Interspecific Pollination Research Articles

Stigma Morphology and Pollination in Arachis L. (Leguminosae)

Our study was undertaken to determine whether wild species of Arachis have the same type of stigma as A. hypogaea, to find out whether stigma characteristics explain the limited seed set in the perennial species and to devise ways of increasing the efficiency of interspecific pollinations particularly with the perennials as females parents

Incompatibility in Dendrobium (Orchidaceae)

A unique self-incompatibility system in Dendrobium is demonstrated by more than 1700 pollination experiments. The majority (72%) of the 61 species that were self-pollinated showed self-sterility. In contrast with many other orchid genera Dendrobium showed high incompatibility in interspecific pollinations. Self-and interspecific incompatibility is expressed by flower abscission and not by inhibition of pollen germination or pollen tube growth. The incompatibility system is gametophytic and complementary, and it is likely that the auxin content in the pollinia triggers the incompatibility reaction. Microscopical investigations on the detached cells of the stigma (here called eleutherocytes) after compatible and incompatible pollinations, suggest that the incompatibility response is probably controlled by these cells.

Relationships of pollen size, pistil length and pollen tube growth rates in Rhododendron and their influence on hybridization

Pollen size and pistil length data have been collected for 93 species of Rhododendron (Ericaceae) belonging to a number of different subgeneric taxa. For a sample of eight species in section Vireya, pollen tube growth in the style after selfor interspecific pollination has been quantified. Pollen volume and the time taken for pollen tubes to reach the ovary were both related to pistil length. Pollen-tube growth rates were generally greater for species with longer pistils and larger pollen. Increasing temperature increased the rate of pollen-tube growth. There was no detectable effect of pollen tube density on tube growth rate in the style. After interspecific pollinations tube growth rates in foreign styles could be faster or slower than in self styles. A semisterile individual with two viable pollen grains per tetrad and a plant grafted as scion to a longer-styled stock both showed more rapid pollen-tube growth than expected on the basis of pistil size. Data collected for 26 species in section Vireya showed that where extreme disparity of pollen/pistil size causes failure of interspecific crosses, one or more bridging species with intermediate pollen/pistil size can generally be selected.

Aspects of Hybridization between the Closely Related Senecio vulgaris L. and Senecio vernalis Waldst. & Kit.

The results from an investigation of hybridization between closely related Senecio vulgaris (2n = 40) and S. vernalis (2n = 20) are reported. In the two mixed populations examined the frequency of the triploid (2n=30) S. × helwingii was found to be 1.1 and 1.5% respectively. The spatial distribution of hybrid frequency at least in one of the populations examined seems to be roughly correlated with abundance of parent taxa. Hybridization between the two species under experimental conditions is easy. In nature the predominant self-fertilization of S. vulgaris and the rarity of interspecific pollinator flights as observed in a garden trial might be the major factors limiting hybrid formation. Experimental hybridization between F1 hybrids, their backcross to both parent species and self-pollination of the F1 hybrid did not result in hybrid progeny. However, plants could be raised from spontaneously formed achenes on the F1. These were either tetraploid (2n=40) or +/- hexaploid (2n=57-61). It seems likely that these were formed by pollination of the F1 hybrid with pollen from S. vulgaris in the case of the tetraploid and by polyploidization of the F1 hybrid in the hexaploids. In both these pollen and seed fertility recovered remarkably in comparison to the Fl. These processes involving S. vulgaris and S. vernalis are compared to those known from S. vulgaris and S. squalidus in the British Isles.

Interspecific Hybridization of Papaya with Other Carica Species

Abstract Interspecific hybridizations were attempted between papaya (Carica papaya L.) and six Carica taxa, including C. monoica Desf., C. parviflora (A. DC.) Solms, C. pubescens Lenne et Koch, C. quercifolia (St. Hil.) Hieron., stipulata Badillo, and C. × heilbornii Badillo nm. pentagona (Heilborn). Prezygotic barriers were minimal; pollen tubes of wild species freely penetrated into the seed cavity of papaya, and papaya pollen tubes were similarly unhindered in reciprocal pollinations on C. pubescens. Postzygotic barriers were formidable due to ovule abortion and endosperm failure. However, dissection of more than 150 C. papaya fruits 90 to 180 days after interspecific pollination yielded at least a few hybrid embryos of each species combination. All crosses in which C. papaya was the male parent failed, with the exception of C. pubescens × C. papaya, which succeeded only after young ovules were cultured 30 to 45 days after pollination. Multiple embryos were common in all successful crosses, and these were shown to be of zygotic origin by analyses of isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase isozymes in parental and hybrid tissues. Hybrids successfully recovered from in vitro cultures included C. papaya × C. pubescens and reciprocal, C. papaya × C. quercifolia, and C. papaya × C. stipulata.

Pollen-pistil interactions inGrevillea banksii

Abstract Morphology and ultrastructure of stigma, transmitting tissue and pollen were examined in Grevillea banksii R. Br. (Proteaceae), a bird-pollinated shrub with stylar presentation of pollen. Stigmatic cells are not cuticularised and secrete copious lipidic exudate. Intercellular material of the thick primary walls of transmitting tissue cells stains positively for protein. The pollen exine is cavate and foveolate, but labile protein could be detected only in the thickened intine below germ pores. Self and non-self pollen of G. banksii, germinated on the stigma, both show normal protein mobilisation and synthesis of wall material. Ectexine of germinated grains consistently appears saccate. Intra- and interspecific pollinations using five other species of Grevillea and one of Persoonia as ‘foreign’ pollen sources, showed no pollen rejection at the stigma or in the upper transmitting tissue. Sporophytic control in compatibility regulation, believed most usual with stylar presentation, is inferred to be...

Temporal and spatial patterns in the production of pollen, ovules and seeds in pseudogamous blackberries (Rubus subgenus Rubus)

Significant variation in the number of stamens and ovules per flower, the stamen/ovule ratio, and the number of seeds per berry was found among seven blackberry species, each represented by one clone, and to a much lesser extent among inflorescences within species. Inflorescence size and architecture were found to have no major influence on these reproductive parameters.The position of a flower within the inflorescence strongly influences its onset of anthesis, which in turn is closely correlated with these reproductive parameters. Ovule number decreases with time, although in some species it increases again at the end of the flowering season. Number of seeds decreases more or less linearly with time, although there is an unexpectedly high number of the earliest berries of the triploid species, which is probably the result of interspecific pollination. Pollen production estimated in one species decreases with time, per theca, per flower and per ovule, whereas the percentage of good pollen grains remains unaltered.

An SEM Study of Pollen Tube Growth in Intra- and Interspecific Crosses between Lilium Species

As a part of our study on interspecific cross barriers in Lilium spp., we compared pollen tube growth in intraspecific (L. longiflorum) and interspecific (L. longiflorum x Lilium x `Mont Blanc') crosses, using scanning electron microscopy. After penetration into the stigma, pollen tubes in the intraspecific pollination grow straight along the longitudinal axis of the style. In the ovary they follow the papillate area between two rows of ovules, after which they turn and grow between two bordering ovules to penetrate the micropyles. In contrast, pollen tubes in the interspecific pollination show a winding growth pattern, terminating in the upper half of the style, which means an interspecific cross barrier. After pollination by the cut-style method directly on top of the ovary, interspecific pollen tubes enter the ovary, form sperm cells, grow straight along the papillate tissue between the ovules, and turn toward the micropyles, as in the intraspecific pollination. Some of them penetrate a micropyle; most of them stop in front of the micropyles, indicating that different stimuli lead the pollen tubes toward and into the micropyle, respectively. The number of micropyles in which a pollen tube can be observed is higher than the number of seeds obtained in previous breeding programs with the cut-style method. Thus, after cut-style pollination a cross barrier is found inside or just in front of the ovules. However, the low number of seeds obtained after intraspecific cut-style pollination makes it uncertain whether this barrier is caused by interspecifity or by the pollination method itself.

Breeding systems and pollen tube behaviour in compatible and incompatible crosses in New Zealand species ofRanunculusL.

Abstract Breeding systems were investigated in 13 New Zealand species of Ranunculus; all were found to be self-compatible. In self-, cross-, and interspecific pollinations there is a very clear reduction of pollen tube number to one in the style. This suggests pollen tube competition or selection of pollen tubes by the stylar tissue but no morphological reason for this could be ascertained. The repeated observation of germination of single pollen grains on the stigma suggests that there is no population effect enhancing pollen germination in these species of Ranunculus.

Effect of three pollination methods on embryo development and seedset in intra- and interspecific crosses between seven Lilium species

Interspecific crosses were made between seven Lilium species, viz. L. candidum, L. concolor, L. dauricum, L. henryi, L. longiflorum, L. nepalense and L. rubellum. A complete diallel cross was carried out between these seven species, including self- and intraspecific pollinations using three pollination methods: normal pollination on the stigma, pollination on the ovary after cutting the style, and pollination on the stigma with the aid of ‘mentor’ (non-functional, compatible) pollen. Embryo rescue, starting 35 days after pollination, was applied to all interspecific combinations. The percentage of successful crosses was about 2.8% after normal pollination, 5.4% after cut-style pollination and 3.8% with the mentor pollen technique. Crosses with L. nepalense were exceptional in that embryos died during the embryo culture phase. Seventeen cross combinations (including 4 reciprocals) yielded 62 embryo plantlets from 839 interspecific pollinations.

Methods and strategies for detecting Solanum tuberosum dihaploids in interspecific crosses with S. phureja

SUMMARYThe frequency of dihaploid production following the interspecific pollination of Solanum tuberosum clones with Solanum phureja has been investigated. Seventeen hybrid combinations were tested and the crosses differed significantly in the number of seed produced, the proportions that were viable and the proportions that were dihaploid. The overall frequency of dihaploid production was 62%. The dominant embryo spot marker of the pollinator (IVP 48) in conjunction with seed diameter was used to classify the seed samples. Number of days taken to germinate was also recorded. It was therefore possible to examine retrospectively the effect of selecting sub‐sets of the seed based on the presence or absence of the embryo spot, seed size and germination time. A seed selection system based on the absence of the embryo spot in conjunction with seed greater than 1.25 mm in diameter resulted in 93.6% of the potential dihaploids being identified.

Hybrids by inter-specific pollination of Pinus muricata D. DON with P. pungens LAMB. and P. rigida MILL. in the genus Pinus

Hybrids by inter-specific pollination of Pinus muricata D. DON with P. pungens LAMB. and P. rigida MILL. in the genus Pinus

Angraecoid Orchids and Hawkmoths in Central Madagascar: Specialized Pollination Systems and Generalist Foragers

Angraecoid Orchids and Hawkmoths in Central Madagascar: Specialized Pollination Systems and Generalist Foragers

Pollen grain germination and pollen tube growth following in vivo and in vitro self and interspecific pollinations in annual Cicer species

Germination of pollen grains and growth of pollen tubes were studied to determine the cause of barreness in crosses among annual Cicer species. In vivo and in vitro time-course studies and fluorescent microscopy revealed no pollination incompatibility among the selfs, crosses and reciprocals of C. arietinum L., C. reticulatumLad. and C. cuneatumRich. In general, Cicer pollen grains germinated and grew on styles of Cicer species. Pollen tube growth was characterized by irregularly spaced and intermittent callose deposits. Failure of seed formation in interspecific pollinations may be attributed to the slowness of pollen tube growth or collapse of fertilized ovules. In addition to these causes, shortness of stamens and sparsity of pollen grains were responsible for flower drop in natural selfs. Although the number of pollen tubes entering the micropyle in interspecific pollinations was low, it may be possible to grow the fertilized ovules on an artificial medium to obtain F1 plants.

Pollen germination, pollen tube growth and fertilization following self and interspecific pollination of Paspalum species

Crossability between most Paspalum species is very low. This study was undertaken to identify the impediments to hybridization. Accessions of P. intermediumMunro. ex Morong, P. jurgensiiHackel and P. dilatatumPoir were self-pollinated and crossed with one anther. Paspalum intermedium is essentially self-sterile but P. jurgensii and P. dilatatum are highly self-fertile. Following pollination, pollen germination and tube growth were studied by observing the pollinated pistils with fluorescent microscopy. Examination of self-pollinated pistils revealed that the pollen germinated shortly after contacting the stigmas. Germination was over 80% for the P. intermedium and P. dilatatum accessions but only 57% for P. jurgensii. Pollen tubes grew to the micropyle within 45 minutes after pollination in P. dilatatum and 1 hour and 15 minutes in P. jurgensii. However, in the P. intermedium accessions most tubes did not grow beyond the stigma and very few penetrated the style and ovary. Apparently stylar-incompatibility is the reason for the low selfed seed set. In the cross-pollinations, pollen germinated shortly after pollination and germination ranged from 57 to 88% for the different crosses. In all crosses the pollen tubes grew to the micropyle within 30 minutes to 2 hours after pollination indicating that a cross-incompatibility system is not the cause for low crossability among these species. By examining embryo sacs from P. intermedium × P. dilatatum, its reciprocal and P. intermedium × P. urvillei crosses, it was determined that gametes failed to unite in some crosses and this is a major reason for low crossability.

Crocus sativus pollen germination and pollen tube growth in vitro and after intraspecific and interspecific pollination

The germination and tube growth of saffron (Crocus sativus L.) pollen were studied in vitro (in liquid media) and in vivo in pistils of Crocus sativus and Crocus thomasii after intraspecific and interspecific pollinations. In vitro about 20% of the saffron pollen grains germinated, but only about 9% developed a pollen tube. Although 21% of the pollen germinated on the stigmas, most pollen tubes ceased growth in the pistil and only a low percentage (about 6% of germinated grains) reached the ovary, where few of the ovules (about 5%) were penetrated. The defective germination and pollen tube growth were correlated with the occurrence of cytological abnormalities of the saffron pollen. Moreover, the ovarian transmitting tissue appeared to prevent the penetration of the ovules.

Reproductive Interactions Between Sympatric Dalechampia Species: Are Natural Assemblages "Random" or Organized?

By considering patterns of species co—occurrence and pollinator use, I attempted to answer the question: are natural assemblages of Dalechampia species (Euphorbiaceae) organized in ways that reduce the amount of interspecific pollination and/or competition for pollinator service? The observed structure was tested against three null models, one operating by species assemblage processes, one operating by species evolution processes, and a third operating by both processes. Two alternative operations definitions of sympatry were used with each model. The outcome (rejection or acceptance of the null hypothesis) was sensitive to the null model employed and the definition of sympatry used. This underscores the importance of using biologically realistic null models, assumptions, and definitions. Using the biologically more reasonable definition of sympatry, tests against all three null models suggest that assemblages of Dalechampia are structured with respect to pollinator use; indirect evidence suggests that some of this structuring has occurred through evolution of component taxa.

Pollination Ecology of the Spring Wildflower Community of a Temperate Deciduous Forest

I studied the spring wildflower community of mesic deciduous forests in piedmont North Carolina to determine (a) the extent to which fecundity is pollination—limited in the community, (b) the importance of competition for pollination in affecting seed—set, and (c) the characteristics of plants and their floral visitors that most contribute to full pollination. Although inadequate pollination seems likely in the community, supplemental hand—pollination significantly improved fecundity in just 3 of the 12 species I examined. Pollination—limited reproductive success was evident only in a distinctive subset of the community, species pollinated primarily by queen bumble bees. The majority of wildflower species are pollinated by flies and solitary bees. Measurements of visitation rates and pollinator effectiveness on these plants confirmed that they are usually adequately pollinated in spite of a short blooming season, considerable overlap in flowering times, extensive pollinator sharing by concurrently blooming species, and inclement weather that frequently interrupts insect activity. Many of the flies and solitary bees are inconstant foragers, yet competition for pollination among wildflower species through differential pollinator attraction or interspecific pollinator movements usually does not significantly decrease the seed—set of plants with shared visitors. Competition may act with other causes of insufficient pollination, however, as a selective force to maintain a characteristic set of floral biology traits within the community, including autogamy and self—compatibility, extended receptivity, and pollination by a variety of visitor types. That these floral traits contribute significantly to the successful pollination of vernal herbs was demonstrated by observations of visitor behavior, plant caging experiments that excluded visitors or restricted their access to selected flowers, and measurements of floral lifetimes and seed—set for individual plants. These traits are effective regardless of the source of pollination—limited fecundity, and it is the prevalence of such traits, rather than floral specialization or character displacement, that distinguishes the forest spring wildflower community from other communities with potentially inadequate pollinator service.

Crossability in interspecific pollinations among species of hard pine in the genus Pinus

Crossability in interspecific pollinations among species of hard pine in the genus <i>Pinus</i>

Overgrowth of Pollen Tubes in Embryo Sacs of Rhododendron Following Interspecific Pollinations

Frequent overgrowths of pollen tubes within the embryo sac are characteristic of a number of interspecific crosses in the genus Rhododendron (Ericaceae). The combined techniques of sectioning, squashing and whole-ovule clearing have confirmed that in ovules showing this phenomenon the pollen tube fails to terminate growth and release sperms on entry into a synergid; instead it continues to grow beyond the synergid and egg cell, often filling the main body of the embryo sac with a coiled and distorted mass. Such ovules fail to develop further. The occurrence and possible causes of this error syndrome are discussed.