conservation concerns. Several examples can be taken from Rhododendron, where many species have been studied that are native to Asia ( Li et al. 2015 ; Wu et al. 2015 ; Zhao et al. 2012 ) and North America ( Chappell et al. 2008 ). These studies determined
). Viburnum rufidulum , one of the 12 species native to North America ( U.S. Department of Agriculture, 2008 ), is a small deciduous tree capable of growing to a height of about 3.0 to 9.0 m ( Dirr, 2007 ). Cymes of small white flowers attract a variety of
Nineteen native blueberry (Vaccinium ashei Reade) clones selected from several areas in northern Florida and southeastern Georgia were self- and cross-pollinated in a greenhouse. Fruit set for the 19 clones averaged 15% after self-pollination and 58% after cross-pollination. Viable seeds per berry averaged four for self-pollination and 11 for cross-pollination. Average berry weight was 0.7 g for self-pollination and 1.1 g for cross-pollination, and average interval from flowering to ripening was 106 days for selfing and 92 days for crossing. Following self-pollination, pollen germinated and pollen tubes grew down the style as rapidly as after cross-pollination.
the result of the broad range of flowering times, panicle size, leaf width and color, and plant form of modern cultivars, which allows for their use in horticultural applications ranging from formal gardens to informal native urban landscapes ( Wilson
The relationship was analyzed between historical annual rainfall and pecan [Carya illinoinensis (Wangenh.) K. Koch] homogeneity in selected hardwood populations along two river systems in the native habitat of the species. Tree species other than pecan (sympatric species) were more abundant with increasing rainfall in that the more homogenous pecan populations were located in geographic areas with the least rainfall. These results are the first to establish that pecan stand homogeneity across geographic areas is inversely related to the amount of annual rainfall. Variation in soil texture within geographic areas was also strongly correlated with variation in pecan homogeneity and pecan density. Pecans occur principally on loamy bottom lands and grow on clayey bottom lands in less abundance. A hypothesis related to growth partitioning between root and shoot is proposed to account for pecan's survival advantage, and thus higher stand homogeneity, with decreasing rainfall in native pecan areas. Conversely, the decrease in stand homogeneity with increasing rainfall is proposed to be due to increased forestation of sympatric species on clayey sites that are not optimum for pecan. Across the rainfall gradients, pecan's shade intolerance is suggested to be minimized by differential site requirements for pecan and its sympatric species.
Understanding physiological drought resistance mechanisms in ornamentals may help growers and landscapers minimize plant water stress after wholesale production. We characterized the drought resistance of four potted, native, ornamental perennials: purple coneflower [Echinacea purpurea (L.) Moench], orange coneflower [Rudbeckia fulgida var. Sullivantii (Beadle & Boynt.) Cronq.], beebalm (Monarda didyma L.), and swamp sunflower (Helianthus angustifolius L.). We measured a) stomatal conductance of leaves of drying plants, b) lethal water potential and relative water content, and c) leaf osmotic adjustment during the lethal drying period. Maintenance of stomatal opening as leaves dry, low lethal water status values, and ability to osmotically adjust indicate relative drought tolerance, with the reverse indicating drought avoidance. Echinacea purpurea had low leaf water potential (ψL) and relative water content (RWC) at stomatal closure and low lethal ψL and RWC, results indicating high dehydration tolerance, relative to the other three species. Rudbeckia fulgida var. Sullivantii had a similar low ψL at stomatal closure and low lethal ψL and displayed relatively large osmotic adjustment. Monarda didyma had the highest ψL and RWC at stomatal closure and an intermediate lethal ψL, yet displayed a relatively large osmotic adjustment. Helianthus angustifolius became desiccated more rapidly than the other species, despite having a high ψL at stomatal closure; it had a high lethal ψL and displayed very little osmotic adjustment, results indicating relatively low dehydration tolerance. Despite differences in stomatal sensitivity, dehydration tolerance, and osmotic adjustment, all four perennials fall predominantly in the drought-avoidance category, relative to the dehydration tolerance previously reported for a wide range of plant species.
A total of 118 Pyrus sp. (pear) and cultivars native mainly to east Asia were subjected to randomly amplified polymorphic DNA (RAPD) analysis to evaluate genetic variation and relationships among the accessions. Two hundred fifty RAPD markers were scored from 20 decamer primers. RAPD markers specific to species were identified. Clustering analysis revealed two divisions: one comprising cultivars of P. communis L., and the other including all accessions of Pyrus native to east Asia. The grouping of the species and cultivars by RAPD data largely agrees with morphological pear taxonomy. However, some noted incongruence existed between two classification methods. Pyrus calleryana Dcne. clustered together with P. koehnei Schneid., P. fauriei Schneid. and P. dimorphophylla Makino. Pyrus betulaefolia Bge. clustered with P. ×hopeiensis Yu and P. ×phaeocarpa Rehd. A noncultivated clone of P. aromatica Kikuchi et Nakai grouped with P. aromatica cultivars. Pyrus hondoensis Nakai et Kikuchi and cultivars of P. ussuriensis Max. formed a single group. Some accessions from Korea (named Korean pear) had species-specific RAPD markers and comprised an independent group. Most of the Chinese white pears clustered together with most of the Chinese sand pears. Based on the present results, the new nomenclature P. pyrifolia var. sinensis (Lindley) Teng et Tanabe for Chinese white pear was suggested. Most accessions of Japanese pears fell into one main group, whereas pear cultivars from Kochi Prefecture of Japan subclustered with some Chinese sand pears and one accession from Korea. Our results infer that some local Japanese pear cultivar populations may have been derived from cultivars native to Kochi Prefecture in Shikoku region, and that the latter may have been introduced from ancient China and/or Korea.
Fruit color of selections of native V. elliotti Chapm. varied from black to blue. Wax on fruit was occasionally found to be globular in form but most often waxes were found to range from flat plates to upright platelets and from horizontal rods to long upright rods. Combinations of wax forms occurred in varying densities on the fruit of native selections. Upright rods and platelets accounted for the blue fruit color. Mature black fruit usually had a limited amount of platelet wax and no rodlet structures. β-Diketones were absent or nearly absent on these mature black fruit. Black fruit had some of the higher weight loss measurements. The paraffin content of the fruit wax was relatively high at one location for some black selections and appeared to reduce weight losses of these selections to levels similar to the bluer selections. Leaves had only globular wax forms, less wax than fruit, and considerable variation in the density of acerate trichomes. Leaf hair density and distribution on leaves was independent of variation in wax forms on fruit.
Variation in 14 horticultural traits of native octoploid Fragaria L. from North and South America was examined in a greenhouse. Significant levels of variation were found for all but a few of the traits at the species, subspecies, regional and genotypic level, with the highest amount of variation generally being partitioned among genotypes. Fragaria chiloensis (L.) Miller was superior to F. virginiana Miller for crown number, fruit weight, soluble solids and seed set, while Fragaria virginiana was superior for runner production, peduncle length, fruit number, fruit color and winter hardiness. Fragaria chiloensis ssp. pacifica Staudt had the highest soluble solids and among the earliest bloom dates, highest crown numbers and highest seed set. Fragaria chiloensis ssp. chiloensis f. chiloensis (L.) Duch. produced the largest fruit and among the earliest bloom dates and longest peduncles. Fragaria chiloensis ssp. chiloensis f. patagonica (L.) Duch. had among the highest crown numbers and the highest percentage seed set. Fragaria virginiana ssp. platypetala (Rydb.) Staudt produced the most crowns and its fruit ripened earliest. Fragaria virginiana ssp. glauca (Wats.) Staudt were the latest flowering, had the darkest fruit color and the most flowering cycles. Fragaria virginiana ssp. virginiana Duch. displayed the most winter dieback, the longest peduncles, and the highest flower and runner numbers. No significant differences were observed in any of the examined traits between F. chiloensis ssp. pacifica and F. chiloensis ssp. lucida, or F. virginiana ssp. grayana and F. virginiana ssp. virginiana. A number of individual genotypes were superior for more than one trait. CFRA 0024 possessed unusually high crown numbers, was extremely early blooming and displayed multiple fruiting cycles. CFRA 1121 had unusually long peduncles and much higher than average values for fruit weight, soluble solids, fruit color and seed set. CFRA 0094 was extremely early flowering and had much darker fruit color than most other F. chiloensis genotypes. CFRA 0368 flowered unusually early and had among the largest fruit. CFRA 0366 possessed unusually long peduncles and the largest fruit of any North American genotype. CFRA 0560 and CFRA 1369 had an unusual combination of multiple flowering cycles and high runner production. CFRA 1170 and 1171 were unusually late fruiting and had high numbers of large fruit on long peduncles. CFRA 1385 and JP 95-3-1 had extremely high flower numbers, long peduncles and large fruit.
Seedlings from 21 collections of the native North American red raspberry, Rubus idaeus strigosus (Michx.), were screened for reaction to Amphorophora agathonica Hottes, the aphid vector of the red raspberry mosaic virus complex. Sixty-four seedlings from 1,041 screened were selected for resistance to colonization. Three of these were intercrossed and also crossed with 2 cultivars of R, i. vulgatus Arrhen origin to produce F1 progenies. Inheritance of the resistance reaction in the 3 selected seedlings appeared to be controlled by 2 dominant complementary genes. These genes, which are designated Ag2 Ag3, do not appear to give as high a level of resistance to the aphid as gene Ag1, which is of R. i. vulgatus origin and gives virtual immunity. It is suggested that genotypes combining Ag, with Ag2 and Ag3 might be of value in reducing genetic vulnerability if virulent biotypes of A. agathonica appear. Screening for reaction to the aphid under laboratory conditions, prior to field planting, eliminated large numbers of susceptible seedlings. Additional screening in the field the year of planting eliminated more. Segregation ratios, which had been adjusted from the field results, gave better agreements than laboratory screenings alone to the proposed hypotheses.