POLLEN COMPETITION AND RELATEDNESS IN HAPLOPAPPUS SECTION ISOPAPPUS (COMPOSITAE). II.

Pollen competition in mixed pollinations involving a time handicap was studied among the five aneuploid members of section Isopappus of Haplopappus. Foreign pollen was applied to the stigmas of a plant followed after a delay of 0–180 min by domestic pollen. Domestic pollen was prepotent over foreign pollen in all cases, but with increasing delay an increasing percentage of hybrids appeared in the progeny. The time interval required to produce 50% of hybrids in the progeny (at which time the two pollen types were competitively matched in potency) was determined for each cross. The interval is correlated with relatedness, with chromosome number, and with length of the style of the pollen parent. It can be used as an estimate of the potential frequency of hybridization in nature, with all other factors being equal.     

CHROMOSOME PAIRING AND POLLEN FERTILITY IN INTERSPECIFIC HYBRIDS OF SPECIES OF PARTHENIUM (ASTERACEAE)

Meiotic analyses and pollen viability tests were performed on F, hybrids between diploid guayule (Parthenium argentatum Gray 2n = 36), P. rollinsianum Rzedowski (2n = 36), P. alpinum var. tetraneuris Barneby (2n = 36), and P. alpinum var. alpinum Nutt. (2n = 36). Parthenium chromosomes are small and karyomorphologically similar, and meiotic analysis is difficult because of chromosome clumping. However, cytogenetic studies at metaphase I indicated univalents can be seen in a lateral view of the metaphase plate. Chromosome pairing and the number of univalents varied within and between the interspecific hybrids, with an average univalent number of 1.54 for the P. rollinsianum hybrids, 2.36 for the P. alpinum var. tetraneuris hybrids, and 2.46 for the P. alpinum var. alpinum hybrids. Pollen viability tests for the parental species and the hybrids were conducted by germination of pollen grains on stigmas. The percent of viable pollen recorded for the diploid guayule hybrids with P. rollinsianum, P. alpinum var. tetraneuris, and P. alpinum var. alpinum are 21.94, 13.47, and 11.17, respectively. The degree of chromosome pairing and pollen viability is striking because there are many morphological differences between the parents. The chromosome homology of these species based on their pairing behavior allows for the design of a backcross breeding program that would permit the transfer of the desirable characteristics from these species into diploid guayule.     

Somatic hybrids between Solanum etuberosum and diploid,tuber bearing Solanum clones

Electrofusion was used to obtain somatic hybrids between Solanum etuberosum (2n=2x=24) and two diploid potato lines. These hybridizations were conducted to determine if haploidxwild species hybrids are better fusion partners than conventional S. tuberosumGp. Tuberosum haploids. Restriction fragment length polymerase (RFLP) analyses of the putative somatic hybrids confirmed that each parental genome was present. The somatic hybrids between S. etuberosum and a haploid S. tuberosum clone, US-W730, were stunted and had curled, purple leaves. In contrast, somatic hybrids between S. etuberosum and a haploidxwild species hybrid (US-W 730 haploidx S. berthaultii), were vigorous and generally tuberized under field conditions. These hybrids were designated as E+BT somatic hybrids. Analyses of 23 E+BT somatic hybrids revealed a statistically significant bias towards the retention of S. etuberosum chloroplasts. Stylar incompatibilities were observed when the E+BT somatic hybrids were used as pollen donors in crosses with S. tuberosum cultivars. Reciprocal crosses did not show this incompatibility. The progeny were vigorous and had improved tuber traits when compared to the maternal E+BT parent. RFLP analyses of three sexual progeny lines confirmed the presence of all 12 S. etuberosum chromosomes. In two of these lines, RFLPs that marked each of the 24 chromosome arms of S. etuberosum were present. However, RFLP markers specific for regions on chromosomes 2, 7, and 11 were missing from the third clone. Because other markers for these chromosomes were present in the progeny line, these results indicated the likelihood of pairing and recombination between S. etuberosum and S. tuberosum chromosomes.     

RELATIONSHIP OF WOODY PARTHENIUM ARGENTATUM AND HERBACEOUS P. HISPIDUM VAR. AURICULATUM (ASTERACEAE)

Interspecific hybrids between woody Parthenium argentatum Gray (guayule), native to Mexico and Southwest Texas, and herbaceous perennial P. hispidum var. auriculatum (Britton) Rollins, native to the United States, were obtained successfully. The F₁ hybrids were intermediate for most morphological characters with the exception of the short woody stem, yellow pollen color, and the trichome morphology. Chromosome counts revealed the presence of 2n = 36 A-chromosomes in P. argentatum. The same number of A-chromosomes and four B-chromosomes were found in P. hispidum var. auriculatum. Observations of pollen mother cells showed regular meiosis in both parental species. At diakinesis, chiasmata averaged 1.12 and 1.24 per bivalent for P. argentatum and P. hispidum var. auriculatum, respectively. Meiotic behavior of the F₁ hybrids was irregular. F₁ hybrids averaged 4.43 univalents at metaphase I, 1.95 laggards at anaphase I, and 1.62 micronuclei at the tetrad stage. The low pollen stainability (5.1%) in the F₁ hybrids and the limited number of viable BC₁ seeds (4.07%) may be reflections of the irregular meiosis. Although these primary hybrids are partially fertile, they can be used to introduce desirable characteristics of P. hispidum var. auriculatum, such as herbaceous perennial habit, regrowth ability, and cold tolerance into guayule.     

STERILITY BARRIERS OF SOME ARTIFICIAL F1 ORCHID HYBRIDS: MALE STERILITY. I. MICROSPOROGENESIS AND POLLEN GERMINATION

Microsporogenesis, pollen germination and fertility of males gametes were studied in 24 artificial intergeneric and interspecific F₁ hybrids of orchids. Although parental species had the same chromosome number (2n = 40), microsporogenesis of the hybrids was irregular due to the lack of homology of the chromosomes of the parental species. This led to formation of tetrads of microspores without micronuclei, tetrads with 1–8 micronuclei, triads, dyads with and without micronuclei, and monads. Chromosomes numbers found in haploid microsporocytes ranged from 7 to 40; in micronuclei the chromosome number varied between 1 and 5. In terms of pollen germination, three situations were observed: 1) hybrids whose pollen grains did not germinate in the stigma; 2) hybrids in which the pollen tubes grew down in the style, but did not penetrate into the ovary; 3) hybrids in which the pollen tubes grew down normally through the ovary, reaching the ovules. When the pollen tubes did not penetrate the ovary no fruit was formed. Therefore germination tests carried out in vitro may not indicate pollen fertility, because pollen tube growth in the style of the flower may be insufficient to induce fruit formation or to accomplish fertilization.     

The evolutionary history of Drosophila buzzatii

Introgression of a chromosome segment from Drosophila serido into the genome of its sibling D. buzzatii brought about the release of mutator potential in the hybrids. Mutator activity was determined by examining the frequency of new chromosomal rearrangements, that appeared only in the progeny of hybrid individuals. Mutation frequency was 30 times greater in the progeny of hybrid males than in that of hybrid females. There was a remarkable influence of the D. buzzatii genetic background on the frequency of production of these new rearrangements. The appearance of a new rearrangement did not depend on the genotype of the larva that bore it, but only on that of its hybrid progenitor. Among the new rearrangements there were inversions, translocations, and duplications. The number of translocations was significantly lower than that of inversions or duplications; this last type was the most frequently recorded. The distribution of the aberrations among the four major autosomes seemed to be homogeneous, although the total number of breakpoints was significantly greater in chromosome 4 than in the others. No rearrangement was found on the X chromosome. Breakpoints within three of the four affected autosomes were not randomly distributed.     

Interspecific Hybridization of Pennisetum glaucum (L) R. Br. with Wild Relatives

To widen the germplasm base for the introgression of economically important traits such as resistance to biotic and abiotic stresses from related species, crosses of cultivated pearl millet were made with pollen from four related species differing in the basic chromosome number (x=5,7,8 and 9). Embryo rescue technique was used to obtain viable progeny. Pollinations of pearl millet with Pennisetum ramosum (2n=2x=10) did not give any viable progeny. Pearl millet interspecific hybrids with P. schwelnfurthii (2n-2x-14), P. mezianum (2n=4x-32) and P. orientale (2n=2x=18) were obtained. The hybrid between P. glaucum and P. mezianum (2n=23) is the first successful report. Interspecific hybrid plants resembled their corresponding pollen parents. Southern blots of Psfl digested DNAs from interspecific hybrids and the parental species were hybridized to a full length rDNA to further confirm their hybridity. This further revealed differential amplification of two rDNA repeats among the F₁ hybrids from the same cross (P. glaucum X P. orientale).     

Interspecific hybridization between Vigna radiata (L.) Wilczek and V. glabrescens

Summary Interspecific hybrids of the mungbean, Vigna radiata (L.) Wilczek (2n=22) and V. glabrescens (2n=44) were generated with the aid of embryo culture. V. glabrescens x V. radiata hybrids were recovered via germination of the immature embryos. Reciprocal hybrids were obtained via shoot formation from embryonic callus. The authenticity of the hybrids was determined by morphological characteristics, chromosome number, and isozyme patterns. The hybrids were highly sterile upon selfing, but backcrossing to the diploid parent yielded viable seeds. Some of the plants resembled the diploid parent morphologically while others resembled neither parent. The backcross plants were sufficiently fertile to give a large number of mature, selfed seeds. Plants obtained differed morphologically and in their isozyme patterns from either parent, indicating introgression. These progeny populations will be used as bridging materials to transfer pest resistance from the wild tetraploid to the cultivated mungbean.     

CYTOGENETIC STUDIES OF CARTHAMUS DIVARICATUS WITH ELEVEN PAIRS OF CHROMOSOMES AND ITS RELATIONSHIP TO OTHER CARTHAMUS SPECIES (COMPOSITAE)

Carthamus divaricatus (Beg. et Vacc.) Pamp., found only in Libya, has 11 pairs of chromosomes, a new chromosome number in the genus. The species is distinct morphologically. It has yellow, purple, and white corollas, yellow pollen, dark-purple striped anthers, horizontal branches, and strongly divaricate outer involucral bracts. The terminal portion of the middle involucral bracts is dentate and reddish brown. It is self-incompatible. Meiosis is regular in the different corolla-color types of C. divaricatus and their intraspecific hybrids. C. divaricatus was crossed to six species with n = 12, to three species with n = 10, to C. lanatus with n = 22, and to two species with n = 32 chromosomes. The morphological characteristics and cross-ability of the parental species plus the pollen viability, seed-set, and meiotic behavior of the hybrids involving C. divaricatus and other Carthamus species indicated that C. divaricatus is very closely related to species with n = 10, closely related to C. lanatus with n = 22, and less closely related to C. tinctorius with n = 12 chromosomes. C. divaricatus seems to be distantly related to C. nitidus (n = 12). It is proposed that C. divaricatus be included provisionally with 10-chromosome species in Section II. Alternative hypotheses for the development of the three basic chromosome numbers are discussed.     

The importance of pre-mating barriers and the local demographic context for contemporary mating patterns in hybrid zones of Eucalyptus aggregata and Eucalyptus rubida

The frequency of hybridization in plants is context dependent and can be influenced by the local mating environment. We used progeny arrays and admixture and pollen dispersal analyses to assess the relative importance of pre‐mating reproductive barriers and the local demographic environment as explanations of variation in hybrid frequency in three mapped hybrid zones of Eucalyptus aggregata and E. rubida. A total of 731 open‐pollinated progeny from 36 E. aggregata maternal parents were genotyped using six microsatellite markers. Admixture analysis identified substantial variation in hybrid frequency among progeny arrays (0–76.9%). In one hybrid zone, hybrid frequency was related to pre‐mating barriers (degree of flowering synchrony) and demographic components of the local mating environment (decreasing population size, closer proximity to E. rubida and hybrid trees). At this site, average pollen dispersal distance was less and almost half (46%) of the hybrid progeny were sired by local E. rubida and hybrid trees. In contrast, at the other two sites, pre‐mating and demographic factors were not related to hybrid frequency. Compared to the first hybrid zone where most of the E. rubida (76%) and all hybrids flowered, in the remaining sites fewer E. rubida (22–41%) and hybrid trees (0–50%) flowered and their reproductive success was lower (sired 0–23% of hybrids). As a result, most hybrids were sired by external E. rubida/hybrids located at least 2–3 km away. These results indicate that although pre‐mating barriers and local demography can influence patterns of hybridization, their importance can depend upon the scale of pollen dispersal.     

Introgressive hybridization between a native and an introduced species:Viola lutea subsp.Sudetica versusV. Tricolor

A hybrid swarm betweenViola lutea subsp.sudetica (2n=50, native species) andViola tricolor (2n=26, introduced species) originated in the 1970’s in the Krkono?e Mts. Analyses of chromosome numbers, reproductive biology, morphology, and ecology gave the following results: (1) Compared to the plants found in the 1970’s, the number of colour morphs have decreased and the types now prevailing in the field are morphologically closer toV. lutea subsp.sudetica, forming a continuum. (2) In the field, hybrids having approximately the same chromosome number as the primary hybrids are most common. Some plants of the hybrid swarm have certain characters unknown to their parents. (3) In the field, autogamous types similar toV. tricolor were found. (4) A limited number of plants from the field and culture have higher somatic chromosome numbers thanV. lutea subsp.sudetica; there was a tendency towards increasing chromosome numbers in their progeny (up to 2n=62). These plants have some new morphological characters (a small proportion of hexacolpate pollen) not found in the parents (nor in the other hybrids with prevailing tetracolpate and pentacolpate pollen grains) and higher pollen fertility in comparison to the other hybrids. These plants also have the highest germination rate. (5) There is a tendency for chromosome numbers to decline in the progeny of open pollinated hybrid plants in the lowland experimental graden. (6) The phenology of the plants in the mountain grasslands and the lowland garden is different; the parents behave in a totally contrasting manner. (7) In the field at least some hybrids extend outside the geographical and ecological ranges of the parental species, invading new communities. (8) Seeds ofV. tricolor do not show any dormancy and germinate in the year of production; most of theV. lutea subsp.sudetica seeds germinate during the spring of the following year. Hybrids with intermediate chromosome numbers had both types of germination strategy. The germination rate of intermediates with high chromosome numbers was even higher than that ofV. tricolor.     

Cytogenetic analysis of reciprocal hybrids and their parents between <Emphasis Type="Italic">Larix leptolepis</Emphasis> and <Emphasis Type="Italic">Larix gmelinii</Emphasis>: implications for identifying hybrids

We studied the parental taxa and the interspecific reciprocal hybrids between Larix leptolepis with Larix gmelinii, using classical cytogenetic methods, as well as fluorescence in situ hybridization (FISH) and genomic in situ hybridization. A high frequency (>90%) of complete bivalent formation was observed in reciprocal hybrids. Less than 10% of pollen mother cells exhibited abnormalities. The most frequent abnormalities were bridges. Multivalent chromosome associations were also observed in both reciprocal hybrids, suggesting that some chromosome interchange events did occur, and introgressions from one to the other species were possible. Intergenomic recombination indicates that genes might be readily introgressed into one species from the other in the genus Larix. Interspecific hybridization may be a potential method for genetic improvement in larch. FISH markers documented that the recombinant genomes of reciprocal hybrids were strictly additive and stable, indicating that FISH also might be a useful tool in Larix breeding.     

Isolation and characterization of potato-tomato somatic hybrids using an amylose-free potato mutant as parental genotype

Summary Using different genotypes of tomato and diploid potato, possessing alien selectable markers as well as endogenous markers, very high frequencies of protoplast fusion hybrids were obtained. One endogenous genetic marker, the amylose-free (amf) mutant of potato, was helpful not only for the confirmation of fusion products but also for the study of genetic complementation and the segregation of amylose-free starch in microspores. Cytological analysis of the fusion hybrids indicated that except for one which was hexaploid, all of them had a perfectly balanced chromosome number of allotetraploid constitution (2n = 4x = 48). Despite normal chromosome pairing and a diploid behaviour, the microspores in some of the fusion hybrids segregated for the recessive amf-locus. This anomalous segregation of a recessive character in these hybrids was shown not to be due to chromosome elimination or to the absence of the wild-type tomato Amf gene. Although all fusion hybrids were totally sterile, the hexaploid produced stainable pollen and berries with badly developed seeds. Embryo rescue has so far failed to produce backcross progeny.     

A CYTOGENETIC ANALYSIS OF CERTAIN POLYPLOIDS IN GRINDELIA (COMPOSITAE)

Two diploid taxa, Grindelia procera and G. camporum, and 3 tetraploid ones, G. camporum, G. hirsutula, and G. stricta, have been studied to ascertain their interrelationships. Meiosis in diploid parental strains was regular, the common chromosome configuration being 5 rod bivalents and 1 ring bivalent. The average chiasmata frequency per chromosome was 0.60. Pollen fertility was about 90% in all strains examined. Diploid interspecific hybrids had normal meiosis with an average chiasmata frequency of 0.56 per chromosome. No heterozygosity for inversions or interchanges was detected, and pollen fertility was above 85%. Meiosis in parental tetraploid strains was characterized by the presence of quadrivalents in addition to a complementary number of bivalents. The average chiasmata frequency per chromosome was 0.59 and pollen fertility was generally about 80%. Tetraploid interspecific hybrids also had quadrivalents, normal meiosis, and high pollen fertility. Close genetic relationships between the diploids and between the tetraploids are indicated, and geographical, ecological, and seasonal barriers to gene exchange exist. Attempts to obtain hybrids between diploids and tetraploids were successful in a few cases. The hybrids were tetraploid and had normal meiosis and fertility similar to parental and F₁ tetraploids. Their origin was by the union of unreduced gametes of the diploid female parent and normal pollen from the tetraploid parent. On the basis of chromosome homology, normal meiosis, plus high fertility exhibited in the diploid, tetraploid, and diploid X tetraploid interspecific hybrids, these species of Grindelia are considered to be a part of an autopolyploid complex. Gene exchange between diploids and diploids, tetraploids and tetraploids, and diploids and tetraploids is possible. Tetraploid G. camporum may have originated by hybridization between G. procera and diploid G. camporum with subsequent doubling of chromosomes and selection for the combined characteristics of the diploids.     

Pairing and recombination at meiosis of Brassica rapa (AA) × Brassica napus (AACC) hybrids

Interspecific crosses contribute significantly to plant evolution enabling gene exchanges between species. The efficiency of interspecific crosses depends on the similarity between the implicated genomes as high levels of genome similarity are required to ensure appropriate chromosome pairing and genetic recombination. Brassica napus (AACC) is an allopolyploid, resulting from natural hybridization between Brassica rapa (AA) and Brassica oleracea (CC), both being diploid species derived from a common ancestor. To study the relationships between genomes of these Brassica species, we have determined simultaneously the pairing and recombination pattern of A and C chromosomes during meiosis of AAC triploid hybrids, which result from the interspecific cross between natural B. napus and B. rapa. Different AAC triploid hybrids and their progenies have been analysed using cytogenetic, BAC-FISH, and molecular techniques. In 71% of the pollen mother cells, homologous A chromosomes paired regularly, and usually one chromosome of each pair was transmitted to the progeny. C chromosomes remained mainly univalent, but were involved in homoeologous pairing in 21.5% of the cells, and 13% of the transmitted C chromosomes were either recombined or broken. The rate of transmission of C chromosomes depended on the identity of the particular chromosome and on the way the hybrid was crossed, as the male or as the female parent, to B. napus or to B. rapa. Gene transfers in triploid hybrids are favoured between A genomes of B. rapa and B. napus, but also occur between A and C genomes though at lower rates.     

Gametes with somatic chromosome number and their significance in interspecific hybridization in Fuchsia

Sexual polyploidization has both a theoretical as well as an applied significance. Morphological screening for large pollen grains and shape of pollen produced by the individual, cytological investigation of hybrid progeny, and unbalanced separation of chromosomes at anaphase I in pollen mother cells were used to detect the gametes with somatic chromosome number in Fuchsia. The interspecific hybrids of F. fulgens (sect. Ellobium) × F. magellanica (sect. Quelusia), F. fulgens (sect. Ellobium) × F. splendens (sect. Ellobium), and F. triphylla (sect. Fuchsia) × F. splendens (sect. Ellobium) produced at the University of Auckland, New Zealand, showed both large and normal pollen grains in the same anther indicating the presence of unreduced gametes. Cytological investigation carried out on the hybrid progeny of F. fulgens (diploid, 2n=22, sect. Ellobium) × F. magellanica (tetraploid, 2n=44, sect. Quelusia) and F. triphylla (diploid, sect. Fuchsia) × F. arborescens (diploid, sect. Schufia) revealed unexpected chromosome numbers of 2n=44 and 2n=33, respectively. In general, the hybrids showed low fertility caused by genetically unbalanced gametes resulted from random disjunction of chromosomes at anaphase I. Studies on meiosis together with the presence of different shapes and sizes of pollen grains in Fuchsia proved indirectly that unreduced gametes are the products of first division meiotic nuclear restitution. These unreduced gametes were viable irrespective of pollen shape, their predominance in the hybrids, nuclear DNA amount and species phylogenetic position.     

Characterisation of progeny from backcrosses of triploid hybrids between Hordeum vulgare L. (2x) and H. bulbosum L (4x) to H. vulgare

Interspecific hybridisations between Hordeum vulgare L. (cultivated barley) and H. bulbosum L. (bulbous barley grass) have been carried out to transfer desirable traits, such as disease resistance, from the wild species into barley. In this paper we report the results of an extensive backcrossing programme of triploid hybrids (H. vulgare 2x x H. bulbosum 4x) to two cultivars of H. vulgare. Progenies were characterised cytologically and by restriction fragment length polymorphism analysis and comprised (1) haploid and diploid H. vulgare plants, (2) hybrids and aneuploids, (3) single and double monosomic substitutions of H. bulbosum chromosomes into H. vulgare and (4) chromosomal rearrangements and recombinants. Five out of the seven possible single monosomic chromosome substitutions have now been identified amongst backcross progeny and will be valuable for directed gene introgression and genome homoeology studies. The presence amongst progeny of 1 plant with an H. vulgare-H. bulbosum translocated chromosome and one recombinant indicates the value of fertile triploid hybrids for interspecific gene introgression.     

Response of wheatgrasses and wheat × wheatgrass hybrids to barley yellow dwarf virus

Summary Resistance to barley yellow dwarf virus (BYDV), manifested by low enzyme-linked immunosorbent assay (ELISA) values in plants exposed to viruliferous aphids, was identified in several wheatgrasses (Agropyron spp.). ELISA results were similar for root and leaf extracts of infested plants. No difference in reaction to BYDV was found between plants grown in the field and those in the growth chamber. Interspecific hybrids were generated using pollen from single resistant plants of Agropyron spp. to pollinate soft red winter wheat spikes. Resistance in hybrids appeared to be at the level of virus replication rather than at the level of vector inoculation. The hybrids varied in their reaction to BYDV. Expression of BYDV resistance in hybrids was influenced not only by wheat genotype and Agropyron species but, in some cases, reaction varied even among hybrids between the same wheat genotype and Agropyron plant. Implications of these results are discussed.Contribution from the Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907, and USDA-ARS. The research was supported in part by Public Varieties of Indiana. Purdue Univ. Agric. Exp. Stn. Journal No. 11656     

UNUSUAL CYTOLOGICAL PATTERNS IN MICROSPOROGENESIS AND POLLEN DEVELOPMENT OF EVOLUTIONARY SIGNIFICANCE IN THE MIMULUS GLABRATUS COMPLEX (SCROPHULARIACEAE)

Four populations of Mimulus glabratus var. utahensis Pennell from the Great Basin and seven of M. glabratus var. fremontii (Bentham) Grant from the New Mexico–Texas–northeastern Mexico area were intercrossed and their F₁ hybrids grown. Cytology and fertility of both the parental populations and the F₁ hybrids were studied. The following cytological abnormalities were observed in microsporogenesis: cytomixis, the stretching of one or more chromosomes from cell to cell; multipolar divisions, separation of the chromosome complement into two or more parts; unequal disjunction; spontaneous polyploidization; and the production of encapsulated pollen tetrads. Typically, these abnormalities were rare or not observed in the parents, were rare in the intravarietal hybrids, but were more common in the intervarietal hybrids. They were closely associated with, in fact were the probably causes of, barriers to gene exchange between these two diploid (n = 15) varieties. Thus, the apparent causes of barriers to gene exchange in intervarietal hybrids are the likely mechanisms for the evolution of aneuploidy and polyploidy so characteristic of the rest of the Mimulus glabratus complex.     

RELATIVE FITNESS OF SELFED AND OUTCROSSED PROGENY IN A SELF-COMPATIBLE,PROTANDROUS SPECIES,SABATIA ANGULARIS L. (GENTIANACEAE): A COMPARISON IN THREE ENVIRONMENTS

The consequences of selfing were examined for a population of self-compatible, protandrous, Sabatia angularis L. (Gentianaceae). Field-collected plants were hand-pollinated in the greenhouse to produce selfed progeny and outcrossed progeny from parents separated by a maximum of 5 m (near-outcross) and 85 m (far-outcross) in the field. Self, near-outcross, and far-outcross half sib progeny were grown in the greenhouse, a garden plot, and their native habitat. Progeny were compared by multiplicative fitness functions based on seed production per hand-pollination, seed germination, rosette formation, survival to reproduction, and reproduction in each environment. Variation in reproduction among progeny groups was influenced by the environment in which they were grown. Significant inbreeding depression was detected between the self and far-outcross progeny in each environment. Only the natural environment demonstrated a greater than 50% reduction in relative fitness of self compared to near-outcross progeny. This is of biological relevance since near-outcross hand-pollinations occurred within the range of pollen and seed dispersal suggesting that inbreeding depression in S. angularis is strong enough to maintain outcrossing in the study population. In the field, the far-outcross progeny outperformed the near-outcross progeny suggesting local population substructure. The magnitude of the inbreeding depression expressed among the self progeny was the greatest in the field, intermediate in the garden plot, and the least in the greenhouse.