Flow cytometric analysis of somaclonal variation in lineages of Hosta sports detects polyploidy and aneuploidy chimeras

Somaclonal variation of some 124 specially selected cultivars of Hosta Tratt. (Hostaceae) was investigated. Nuclear DNA contents (2C‐value) were measured by flow cytometry of leaves and roots of L1, L2 and L3 layers derived from apical meristems. These values were then converted to inferred ploidies by comparing the measured 2C‐values and ploidy with those of the parent plant. During tissue‐culture propagation, on occasion diploid (L1‐L2‐L3 = 2‐2‐2) hostas give rise to polyploids, such as fully tetraploids (4‐4‐4), and periclinal chimeras, such as partial tetraploids (4‐2‐2). Continual propagation can result in partial tetraploids becoming full tetraploids. Nuclear DNA of some diploids increased with incomplete chromosome sets resulting in fully aneuploids, such as hostas with a DNA ploidy of L1‐L2‐L3 = 2.5‐2.5‐2.5 and 3.7‐3.7‐3.7, and even in aneuploid periclinal chimeras, such as L1‐L2‐L3 = 2.5‐2‐2 and 3.8‐2‐2. The polyploidy of L1, irrespective of the ploidy of L2 and L3, is found to mainly determine the thickness of leaves. Also the higher the ploidy of L1, the wider and more intense in color is the leaf margin. The measurements of Hosta cultivars and their lineages of sports show that chromosome losses or gains are an important source of new cultivars. The complexity of chromosomal distribution in lineages of several Hosta cultivars is discussed.     

Temperature effects on egg development of the rosy apple aphid and forecasting of egg hatch

The development of Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) winter eggs was studied at six different constant temperatures ranging from 7.5 to 16.5 °C in order to improve the basis for phenological forecasts in early spring. The mortality was generally low at temperatures below 13.5 °C but increased considerably at 16.5 °C. The effect of temperature on development rates could be described with linear regression within the temperature range under study. The lower temperature threshold for development was estimated to be 4.0 °C and the thermal constant 140 day‐degrees. A time‐varying distributed delay approach was used to establish a temperature driven phenology model for winter egg hatch of D. plantaginea considering the intrinsic variability in development time. The model parameters such as temperature‐dependent development times and corresponding variances were quantified based on the experimental data. When compared with independent observations on egg hatch under semifield conditions, the model gave satisfactory validation results. It can be used as forecasting tool for the optimal timing of monitoring and control measures for D. plantaginea in early spring.     

Endophytic bacterium,Bacillus amyloliquefaciens,enhances ornamental hosta resistance to diseases and insect pests

A total of 84 bacterial endophytes were isolated from seeds of 6 cultivars of ornamental hostas, and they were identified to 5 species based on morphological characteristics and 16S rDNA sequence analysis. Among them, the strain ‘Blu-v2’, which was isolated from the seeds of cultivar ‘Blue Umbrella’ and identified to be Bacillus amyloliquefaciens, showed highest antifungal activity and capacity to deter feeding by Fall armyworms (Spodoptera fruigiperda). Lipopeptides in cultures of Blu-v2 were determined using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and its antifungal activities were verified. However, the lipopeptide preparation did not show toxicity to larvae of Fall armyworms. In a greenhouse experiment, Blu-v2 was inoculated into small plantlets of hosta (cultivar ‘Rainforest Sunrise’). The leaves of plants with bacteria (endophyte-infected?=?E+) and without bacteria (endophyte-free?=?E?) were used in seven-day feeding experiments employing fourth-instar larvae of Fall armyworms. We found that there was a significant decrease in the weights of larvae fed with E+ compared to E? plants; and the mortality rate of larvae fed with E? leaves was lower (3.33%) compared to that of larvae fed with E+ leaves (30%). Based on our studies, we suggest that endophytic B. amyloliquefaciens strain Blu-v2 has potential value as a biocontrol agent to reduce damage from fungal diseases and insect pests of hosta cultivars.     

Genome Size and Pollen Viability as Taxonomic Criteria: Application to the Genus Hosta

Abstract: Genome size (C values) and pollen viability staining were applied as new criteria to investigate the taxonomy of the genus Hosta Tratt. (Hostaceae). Nearly all species of the genus Hosta have the same basic chromosome number (2n = 2x = 60). However, the nuclear DNA contents, as measured by flow cytometry with propidium iodide, could be demonstrated to range between 17.2 to 26.6 pg. This implies that the largest genome contains roughly 10¹⁰ more base pairs than the smallest. Therefore, nuclear DNA content is a very relevant taxonomic trait that can be measured simply by flow cytometry. In addition, differences in overall DNA composition were demonstrated by comparing to DAPI fluorescence. In general, genome size data confirmed the division into three subgenera. The geographical distribution of genome sizes indicates the migration pattern of Hosta throughout East Asia. The species belonging to the mainly Korean subgenus Bryocles, with a low nuclear DNA content (17.2 - 19.3 pg), can now largely be distinguished from the mainly Japanese species of the subgenus Giboshi (21.3 - 26.5 pg). The exception is H. longissima, that with only 19.6 pg provides a nice example of a decrease in DNA content. On the mainland, as well as on Honshu, species with increased and decreased DNA content have evolved independently. The usefulness of pollen viability to detect hybrids in Hosta was demonstrated in a large series of artificial crosses between bona fide species. Consequently, pollen viability was measured in all available Hosta described as species. Several had low pollen viability and were concluded to be hybrids. Morphology and DNA content confirmed this in most cases. The resulting 23 species approximate the number of Hosta species that follows from the combined studies by Fujita (1976¹⁸) on the Japanese species and Chung (1991 a¹¹) on the Korean species.     

Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

The relative importance of architecture and resource competition in allocation to pollen and ovule number within inflorescences of Hosta ventricosa varies with the resource pools

Background and Aims

Allocation of resources to floral traits often declines distally within inflorescences in flowering plants. Architecture and resource competition have been proposed as underlying mechanisms. The aim of the present study is to assess the relative importance of resource competition and architectural effects in pollen and ovule production on racemes of Hosta ventricosa, an apomictic perennial herb.

Methods

Combinations of two defoliation treatments (intact and defoliated) and two fruit-set treatments (no-fruit and fruit) were created, and the roles of architecture and resource competition at each resource level were assessed.

Key Results

Pollen and ovule number per flower increased after defoliation, but pollen to ovule ratio per flower did not change. Pollen, ovules and the pollen to ovule ratio per flower declined distally on racemes at each resource level. In the intact treatment, fruit development of early flowers did not affect either pollen or ovule number of late flowers. In the defoliated treatment, fruit development of early flowers reduced both pollen and ovule numbers of late flowers due to over-compensation caused by defoliation. Late flowers on defoliated fruit racemes produced less pollen than intact fruit racemes but the same number of ovules; therefore, the reduction in pollen number was not caused by over-compensation. In addition, the fruit-set rate of early flowers during flowering was higher in intact racemes than in defoliated racemes.

Conclusions

In flowering plants, the relative importance of architecture and resource competition in allocation to pollen and ovules may vary with the resource pools or the overall resource availability of maternal plants.     

Floral sex allocation and reproductive success within inflorescences of Hosta ventricosa,a pseudogamous apomict

Aims Within inflorescences of sexually reproducing hermaphrodites, the production of ovules, fruits and seeds commonly declines from basal (early-opening) to distal (late-opening) flowers, while pollen production remains constant or only changes slightly, with the result that distal (late-opening) flowers become functionally male. However, few empirical studies have specifically examined whether or not changes in allocation to pollen production actually lead to changes in the number of seeds sired, a more direct measure of male fitness. In pseudogamous apomicts, fitness depends on the number of seeds produced; thus, a contrasting pattern of variation in the pollen-to-ovule (P/O) ratio within inflorescences might be expected.Methods We investigated floral sex allocation and reproductive success within racemes of Hosta ventricosa, a pseudogamous apomictic hermaphrodite possessing flowers that open acropetally. We quantified variations in pollen number, ovule number, the P/O ratio and fruit and seed production, from 2007 to 2011, among flowers within racemes of four populations of H. ventricosa in southwest China. Ecological causes for fruit and seed production were evaluated by observing patterns of pollen deposition, flower removal and supplemental pollination.Important findings Pollen number, ovule number and the P/O ratio declined from basal-to-distal positions in all sampled populations (years). Fruit and seed production decreased distally in most populations (years). Low fruit and seed set of distal flowers was not due to pollen limitation because pollen deposition never declined distally and the low fruit and seed set of distal flowers remained even after supplementary pollination was provided. The flower-removal experiment indicated that inter-fruit competition for resources among flowers was common. The low P/O ratio of distal flowers in H. ventricosa might be favored because they were unable to obtain fitness by donating pollen and siring seeds on other plants. Our study may help to understand the adaptive significance of sex allocation among flowers within inflorescences of sexually reproducing hermaphrodites.     

The effect of ant attendance on the success of rosy apple aphid populations, natural enemy abundance and apple damage in orchards

1 The rosy apple aphid, Dysaphis plantaginea, is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention. 2 An ant exclusion study was conducted in two distant orchards within the U.K. At both sites, ants were excluded from a subset of D. plantaginea infested trees at the beginning of the season and populations were monitored. The number of natural enemies observed on trees was also recorded and, before harvest, the percentage of apples damaged by D. plantaginea calculated. 3 Overall, the exclusion of ants reduced the growth and eventual size of D. plantaginea populations. On trees accessed by ants, greater numbers of natural enemies were recorded, presumably because aphid populations were often greater on such trees. However, this increased natural enemy presence was diluted by the larger aphid populations such that individual aphids on ant‐attended trees were subjected to a lower natural enemy pressure compared with those on ant‐excluded trees. 4 At harvest, apple trees that had been accessed by ants bore a greater proportion of apples damaged by D. plantaginea. There were also differences in cultivar susceptibility to D. plantaginea damage. 5 The present study highlights the importance of the ant–D. plantaginea relationship and it ia suggested that ant manipulation, whether physically or by semiochemicals that disrupt the relationship, should be considered as a more prominent component in the development of future integrated pest management strategies.