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.     

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.     

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.     

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 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.     

Clonal and fine-scale genetic structure in populations of a restricted Korean endemic, Hosta jonesii (Liliaceae) and the implications for conservation

BACKGROUND AND AIMS: In plant populations the magnitude of spatial genetic structure of apparent individuals (including clonal ramets) can be different from that of sexual individuals (genets). Thus, distinguishing the effects of clonal versus sexual individuals in population genetic analyses could provide important insights for evolutionary biology and conservation. To investigate the effects of clonal spread on the fine-scale spatial genetic structure within plant populations, Hosta jonesii (Liliaceae), an endemic species to Korea, was chosen as a study species. METHODS: Using allozymes as genetic markers, spatial autocorrelation analysis of ramets and of genets was conducted to quantify the spatial scale of clonal spread and genotype distribution in two populations of H. jonesii. KEY RESULTS: Join-count statistics revealed that most clones are significantly aggregated at < 3-m interplant distance. Spatial autocorrelation analysis of all individuals resulted in significantly higher Moran's I values at 0-3-m interplant distance than analyses of population samples in which clones were excluded. However, significant fine-scale genetic structure was still observed when clones were excluded. CONCLUSIONS: These results suggest that clones enhance the magnitude of spatial autocorrelation due to localized clonal spread. The significant fine-scale genetic structure detected in samples excluding clones is consistent with the biological and ecological traits exhibited by H. jonesii including bee pollination and limited seed dispersal. For conservation purposes, genetic diversity would be maximized in local populations of H. jonesii by collecting or preserving individuals that are spaced at least 5 m apart.     

不同遮荫水平下4个玉簪品种的生长性状分析

研究了4 个玉簪品种(Hosta ‘Golden Edger’, H.‘Antioch’, H.sieboldiana ‘Elegans', H.plantagenea‘Aphrodite')在全日照的50%、30%和5%条件下的生长性状, 结果表明, 4 个玉簪品种的生长性状均受光照强度的影响, 随遮荫程度的加深, 所有供试品种的各生物量增量均表现下降, H.‘GoldenEdger'和H.plantagenea ‘Aphrodite'对光照较H.‘Antioch'和H.sieboldiana ‘Elegans'敏感, 前二者的适合生长光强为全光照的50%以上, 后两者适合生长的光强为全光照的30%~50%;光强对所有供试品种的单株总叶面积和株高均没有显著影响;各品种比叶重随光强减弱而下降;50%以上遮荫不利于芽及花序的产生。遮荫还改变各品种器官间的生物量分配比例, 50%以上遮荫使根生物量比例减少, 叶片生物量增加;随着遮荫程度的加深, 所有供试品种的各器官干重的总体减少程度大于鲜重。     

Molecular-genetic characterisation of a new nematode resistance gene in wheat

Bread wheat lines introgressed with Aegilops ventricosa chromosomes were evaluated for their resistance to the Australian cereal cyst nematode (CCN, Heterodera avenae) pathotype Ha13. Higher levels of resistance relative to the phenotype of the Cre1 CCN resistance gene in wheat were found in the donor Ae. ventricosa parental lines and chromosome-5N^v substitution or addition lines. The newly identified resistance to pathotype Ha13 on chromosome 5N^v, designated, Cre6, was shown to be independent of the Ae. ventricosa-derived Cre2 gene, effective against several European pathotypes. Another Ae. ventricosa derived gene, Cre5, showed partial resistance to pathotype Ha13. Inhibition of Ha13 female nematode reproduction was ranked in the order Cre6 >Cre1 >CreF≥Cre5. Cre6 was inherited as a single dominant locus. Gene sequences encoding nucleotide-binding sites and leucine-rich repeats (NBS-LRR) from the Cre3 CCN-pathotype Ha13 resistance locus were used as probes to isolate related sequences from one of the donor Ae. ventricosa parents. Related sequences from Ae. ventricosa (71–73% similarity at the amino-acid level to the Cre3-derived sequences) of chromosome 5N^v origin were identified and served as diagnostic molecular markers for the presence of 5N^v. CCN-susceptible plants, found as variants in some of the purported chromosome 5N^v lines, were also found to be missing the diagnostic 5N^v RFLP markers assayed by the NBS-LRR probe. An alloplasmic chromosome-5N^v addition line with Ae. ventricosa cytoplasm in the wheat cultivar, Moisson, background was particularly variable, with 43% CCN-susceptible plants and a corresponding loss of the diagnostic chromosome-5 molecular markers. Received: 26 June 2000 / Accepted: 15 July 2000