Pollen tetrad segregation and pollen ovule ratios in six species of Acrotriche (Styphelioideae: Ericaceae)

Pollen morphology can be useful in the determination of phylogeny and mating systems of plants. Pollen ovule ratios can give an indication of the mating system of plant species, and there are a number of theories as to reductions in response to pollination strategies. Pollen tetrad segregation occurs when a number of pollen grains within a tetrad abort; this process has evolved a number of times in the family Ericaceae. Pollen ovule ratios along with the total number of tetrads, number of viable grains and proportions of each of the tetrad types were investigated in six species of Acrotriche (Styphelioideae: Ericaceae). Pollen ovule ratios were used in comparison with related species to give indications of mating systems and to examine theories regarding reductions in pollen production. The study species can be arranged into distinct groupings based on the proportions of tetrad types that correlate with floral morphology and may be indicative of phylogentic associations.     

Nutlet morphology in Hemigenia R.Br. and Microcorys R.Br. (Lamiaceae)

Nutlets of Hemigenia R.Br. and Microcorys R.Br. were examined using SEM. Significant variation, mainly useful at the infrageneric level, was found in nutlet shape, nature of the attachment scar, nature of surface sculpturing, exocarp cell shape and sculpturing, and nature of the indumentum. Typical nutlets are ovoidal, strongly reticulate or rugose. The exocarp cells are isodiametric and convex to papillate. Also common are cylindrical nutlets, often with longitudinal ridging and papillate exocarp cells. Surface pitting and concave exocarp cells are rare. A cladistic analysis of nutlet characters suggests both Hemigenia and Microcorys are polyphyletic, and Microcorys paraphyletic with respect to Westringia Sm. Notwithstanding that, the infrageneric classification of Hemigenia was largely supported, while in Microcorys, there was support for sect. Hemigenioides, but sects Anisandra and Microcorys were not resolved as distinct.     

Observations of high genetic variability in the endangered Australian terrestrial orchid Pterostylis gibbosa R. Br. (Orchidaceae)

The genetic variation in all known populations of an endangered Australian native terrestrial orchid Pterostylis gibbosa R.Br., was investigated with starch gel electrophoresis. A total of 16 isozyme loci were assayed. The percentage of polymorphic loci (P), the number of alleles per locus (A), observed and expected heterozygosity at population levels were 69%, 2.21, 0.210, 0.261, respectively. The G(st) value of 15% indicates that around 85% of variation resides within populations. Despite isolation by distance most alleles were distributed across most of the populations. High genetic variability along with low population divergence may be the result of recent population fragmentation or from extensive gene flow maintained by seed and pollen movement. To investigate whether poor seed viability contributed towards its rarity, an orchid seed viability test using Fluorescein diacetate revealed high seed viability (range 68-90%). Although endangered and restricted to only four geographical areas, P. gibbosa showed a higher level of genetic variation than other orchids with larger populations.     

The genus Sarcostemma R.Br. (Asclepiadaceae) in Madagascar

The Madagascar! representatives of the genus Sarcostemma are investigated. All Malagasy material studied can be assigned to four taxa. S. viminale ssp. viminale occurs in Madagascar as well as on other islands along the African coast and on the African mainland: the other three species are endemic to Madagascar. All four species occur in the southern, arid part of the island, to which S. decorsei is endemic. S. membranaceum and S. elachistemmoides are new. All species are described and illustrated and a key and distribution maps are presented.     

Early-acting inbreeding depression in three species of Vaccinium (Ericaceae)

Greenhouse pollinations were performed to determine whether early-acting inbreeding depression is contributing to low levels of self-fertility in three Vaccinium species: V. myrtilloides Michaux, V. angustifolium Aiton, and V. corymbosum L. All three species showed a significant reduction in self fruit set and in the proportion of fertilized ovules that developed into mature seed in self compared to outcross fruit. Reductions were more severe in V. myrtilloides and V. angustifolium than in V. corymbosum; however, early-acting inbreeding depression appeared to be the primary factor limiting self-fertility in all three species. Evidence for early- acting inbreeding depression included the presence and higher proportion of aborted ovules in self fruit than in outcross fruit, a correlation between levels of self and outcross seed set, and pollen chase experiments demonstrating that self-pollen does fertilize the ovules. Self-fertility in the three species was probably influenced by levels of genetic load, ploidy level and outcrossing rates. Received: 10 December 1999 / Revision accepted: 20 June 2000     

Evolution of hybrid taxa inNasturtium R.Br. (Brassicaceae)

Nasturtium officinale (2n=4x=32),N. microphyllum (2n=8x=64) andN. ×sterile (2n=6x=48) have been investigated by isozyme analyses to study evolutionary processes withinNasturtium. Four additional species assumed to be involved in the formation of the octoploidN. microphyllum (Rorippa amphibia, R. sylvestris, R. palustris, andCardamine amara) were also examined. A total of 641 individuals were analyzed for six isozyme systems (alcohol dehydrogenase, aspartate aminotransferase, glutamate dehydrogenase, leucine aminopeptidase, malate dehydrogenase, and phosphoglucoisomerase). Eleven gene complexes coding for 43 allozymes were detected. Fifteen alleles were observed inN. officinale, twelve of them being fixed. All alleles fixed inN. officinale were also present and fixed inN. microphyllum. Seven additional fixed alleles were observed inN. microphyllum. The presence of these seven alleles inRorippa taxa provide evidence for an allopolyploid origin ofN. microphyllum withN. officinale and aRorippa taxon involved.C. amara is not a parent species ofN. microphyllum. N. ×sterile showed a fixed banding pattern which was identical to that ofN. microphyllum. It is argued thatN. ×sterile is a hybrid betweenN. officinale andN. microphyllum. Human impact has played a major role in the evolution ofN. ×sterile. The formation and persistence of the hybrid were influenced by introducingN. officinale into the natural distribution area ofN. microphyllum and by creating ditches and ponds where due to its vegetative capabilitiesN.×sterile could establish.     

Epacris crassifolia R. Br. (Epacridaceae) - A Reappraisal

Epacris crassifolia R. Br.s. lat.,as represented in collectionsat G, BM, HO, NSW, MEL, CBG and CAN, has been redefined as threeseparate species. The common lax, prostrate form includes twosubspecies,E. crassifoliassp.crassifoliaR. Br.stat. nov. andE.crassifoliassp.macrofloraCrowden et Menaduessp. nov.separatedon floral morphology.E. pinoideaCrowden et Menaduesp. nov.andE.lithophilaCrowden et Menaduesp. nov.are erect and woody, beingdistinguished on leaf and floral characters. Epacridaceae; Epacris crassifolia ; Epacris lithophila; Epacris pinoidea; new species     

Environmental and hormonal regulation of seed dormancy and germination in Cape fynbos Leucospermum R.Br. (Proteaceae) species

The endogenous levels of abscisic acid (ABA), cytokinins (CKs) and gibberellins (GA₁/GA₃ combined) in Leucospermum glabrum embryos were monitored in axes and cotyledons separately during normal germination. Plant growth substance changes were correlated with known morphological, structural and ultrastructural events in the embryo of Proteaceae. The effect of exogenous application of 6-benzyladenine (BA) and GA₄₊₇ under three known dormancy-enforcing environmental conditions were studied in L. glabrum and L. cordifolium. The endogenous levels of the hormone classes GAs and CKs changed phasically during normal germination under a single alternating temperature regime. GA₁/GA₃ levels increased in cotyledons within 3 d of hydration while at the same time initial CK levels decreased. Following this transient peak GAs fell to a low level throughout the germinative period. Subsequently the CKs, Z and ZR, and to a lesser extent their dihydro-derivatives, appeared in both the axes and the cotyledons as fluctuating, transient peaks. Early increases in GAs are thought to control the induction of the germination process. The CK pattern suggests that CKs control at least three major processes of germination sensu stricto following induction: 1) early mobilization of protein and lipid reserves in the axis and later in cotyledons, 2) cotyledon expansion which causes the endotesta to split permitting radicle protrusion and 3) later, radicle growth.Our results indicate that dormancy in intact Leucospermum seeds is enforced by embryo anoxia, regulated by the impermeable exotesta. In addition synthesis of or tissue sensitizing to both hormone classes GAs and CKs depends on moderately low temperature as the primary environmental requirement. For GA synthesis a secondary, daily pulse of high temperature is required. Inhibitory hormones, specifically ABA, appear not to play a role.Abbreviations ABA Abscisic acid - BA 6-benzyladenine - CK Cytokinin - DHZ Dihydrozeatin - DHZR Dihydrozeatin riboside - GA Gibberellin - HPLC High performance liquid chromatography - iP Isopentenyladenine - IPA Isopentenyladenosine - PGS Plant growth substance - RIA Radioimmunoassay - Z Zeatin - ZR Zeatin riboside     

Uraecium landolphiae (Uredinales), a new species on Landolphia dulcis (R. Br. ex Sabine) Pichon var. dulcis

A new species of rust fungus, Uraecium landolphiae on Landolphia dulcis (R. Br. ex Sabine) Pichon var. dulcis (Apocynaceae) is described from Nigeria. It is characterized by pronounced, thick-walled spores and capitate paraphyses.     

Infrageneric combinations in Gaultheria L. (Ericaceae)

MIDDLETON, D. J., 1992. Infrageneric combinations in Gaultheria L. (Ericaceae). Sections Pseudogaultheria and Brossaea and series Leucothoides and Gymnobotrys , previously invalidly published new combinations in Gaultheria , have been validated.     

Morphogenetic potential of foliar explants in Duboisia myoporoides R.Br. (Solanaceae)

The effects of serial combinations of either indole-3-acetic acid, indole-3-butyric acid or -naphthaleneacetic acid (0.5–10.0 mg/l) with either kinetin, 6-benzyl-amino-purine, zeatin or 6-methylaminopurine (0.5–5.0 mg/l) have been investigated to assess the morphogenetic potential of foliar explants of Duboisia myoporoides. Shoot buds developed either directly or via a callus interphase. Combinations involving indole-3-acetic acid with any of the cytokinins were more effective in inducing shoot bud formation compared to those containing indole-3-butyric acid or -napthalenacetic acid as an auxin. Among cytokinins, zeatin, kinetin and 6-benzylamino-purine were equally effective for shoot formation. However, optimum response with zeatin could be achieved at low concentrations (0.5–2.0 mg/l), while kinetin and 6-benzylamino-purine exhibited comparable efficacy at higher levels (3.0–5.0 mg/l). 6-Methylaminopurine proved least effective in all concentrations and combinations tested. Rooting of the differentiated shoots was readily achieved with -naphthaleneacetic acid alone (0.5 mg/l) after changing the physical form of the medium from gel to static liquid. Regenerated plantlets were transferred to pots and grown to maturity in the field with a high rate of survival (80–90%).Abbreviations BAP 6-benzylaminopurine - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MAP 6-methylaminopurine - MS Murashige and Skoog (1962) medium - NAA -naphthaleneacetic acid - PVP polyvinyl pyrrolidone     

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).     

Development of ovule, megagametophyte and early endosperm in representative species of Rhododendron L. (Ericaceae)

PALSER, B. F., PHILIPSON, W. R. & PHILIPSON, M. N., 1989. Development of ovule, megagametophyte and early endosperm in Rhododendron L. (Ericaceae). Complete development of ovule, megagametophyte and early endosperm is compared for 15 species (almost complete for four additional species) representing all subgenera and most sections of Rhododendron. In all the ovule is anatropous, unitegmic, tenuinucellate with the lateral and micropylar nucellus disintegrating completely. The integument has a tanniniferous epidermis, starch around egg apparatus and micropyle, an endothelium and hypostase. Differences occur in time of closure of the micropyle and its final length, total proportion of ovule occupied by gametophyte and by formation of ovule tails only in section Vireya. Megagametophyte development follows the Polygonum pattern in all species. A single archesporial cell becomes the megaspore mother cell directly, and the chalazal spore of a linear tetrad functions. Between the eight-nucleate stage and maturity the micropylar end of the gametophyte elongates into the micropyle. Starch is characteristically present in the mature central cell. The pollen tube penetrates porogamously and double fertilization is rapid. Endosperm development starts promptly and is cellular, first forming a linear row of four cells. The zygote elongates slightly but does not divide during the stages followed. Differences may occur in time of enlargement, orientation of some mitoses, some cellular characteristics, amount of starch present and final size of megagametophyte. Rare abnormalities occur.     

Pollen limitation in three sympatric species ofVaccinium (Ericaceae) in the Upper Ardennes, Belgium

The reproductive success of three co-flowering species ofVaccinium (V. myrtillus, V. vitis-idaea andV. uliginosum) was studied in one heathland of the Upper Ardennes, Belgium, during three years (1988–1990). The purpose was to examine whether pollen limitation, flower position and flowering phenology may influence patterns of fruit set in these three sympatric species. I quantified fruit and seed set following supplementary hand-pollinations and compared this to natural fruit set. On the same plants, I also quantified fruit and seed set in relation to the spatial position of the flowers on the ramet and their temporal sequence of blooming. Hand-pollination had no significant effect on fruit set inV. vitis-idaea andV. uliginosum, but significantly increased seed number per fruit in 1989. InV. myrtillus both fruit and seed set were increased by supplementary pollination, but significantly in only one year. Analyses of position effects revealed that the fruits in the lower positions in the ramet did not mature preferentially and did not contain more seeds inV. uliginosum and inV. vitis-idaea. Flowering phenology also had no significant effect for these species. InV. myrtillus hand-pollinated flowers showed a seasonal decline in seed number, and control (naturally pollinated) flowers showed a seasonal increase in fruit set. Fruit and seed set appear to be pollen-limited rather than resource-limited inV. uliginosum. In the two other species, unfavorable weather (frosts) could be a more important cause of low fruit and seed set.     

Comparison of genetic variability in remnant and wide-spread rainforest understorey species of Austromyrtus (Myrtaceae)

This study investigated the genetic variability, stand structure, and reproductive activity of four species of Austromyrtus which showed differing levels of rarity and patterns of distribution. The focus of the study was A. gonoclada which is extremely rare due to extensive urban expansion in Brisbane, Australia. The total number of known individuals in the species is only 27. Because nothing was known about the genetic structure of Austromyrtus comparison with other species was made to provide a context for studies on A. gonoclada. Population structure and levels of reproductive activity were not correlated to species rarity or distribution. A. gonoclada showed maximum genetic variability in comparison to the other species of Austromyrtus, despite the small population size. Three of six variable loci were in Hardy-Weinberg equilibrium in A. gonoclada populations, in contrast to populations of the other species which had few heterozygous genotypes. The higher variability of the remaining individuals is suggested to be a legacy of the relatively short time since they were part of a larger population. There were very few seedlings of A. gonoclada, in contrast to the other species of Austromyrtus and the seeds produced fell from the tree while still green and were unable to be germinated. A. gonoclada is under continuing threat from development and has low reproductive success. Active programmes for recovery of this species will be necessary as its continued survival is dependent on population increase. Management of the genetic resources of the species will enable survival with long-term evolutionary potential.     

Pollen Tube Growth and Seed Set of Banksia coccinea R.Br. (Proteaceae)

Controlled hand pollinations and field observations were usedin conjunction with fluorescence and scanning electron microscopyand fruit and seed set to investigate the timing of stigma receptivity,pollen tube growth and self-incompatibility in relation to fertilityin B. coccinea. The species showed both protandry and partialself-incompatibility. Peak stigma receptivity as measured bypollen germination was recorded at 3 d after anthesis and maximumproduction of stigmatic exudate at 6 d. Pollen tubes reachedthe base of the style by 6 d after pollination. A 5 x 5 diallelexperiment was conducted and the results measured by pollentube growth. Self-pollinations generally resulted in poorertube growth than crosses and there was significant specificand general combining ability as well as reciprocal effects.Cross-pollination resulted in improved fruit set and seed toflower ratio over both selfing and open pollination. Spatiallimitations to fertility due to infructescence size were alsorecorded, but the combination of outcrossing mechanisms andspatial limitation did not entirely account for the low fertility.It is suggested that environmental conditions and the availabilityof resources may also exert an influence. Banksia coccinea R.Br., scarlet banksia, Proteaceae, pollination, stigma receptivity, pollen tube growth, self-incompatibility, breeding system, seed set