LIFETIME BIOMASS PARTITIONING AND YIELD COMPONENT RELATIONSHIPS IN THE HIGHBUSH BLUEBERRY,VACCINIUM CORYMBOSUM L. (ERICACEAE)

The proportion of annual biomass production allocated to various vegetative and reproductive tissues was measured in differently aged individuals of Vaccinium corymbosum from native populations in southern Michigan. The relationship between age and allocation was determined and a lifetime pattern of biomass partitioning was developed. The proportion of biomass allocated to reproduction was higher than many have predicted for woody species, and the relationship between age and reproductive effort did not conform to optimality models. In addition, reproductive performance was not affected by previous growth or reproduction. The basis of this complex reproductive behavior was examined by quantifying the relationships among components of reproduction. In general, yield components behaved independently within a season. A high potential reproductive effort coupled with yield component independence may be an adaptation to fluctuating environments.     

POPULATION GENETIC STRUCTURE IN DIPLOID BLUEBERRY VACCINIUM SECTION CYANOCOCCUS (ERICACEAE)

Vaccinium section Cyanococcus comprises diploid, tetraploid, and hexaploid species (x = 12) all of which are highly self-sterile. In order to assess the distribution of genetic variation within and among the diploids, population genetic analyses of allozyme data were conducted on three species: V. elliottii, V. myrtilloides, and V. tenellum. Populations were located throughout the range of these taxa in eastern North America. Data were collected at 20 loci, 12 of which are mendelian based on formal genetic analyses. Consistent with expectations for out-crossing taxa, these species exhibited high levels of variation within populations. Eighteen loci were polymorphic with the number and frequency of alleles varying among taxa. Mean values for the number of alleles per polymorphic locus, proportion of polymorphic loci, and expected heterozygosity were 2.8, 48.2, and 0.148, respectively. High infraspecific genetic identities exceeding 0.9 indicated that these taxa are homogeneous. All populations were in Hardy-Weinberg equilibrium with slight heterozygote excess observed in V. myrtilloides and V. tenellum. Although total genetic diversity was lower than that observed for other predominantly out-crossing species, it was apportioned similarly. The majority could be attributed to differences among individuals within populations. Conspecific populations were relatively undifferentiated with genetic differentiation similar to other self-incompatible species.     

DEMOGRAPHIC SOURCE-SINK DYNAMICS RESTRICT LOCAL ADAPTATION IN ELLIOTT'S BLUEBERRY (VACCINIUM ELLIOTTII)

In heterogeneous landscapes, divergent selection can favor the evolution of locally adapted ecotypes, especially when interhabitat gene flow is minimal. However, if habitats differ in size or quality, source-sink dynamics can shape evolutionary trajectories. Upland and bottomland forests of the southeastern USA differ in water table depth, light availability, edaphic conditions, and plant community. We conducted a multiyear reciprocal transplant experiment to test whether Elliott's blueberry ( Vaccinium elliottii ) is locally adapted to these contrasting environments. Additionally, we exposed seedlings and cuttings to prolonged drought and flooding in the greenhouse to assess fitness responses to abiotic stress. Contrary to predictions of local adaptation, V. elliottii families exhibited significantly higher survivorship and growth in upland than in bottomland forests and under drought than flooded conditions, regardless of habitat of origin. Neutral population differentiation was minimal, suggesting widespread interhabitat migration. Population density, reproductive output, and genetic diversity were all significantly greater in uplands than in bottomlands. These disparities likely result in asymmetric gene flow from uplands to bottomlands. Thus, adaptation to a marginal habitat can be constrained by small populations, limited fitness, and immigration from a benign habitat. Our study highlights the importance of demography and genetic diversity in the evolution of local (mal)adaptation.     

POLLINATION ECOLOGY OF VACCINIUM STAMINEUM (ERICACEAE: VACCINIOIDEAE)

Successful fruit set by deerberry, Vaccinium stamineum (Ericaceae: Vaccinioideae) requires floral visitation by insects, and in particular by bees that collect its pollen by sonication of anthers (“buzz-pollination”). A diversity of bees visit deerberry flowers, but most species are either 1) infrequent, 2) polylectic (broad host range for pollen), or 3) principally nectar-seeking, and so are unimportant as pollen vectors. Both sexes of the solitary, oligolectic bee Melitta americana⁵ (Melittidae) are abundant at flowering deerberry bushes in central New York State. Female M. americana sonicate the deerberry anthers while imbibing nectar, and carry virtually pure scopal loads of deerberry pollen, unlike the other common visitor, Xylocopa virginica (Anthophoridae). Comparative analyses of bee 1) abundances, 2) buzz-pollination behaviors, 3) pollen fidelities, and 4) pollination efficiencies, all indicate that Melitta americana is the primary pollinator of Vaccinium stamineum.     

GENETIC LOAD AND THE MATING SYSTEM IN HOMOSPOROUS FERNS

The mutational genetic load was calculated assuming mutation-selection-inbreeding equilibrium and applied to homosporous ferns. Diploid species with past inbreeding should have a low genetic load while outcrossers should have a high genetic load. These predictions are consistent with the bimodal pattern of genetic load found in 18 diploid homosporous fern species. The prediction that tetraploids should have a low genetic load is also consistent with estimates of genetic load in several species.     

THE POLLINATION ECOLOGY OF ZENOBIA (ERICACEAE)

Zenobia is a shrub endemic to the coastal plain of the Carolinas and southeastern Virginia. The sole species, Zenobia pulverulenta, appears to be weakly self-compatible and partially self-pollinating. Fruit set was reduced, but not eliminated by excluding insect floral visitors. Insect visitors were collected and their pollen loads examined for Zenobia and foreign pollen. Analysis of these pollen loads and observations of insect-foraging behavior indicate that workers of three species of bumblebee (Bombus bimaculatus, B. griseocollis and B. impatiens) are. the principal pollinators of Zenobia. However, pollinator density and composition appear to be strongly influenced by the habitats in which Zenobia grows. Pollen and nectar serve as the primary rewards for pollinators.     

GENETIC LOAD IN OSMUNDA REGALIS POPULATIONS

Osmunda regalis sporophytes form haploid spores which develop into functionally hermaphroditic gametophytes. The self-fertilization of such gametophytes results in zygotes which are completely homozygous. Spore samples collected from sporophytes in natural populations were used to establish gametophyte cultures. The majority of these gametophytes were unable to form viable embryos when only self-fertilization was possible. Controlled selfing and crossing experiments revealed that the inability of these homozygous embryos to develop normally is attributable to the presence of recessive lethals. To account for this genetic load, an hypothesis is proposed integrating the morphology and ecology of the gametophyte generation with the polyploid genetic system of the sporophyte generation.     

Effect of pollen load size and source (self, outcross) on seed and fruit production in highbush blueberry cv. 'Bluecrop' (VACCINIUM CORYMBOSUM; Ericaceae)

Reproductive fitness of a plant is ultimately determined by both number and quality of seed offspring. This is determined by sexual selection of pollen microspores and ovules during pollination and fertilization. These processes may include pollen competition and seed abortion, which reduce the number of microspores and ovules available for final seed production. Thus, even an excess of pollen microspores to ovules does not result in fertile seeds equal to ovule number. We investigated pollen requirements of highbush blueberry (Vaccinium corymbosum cultivar 'Bluecrop') for maximal seed production and how fertile seed number translates into fruit quality, since fruit quality would ultimately determine the dispersal of its offspring. We demonstrate that individual blueberry flowers with a mean of 106 ovules reach their maximum fruit set and mass and minimum time to ripen when 125 outcross pollen tetrads pollinate a flower, compared to 10 or 25. Three hundred tetrads resulted in the increase of fertile seeds, but did not result in a further increase of fruit mass or fruit set, or decrease in time to ripen. We also examined the effect of pure and mixed loads of self and outcross pollen (25 and 125 tetrads), and found no differences in fertile seed number, fruit mass, or percentage fruit set when pollen loads were either 25 self or outcross pollen tetrads, although number of days to ripen was significantly shorter by 8 d with 25 outcross tetrads. When the pollen load of 125 tetrads consisted of self or a 50:50 mixture of self and outcross pollen, fruit mass, days to ripen, and percentage fruit set were not different from loads of 125 outcross pollen. In addition, a pollen load of 25 outcross tetrads resulted in fertile seed number and fruit quality in between that of 25 self, and 125 self, 125 mixed, or 125 outcross tetrads. Large, small, and flat seed types were identified, and only large seeds (length = 1.7 mm) were fertile. These results improve our understanding of pollen load size and source requirements of a crop plant and the limits to pollen transfer when translated to fruit growth.     

中国蓝浆果生产现状

全面报道了蓝浆果(Vaccinium L.spp.)在中国的生产情况,共分为南、北两大区域.北区是指以吉林省为主的东北地区,南区指长江以南广阔的酸性红壤土地区.果用野生种只分布在东北地区.自20世纪80年代起开始引种欧美栽培品种,共达60余个.在北区以吉林农业大学为主,在南区以江苏省·中国科学院植物研究所为主,采用组培和扦插方法繁殖,南、北两区均各有年产百万株以上苗木的能力.在南、北两区的适宜地区,如吉林、江苏和贵州等省,都已选出各自的适栽品种,栽培后的产量和果实质量分别均可达到国外优良水平,显示了蓝浆果在中国发展的巨大前景.