pollinators, mostly hymenopteran. Dye flow experiments revealed that the short-styled flowers were able to successfully exchange pollen among themselves in natural conditions. All of this, together with the weakening of the incompatibility system, constitutes further data that might help to explain the recently reported occurrence of sexual reproduction in this invaded range, which by itself bears important implications for the invasion process of O. pes-caprae.     

Unilateral incompatibility within the brassicaceae: further evidence for the involvement of the self-incompatibility (S)-locus

Unilateral pollen-pistil incompatibility within the Brassicaceae has been re-examined in a series of interspecific and intergeneric crosses using 13 self-compatible (SC, Sc) species and 12 self-incompatible (SI) species from ten tribes. SC x SC crosses were usually compatible, SI x SC crosses showed unilateral incompatibility, while SI x SI crosses were often incompatible or unilaterally incompatible. Unilateral incompatibility (UI) is shown to be overcome by bud pollination or treating stigmas with cycloheximide — features in common with self-incompatibility. Treating stigmas with pronase prevents pollen tubes from penetrating the stigma in normally compatible intra-and interspecific pollinations. The results presented show that the presence of an incompatibility system is important in predicting the outcome of interspecific and intergeneric crosses and, combined with the physiological similarities between UI and SI, would suggest an involvement of the S-locus in UI.     

Inheritance of spontaneous mutant homostyles in Turnera subulata x krapovickasii and in autotetraploid T. scabra (Turneraceae)

To explore the genetic architecture of distyly in Turnera spp., we determined the inheritance and compatibility behaviour of two spontaneous homostyled mutants. A long-homostyled mutant shoot arose on an otherwise short-styled plant that was an artificial hybrid (Turnera subulata x T. krapovickasii) between two diploid distylous species. The mutation appears to be an allele, SH, of the distyly locus with the dominance relationships, S>SH>s, where S confers the short-styled phenotype, SH confers homostyly in SHSH and SHs genotypes, and ss genotypes are long-styled. Aberrant segregation ratios were observed among some crosses and might be the result of pollen competition. Compatibility relationships are consistent with the hypothesis that a gene complex determines distyly. Infrequently, revertant short-styled flowers have appeared on cuttings of the T. subulata x T. krapovickasii mutant and on occasion, short-styled progeny have appeared in crosses where none were expected. A second mutant homostyle was discovered in autotetraploid T. scabra. The mutation is inherited as above, however, tetrasomic inheritance occurs at the locus. This homostyled mutant carries two copies of the SH allele and has the duplex genotype SHSHss. Compatibility relationships were as observed above. The occurrence of homostyled mutants is consistent with the hypothesis that a linked gene complex underlies the inheritance of distyly in Turnera but we cannot discount the hypothesis that an allelic series is responsible.     

Trimorphic incompatibility in Eichhornia azurea (Pontederiaceae)

Eichhornia azurea (Pontederiaceae) is a mat-forming, clonal aquatic that inhabits lakes, marshes and river systems in many parts of the Neotropics. The species is tristylous with long-, mid-, and short-styled morphs commonly represented in natural populations. To investigate whether E. azurea possesses a trimorphic incompatibility system typical of tristylous species, we conducted a controlled pollination experiment on 15 clones representing the three style morphs from a natural population near Rosario, Argentina. Comparisons of fruit and seed set following self-, illegitimate, and legitimate pollinations clearly demonstrated the presence of trimorphic incompatibility in E. azurea. Self- and illegitimate pollinations produced significantly less fruit and seed than legitimate pollinations in all three style morphs. Pollen from the two anther levels within a flower exhibited contrasting compatibility relations in self-pollinations. In common with several other tristylous species in Pontederiaceae, the expression of self-incompatibility was weakest in the mid-styled morph and strongest in the short-styled morph. We discuss the ecological and evolutionary significance of the partial expression of trimorphic incompatibility in E. azurea. Received: 3 May 1999 / Revision accepted: 27 July 1999     

Cross-incompatibility between two sympatric polyploid Solanum species

Summary Preliminary results from a large number of reciprocal crosses between the closely related sympatric species S. gourlayi Hawkes (2n=4x=48) and S. oplocense Hawkes (2n=6x=72) indicated that they are difficult to hybridize. Pollen-pistil incompatibility barriers were detected via fluorescent microscopy. The cross incompatibility reaction occurred at three sites in 6x×4x crosses; on the stigma, in the first one-third of the style, and in the first two-thirds of the style. In the reciprocal 4x×6x crosses the incompatibility reaction invariably occurred in the ovary. Backcrosses of interspecific pentaploid hybrids (that were occasionally formed) to both parental populations were fully compatible, partially compatible, and fully incompatible with three sites of cross-incompatibility reaction similar to those observed in 6x×4x crosses, respectively. Both polyploid species were found to be selfcompatible, whereas their F1 hybrids were found to be self-incompatible. An hypothesis based on interactions of dominant cross-incompatibility (CI) genes in pistils and dominant specific complementary genes in pollen grains is postulated to explain these observations. The cross-incompatibility system that appears to be operating in nature between 4x S. gourlayi and 6x S. oplocense provides a way for gene exchange between sympatric populations without threatening the identity of either species.     

Linkage between an incompatibility locus and a peroxidase isozyme locus (Prx 7) in rye

Summary Under controlled growth chamber conditions of 30 °C, seed set after selfing is possible in normally self-incompatible rye plants. Within selfed progenies produced by this method, plants homozygous at the peroxidase isozyme locus Prx 7 were crossed to heterozygous individuals. Segregation at the Prx 7 locus in progenies of these crosses provides clear evidence of a close linkage between Prx 7 and one of the two incompatibility loci in rye. A recombination fraction in the range of 0–2% was calculated from the segregation data. In rye, Prx 7 is linked with a phosphoglucoisomerase locus (Pgi). The similarity between the observations in Secale cereale and those made in Lolium perenne is discussed.     

Flexible mating system in distylous populations of <Emphasis Type="Italic">Psychotria carthagenensis</Emphasis> Jacq. (Rubiaceae) in Brazilian Cerrado

In family Rubiaceae distyly is very common, and large variation in heterostyly characteristics has been previously documented. Analysis of these variations, even within a species, is very useful to our understanding of the evolutionary process that caused this polymorphism. For this reason, the goal of this study is to investigate the floral morphology and diallelic incompatibility system of three populations of Psychotria carthagenensis. The three studied populations of P. carthagenensis occur in forest fragments in protected areas in an urban matrix in the Municipality of Campo Grande, Mato Grosso do Sul State, Brazil. Reciprocal position of style length and stamen height was found in populations, and in general short-styled flowers were larger than long-styled flowers. All populations presented 1:1 morph ratio between short-styled and long-styled flowers. Regarding breeding system, flowers of P. carthagenensis were self-compatible and compatible within plants of the same morph, and there was no pollen limitation in the populations in any case. In only one of the populations were there differences in the extent of compatibility between morphs, with the long-styled morph being more self-compatible than the short-styled morph. The reproductive strategy of these populations can be advantageous in case of fluctuation of pollinator activity.     

Parasexual analysis of common-A crosses in the basidiomycete Agrocybe aegerita

Summary Crosses were performed between homokaryons of Agrocybe aegerita having the same allele at the A incompatibility gene but different B alleles. Heterokaryotic mycelia originating from crosses between two complementary auxotrophs were characterized by their instability on complete medium and extensive anastomosis between hyphae. Diploid mycelia were selected by plating oidia recovered from these heterokaryons onto minimal medium. These mycelia were characterized by the production of larger oidia than those of homokaryons, the release of a brown pigment when growing on complete medium and extensive hyphal anastomoses. Diploids retained the two B incompatibility functions of their homokaryotic parents and gave rise to a diploid/haploid dikaryon when crossed with a compatible homokaryon. Nearly 1% of the oidia recovered from heterokaryons were diploid. These nuclear fusion frequencies as well as the production of brown pigments enabled the identification of diploid strains on complete medium. In this way, crosses between wild prototrophic strains were successfully performed. Somatic recombination was induced following the treatment of diploid mycelia with haploidizing compounds. Selection based on the inability of mycelia to produce the brown pigments on complete medium led to selection of strains homoallelic at the B locus.     

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 S_C which originated as a consequence of one kind of breakdown of the S_I gene; the S_C 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 S_C and S_I alleles of the 2 parents respectively.     

Inheritance and genetic mapping of self-incompatibility in Coffea canephora Pierre

Cross-compatibility behaviour of doubled haploid (DH) and hybrid genotypes of Coffea camphora was established using both phenotypic bioassay and in situ seed-set examination. The availability of DHs provided the opportunity of working with genetically homogenous pollen and female parents. The aniline blue fluorescence (ABF) method was applied to detect callose accumulation in pollen and pistil. Clear cross-compatibility/incompatibility situations were observed and confirmed by in situ seed-set analysis. Cross-compatibility analysis of hybrid combinations involving different DHs corroborated the crossing behaviour observed at the DH level. Expression of the self-incompatibility system did not appear to be affected by the low vigour of the DH. The crossing-behaviour distribution observed within DHs derived from clone IF200 confirmed that self-incompatibility in C. canephora is a gametophytic self-incompatibility system controlled by a single locus (S-locus). Reduced seed-set developments following incompatible crosses may indicate the occurrence of pseudo-incompatibility. Molecular marker linkage analysis showed that the S-locus is associated with an RFLP marker on linkage group 9. The availability of a linked DNA marker should facilitate the genetic analysis of self-incompatibility in relation to coffee breeding programmes.     

Distyly and pollen dimorphism inLinum suffruticosum (Linaceae)

The Mediterranean distylousLinum suffruticosum has dimorphic pollen. That from short-styled plants has sub-monomorphic surface excrescences with minute papillae; that from long-styled plants has strongly dimorphic excrescences with conspicuous papillae. The differences are much like those described in species of other sections of the genus. Pollen of the related homostylousL. tenuifolium has monomorphic pollen. It combines characteristics of bothL. suffruticosum types but resembles that of the long-styled plants somewhat more closely. Ribbonlike styles of long-styled plants ofL. suffruticosum provide another feature which seems to be controlled by the S supergene thought to be associated with distylic incompatibility. The pollen ofL. suffruticosum andL. tenuifolium is very similar to that of some species of sectionLinastrum and would support their placement in that section.     

Dimorphisms and self-incompatibility in the distylous species <Emphasis Type="Italic">Palicourea demissa</Emphasis> (Rubiaceae): possible implications for its reproductive output

Distyly has been interpreted as a mechanism that favors cross-fertilization. In this research we describe floral attributes and ancillary floral polymorphisms typically associated to heterostylous plants in Palicourea demissa (Rubiaceae), a distylous shrub of the Venezuelan Andes cloud forests. A hand-pollination experiment was done to evaluate self- and intramorph incompatibility and female reproductive output in both floral morphs. The studied population was morphologically distylous but morph differences in most ancillary floral polymorphisms and reciprocity of the sexual organ heights were found. The floral morphs were self-incompatible and did not differ in fruit set under controlled cross-pollination conditions, but at the population level they exhibited imperfect reciprocal herkogamy. Fruits and seeds of short-styled plants were larger than those of long-styled plants and fruit set was higher in short-styled plants under natural conditions, suggesting a higher reproductive potential among short-styled plants. Given the 1:1 morph ratio within the studied population, further evidence is needed to determine the influence of floral visitors and seed dispersers in the expression of heterostyly in P. demissa under natural conditions.     

An unusual homostyle inHedyotis caerulea (Rubiaceae)

Hedyotis caerulea, a spring flowering herb widely distributed in eastern North America, has distylous flowers that differ by a number of morphological and physiological traits. The presence of a strong incompatibility system is indicated by the fact that intramorph crosses or self-pollinations produced little or no seed and intermorph crosses produced copious seed. An unusual homostyle was located that had most floral characters intermediate between pin and thrum flowers, although its pollen size was that of pin. The homostyle was only moderately self-compatible, and its pollen did not behave as pin pollen on thrum stigmas. It appears that, despite their intermediate position and morphology, the homostyle stigmas were fundamentally pin. Although the exceptional rarity of the homostyle suggests that it is an inadaptive failure, workers should watch for its further occurrence since additional study of it may provide insights into the genetic and physiological basis of heterostyly in theRubiaceae.     

Organization and mapping of legumin genes in Pisum

Summary The organization of three classes of legumin gene has been studied by exploiting restriction fragment length polymorphisms. Hybridization of cDNA probes, representing different sub-families of legumin gene, to DNA from F₂ and F₆ plants from selected crosses showed that there was a tight linkage of individual genes within each of two sub-families. One of these sub-families has been mapped to a locus on chromosome 7 close to r, while the other maps to a locus near a on chromosome 1. The results from one of the crosses analyzed indicated that a third class of legumin gene is also linked to a.     

Breeding system variation, genetics and evolution in the Turneraceae

We review the genetics and evolution of breeding systems in the Turneraceae. Distyly occurs in seven of 10 genera and 81% of species. The remaining species are homostylous. Polyploid evolution has been significant in Turnera. Approximately 60% of species are polyploid ranging from diploid through decaploid. No relationship between breeding system and polyploidy is evident. The genetics of distyly involves a one-locus two-allele system (S and s). Evidence from crosses with homostylous species and mutants is consistent with the possibility that a "Primula-type" supergene underlies distyly but does not prove this to be the case. A polygalacturonase, and an alpha-dioxygenase specific to the transmitting tissue of short-styled plants both exhibit morph-limited expression in concert with predictions from an evolutionary model. The function of the proteins in distyly, if any, is unknown. We have begun constructing a fine-scale genetic map of Turnera. Two genetic markers lie within 0.2 cm of the distyly locus. This should provide a starting point for positional cloning of the distyly locus and reveal the genetic architecture and molecular basis of distyly.