Mixed Reproductive Mode Research Articles

Two new species of Strandesia Stuhlmann, 1888 (Crustacea: Ostracoda) from Thailand, with first record of a male S. martensi Savatenalinton, 2015

Two new species of Strandesia Stuhlmann, 1888 are described from the northeastern part of Thailand: S. karanovicae sp. nov. and S. amnatcharoenensis sp. nov. Strandesia karanovicae is characterized by a tumid carapace in dorsal view, a small anterior overlap, the absence of a dorso-subapical seta on the first segment of the antennule (A1), a large aesthetasc Y on the antenna, an α seta shape with a needle-like tip and a large β seta on the mandibular palp (Md-palp), serrated bristles on the maxilla, a long h1 seta on the second thoracopod (T2) and a slender caudal ramus (CR). Strandesia amnatcharoenensis has a small compressed posterior part of the right valves (RV) which makes it closely related to S. pholpunthini Savatenalinton, 2015. The new species can be distinguished primarily by a considerably small anterior overlap of the left valve over the right valve (RV), a postero-ventral flange of the RV, a remarkably large claw Ga of the CR and the chaetotaxy of the limbs, especially A1, Md-palp and T2. In addition, in the present study, the sexual population of S. martensi Savatenalinton, 2015 is recorded for the first time, and thus the first description of the male is provided here. Moreover, the morphological examination of both males and females revealed differences between asexual and sexual females and also points to the fact that S. martensi is a mixed reproduction species. This is the first record of the mixed reproductive mode in the genus Strandesia or even in the Cypricercinae.

The Impatiens Downy Mildew Epidemic in the United States Is Caused by New, Introgressed Lineages of Plasmopara destructor with Prominent Genotypic Diversity and High Evolutionary Potential.

Impatiens downy mildew (IDM) caused by Plasmopara destructor is currently the primary constraint on the production and use of impatiens (Impatiens walleriana) as bedding plants worldwide. Downy mildew has been documented since the 1880s from wild-grown Impatiens spp. but epidemic outbreaks of the disease affecting the commercially grown, ornamental I. walleriana were only reported for the first time in 2003 in the United Kingdom and in 2004 in the United States. Here, we assess the genetic diversity, level of differentiation, and population structure from 623 samples associated with current and preepidemic IDM outbreaks, by genotyping the samples with simple sequence repeat markers. P. destructor population structure following the emergence of IDM in the United States is subdivided into four genetic lineages characterized by high genetic diversity, mixed reproduction mode, inbreeding, and an excess of heterozygosity. P. destructor genotypes are significantly differentiated from preepidemic IDM samples from hosts other than I. walleriana but no geographical or temporal subdivision is evident. P. destructor samples from different Impatiens spp. show significant but very low levels of differentiation in the analysis of molecular variance test that did not hold in discriminant analysis of principal components analyses. The same was observed between samples of P. destructor and P. velutina recovered from I. walleriana. The finding of shared genotypes in samples from different countries and lack of differentiation among U.S. and Costa Rican samples indicate the occurrence of international movement of the pathogen. Our study provides the first high-resolution analysis of the diversity of P. destructor populations and the IDM epidemic that may be instrumental for disease management and breeding efforts.

SSR variability of stem rust pathogen on spring bread wheat in Russia.

Wheat stem rust caused by Puccinia graminis f. sp. tritici Erikss. & E. Henning (Pgt), which used to be a harmful disease of winter wheats in the southern part of Russia, has been largely affecting the yield of spring bread wheat in the territories of temperate climate zone since 2009. A total of 222 Pgt isolates were obtained from samples of susceptible cultivars of spring bread wheat in Central and Volga regions, and Omsk and Novosibirsk provinces in 2019. Genotyping of the isolates was carried out at 16 SSR loci. Number of alleles, proportion of heterozygotes and deviation from Hardy-Weinberg equilibrium were determined at each SSR locus. Based on genetic variability of SSR genotypes, it was shown that the Pgt population is subdivided into two large clusters in the territory of Russian temperate climate zone: "European" population (the Central region) and "Asian" one (the Volga region and two main wheat provinces of Western Siberia). Both the Pgt populations are characterized by a mixed mode of reproduction (sexual and clonal), but different sources of inoculum seem to shape a genotype structure within them. A group of Pgt genotypes with high variability, the inbreeding coefficient closed to zero and low observed heterozygosity was revealed among samples from Omsk. Moreover, two singular SSR genotypes identified among the Asian samples of Pgt isolates should attract a special attention in monitoring of stem rust in order to disclose unexpected rapid changes of the pathogen in the corresponding regions and to prevent the disease outbreak.

Genomic diversity and genetic variation of Leishmania panamensis within its endemic range.

Species belonging to the Leishmania (Viannia) subgenus are important causative agents of cutaneous and mucocutaneous leishmaniasis in Central and South America. These parasites possess several distinctive biological features that are influenced by their genetics, population structure, and genome instability. To date, several studies have revealed varying degrees of genetic diversity within Leishmania species. Particularly, in species of the L. (Viannia) subgenus, a generalized high intraspecific genetic diversity has been reported, although, conflicting conclusions have been drawn using different molecular techniques. Despite being the most common Leishmania species circulating in Panama and Colombia, few studies have analyzed clinical samples of Leishmania panamensis using whole-genome sequencing, and their restricted number of samples has limited the information they can provide to understand the population structure of L. panamensis. Here, we used next generation sequencing (NGS) to explore the genetic diversity of L. panamensis within its endemic range, analyzing data from 43 isolates of Colombian and Panamanian origin. Our results show the occurrence of three well-defined geographically correlated groups, and suggests the possible occurrence of additional phylogeographic groups. Furthermore, these results support the existence of a mixed mode of reproduction in L. panamensis, with varying frequencies of events of genetic recombination occurring primarily within subpopulations of closely related strains. This study offers important insights into the population genetics and reproduction mode of L. panamensis, paving the way to better understand their population structure and the emergence and maintenance of key eco-epidemiological traits.

Biological flora of Britain and Ireland:Neottia nidus‐avis

AbstractThis account provides information on all aspects of the biology ofNeottia nidus‐avis(L.) Rich. (Bird's‐nest Orchid) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of Britain and Ireland: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, reproductive characteristics, herbivory, history and conservation.Neottia nidus‐avisis a native mycoheterotrophic orchid; it is found most frequently in the deep humus of densely shaded beech woodlands, on limestone or chalky soils in the British Isles. The species extends throughout temperate Eurasia.Neottia nidus‐avisis a perennial, mostly monocarpic herb with mixed mode of reproduction and many adaptations to autogamy. The perennating organ is a short rhizome; vegetative reproduction by rhizome branching or root‐sprouting is rather infrequent. Because of its achlorophyllous nature,N. nidus‐avisis entirely dependent on its mycorrhizal basidiomycetes from the family Sebacinaceae for nutrition.Plastid genome ofN. nidus‐avishas been reduced as a result of the relaxation of functional constraints on photosynthesis as in other mycoheterotrophic plants. Despite this, the plant has retained all enzymes to produce chlorophyll as well as some photoprotective metabolites, such as zeaxanthin and tocopherol, whose function in the mycoheterotrophic plant remains unresolved.The species flowers from May to June, depending on latitude and altitude. The flowers emit a sweet scent and produce little nectar. They may be pollinated by flies, crawling thrips and ants but self‐pollination is presumed to be the main mode of reproduction. Between 75% and 97% of open flowers set fruits.Neottia nidus‐avisis classified asVulnerablein Great Britain. The species is scattered throughout much of the British Isles, but it is very scarce except in southern England, where it is locally abundant. The main threats are deforestation, changes in woodland management and coniferization.

GENETIC ANALYSIS OF QUALITATIVE AND QUANTITATIVE TRAITS AMONG PROGENIES OF ENSET CLONES ORIGINATED FROM SOUTHERN ETHIOPIA

<p>The present cultivated enset (<em>Ensete ventricosum</em>) clonal landraces in Ethiopia originated from few wild progenitors. However, enset has a mixed mode of reproduction in which, the wild enset reproduces sexually through seeds, while cultivated enset is generally propagated vegetatively. The objectives of this study were to determine the genetic structure of enset cultivars through genetic analysis of qualitative morphological traits and estimate their genetic variability by evaluating the quantitative agronomic traits data generated from progenies of cultivated and wild enset genotypes. Hence, seeds collected from six cultivated and four wild enset genotypes were used for this study. Data on four qualitative and six quantitative morphological traits were recorded from the progenies of the 10 enset genotypes. Progenies of seven enset genotypes segregated in a 3:1 segregation ratio while progenies of the remaining genotypes segregated differently for the qualitative traits considered. With regard to the quantitative traits, the progenies of the 10 enset genotypes differed significantly for five of the six traits except pseudostem length. The cultivated clones, in general performed better than that of the wild types. Moderate heritability (h2b) estimates and high genetic advances were obtained for leaf length (0.38, 62.0%), pseudostem circumference (0.35, 78.5%), and plant height (0.30, 19.1%) indicating selection for these traits indirectly improves economic yield of enset clones. This study demonstrated the possibility of creating genetic variation through selfing the existing enset genotypes for traits of interest and making improvements either through selection or crossing the elite types to develop novel enset cultivars.</p>

Genotyping by sequencing suggests overwintering of Peronospora destructor in southwestern Québec, Canada.

Several Peronospora species are carried by wind over short and long distances, from warmer climates where they survive on living plants to cooler climates. In eastern Canada, this annual flow of sporangia was thought to be the main source of Peronospora destructor responsible for onion downy mildew. However, the results of a recent study showed that the increasing frequency of onion downy mildew epidemics in eastern Canada is associated with warmer autumns, milder winters, and previous year disease severity, suggesting overwintering of the inoculum in an area where the pathogen is not known to be endogenous. In this study, genotyping by sequencing was used to investigate the population structure of P. destructor at the landscape scale. The study focused on a particular region of southwestern Québec—Les Jardins de Napierville—to determine if the populations were clonal and regionally differentiated. The data were characterized by a high level of linkage disequilibrium, characteristic of clonal organisms. Consequently, the null hypothesis of random mating was rejected when tested on predefined or nonpredefined populations, indicating that linkage disequilibrium was not a function of population structure and suggesting a mixed reproduction mode. Discriminant analysis of principal components performed with predefined population assignment allowed grouping P. destructor isolates by geographical regions, while analysis of molecular variance confirmed that this genetic differentiation was significant at the regional level. Without using a priori population assignment, isolates were clustered into four genetic clusters. These results represent a baseline estimate of the genetic diversity and population structure of P. destructor.

On computing relative effective population size estimates and parameters from an equilibrium cycle of hermaphrodite frequency fluctuation due to mixed reproductive modes in filamentous fungi

Many filamentous ascomycete fungi reproduce primarily asexually, with only occasional sexual generations. This can lead to a departure from the 1:1 mating type ratio that is expected in obligate sexual populations. The relaxed selection on sexual traits also can lead to a decrease in the frequency of female fertile strains in field populations, while male fertility does not similarly decrease since male gametes also can serve as asexual spores. Both changes ultimately impact the strength of genetic drift in populations. The frequency of female sterility likely increases with the time since the last generation of sexual reproduction, such that it can be used to estimate the relative frequency of sexual reproduction. Here I provide additional details relevant to Leslie and Klein’s (1996) model of mixed sexual reproduction and vegetative propagation as related to the frequency of female sterility. This includes new or modified equations that allow for simpler calculations of i) two estimates of relative Ne, ii) the expected range of hermaphrodite frequencies during the cycles of mixed reproduction, and iii) the relative frequency of sex. These equations also are included in spreadsheet templates into which researchers can directly enter frequencies computed from their population data to estimate these parameters for their own populations. These resources will make the results of Leslie and Klein (1996) more accessible and should increase the use of this model in evaluating the frequency of sexual reproduction of filamentous fungi.

Temporal diversification and no geographic population structure in the most abundant European ectomycorrhizal fungus Russula ochroleuca

Abstract Although Russula ochroleuca is a common ectomycorrhizal (ECM) species in European forests, its reproduction mode, dispersal range, and population structure remains unknown. Altogether, 462 fruit bodies from three spruce forests (two 15 km apart, one 230 km distant from the first two) were analysed using AFLP markers. A mixed mode of reproduction, with several large genets accompanied by a majority of single fruit body genets, was found. Low level of inbreeding (Fis = 0.0021–0.0072), low level of genetic differentiation among subpopulations (PhiPT = 0.037–0.190) and negligible isolation by distance (r = 0.033, P = 0.005) indicates effective spore dispersal and a high level of outcrossing across the sampled area. Finally, we discovered temporal diversification within this species, as evidenced by genetic differentiation between early (August) and late (September) fruiting genotypes.

Dependence of egg hatching on Wolbachia density in a parthenogenetic weevil revealed by antibiotic treatment

AbstractNaupactini is a tribe of Neotropical broad‐nosed weevils highly diverse in South America. This group includes several parthenogenetic species, some of them harmful for agriculture and invasive around the world. Although some hypotheses based on polyploidy and hybridization have been proposed to explain the origin of parthenogenesis in weevils, the infection with the bacterium Wolbachia pipientis may be involved in the origin of parthenogenetic reproduction of some species. In this contribution, we studied the role of Wolbachia in the reproductive biology of Pantomorus postfasciatus Hustache (Coleoptera: Curculionidae) through a curing experiment using tetracycline. This weevil has a mixed mode of reproduction including sexual and parthenogenetic populations. Exposure to an antibiotic did not affect fecundity, but did reduce egg hatching in comparison with untreated individuals. Consequently, we inferred that Wolbachia most probably takes part in the reproduction of P. postfasciatus, either by exerting nutritive functions in oogenesis necessary for egg hatching, or by induction of thelytokous parthenogenesis. Although infection was not totally cured, Wolbachia load was significantly lower in treated than in control females. Thereby, we hypothesize that a minimum threshold density of Wolbachia is required for weevil reproduction. We conclude that all analyses support a role of Wolbachia in P. postfasciatus reproduction.

Approximating the Coalescent Under Facultative Sex.

Genome studies of facultative sexual species, which can either reproduce sexually or asexually, are providing insight into the evolutionary consequences of mixed reproductive modes. It is currently unclear to what extent the evolutionary history of facultative sexuals' genomes can be approximated by the standard coalescent, and if a coalescent effective population size Ne exists. Here, I determine if and when these approximations can be made. When sex is frequent (occurring at a frequency much greater than 1/N per reproduction per generation, for N the actual population size), the underlying genealogy can be approximated by the standard coalescent, with a coalescent Ne≈N. When sex is very rare (at frequency much lower than 1/N), approximations for the pairwise coalescent time can be obtained, which is strongly influenced by the frequencies of sex and mitotic gene conversion, rather than N. However, these terms do not translate into a coalescent Ne. These results are used to discuss the best sampling strategies for investigating the evolutionary history of facultative sexual species.

Prevention and Detection of Fungicide Resistance Development in Rhizoctonia zeae from Soybean and Corn in Nebraska

The goal of this research was to advance the foundational knowledge required to quantify and mitigate fungicide resistance in Rhizoctonia zeae, the seedling disease pathogen of soybean and corn. In vitro sensitivity to azoxystrobin, fludioxonil, sedaxane, and/or prothioconazole was determined for 91 R. zeae isolates obtained mostly from soybean and corn fields in Nebraska. Isolates were sensitive to fludioxonil, sedaxane, and prothioconazole (EC50 < 3 µg/ml) and had a positively skewed EC50 distribution. Isolates were not sensitive to azoxystrobin in vitro (EC50 > 100 µg/ml) or in planta. Application of azoxystrobin did not significantly decrease disease severity or improve total dry weight of the soybean plants (P > 0.05). The risk of resistance development in R. zeae was estimated by characterizing its population structure. Eighty-one R. zeae isolates were genotyped using six microsatellite markers. Results showed that the population has a mixed mode of reproduction and is structured according to geographic region, suggesting limited dispersal. These population characteristics suggest that R. zeae has an intermediate risk of resistance development. Overall, this research established the current status of fungicide sensitivity in R. zeae in Nebraska and estimated its risk of resistance development, which can inform fungicide resistance management for R. zeae.

Reproductive ecology of Saxifraga florulenta, a monocarpic perennial paleo-endemic of the Alps

Saxifraga florulenta is a monocarpic species endemic to SW Alps, whose reproductive biology is still unknown. Its knowledge may provide useful information on how the species may face the global warming. In this study, we investigated the plant–pollinator interactions and the mating system of the plant. We described the phenology of the inflorescences, we evaluated the type of pollinators, we verified self and cross-pollination and lastly we quantified the reproductive success of the plants. In spite of the low visitation rate of pollinators, S. florulenta shows high fruit set and seed set. The plant exhibits a prolonged flowering period and has a definite inflorescence, characterized by a sequential blooming bearing both female- or male-phase flowers at the same time; in addition, flowers show a delayed maturation and movement of stamens. These floral and inflorescence traits lead to a mixed reproduction mode which guarantees reproductive success by adopting the “best of two worlds” strategy. The species maximizes its resource investment by having inflorescence size and number of flowers directly related to plant size, whilst fruit and seed set as well as seeds per flower did not show any statistically significant relationship with plant size.

Shifts in coral clonality along a gradient of disturbance: insights on reproduction and dispersal of Pocillopora acuta

Pocillopora acuta, formerly synonymized with P. damicornis, is an ecologically important reef-building coral that exhibits mixed reproductive modes, geographic variation in clonality, and conflicting reports of population genetic structure. Using 16 polymorphic microsatellite loci, this study examined clonality, genetic differentiation, and connectivity of genetically identified P. acuta (n = 428) in the Bolinao–Anda Reef Complex (BARC), Philippines, characterized by varying levels of wave exposure. Estimates of clonal richness indicate that the populations are largely derived from asexual reproduction, more likely via dispersal of ameiotic larvae. Clonal richness, population density, and mean colony size vary with wave exposure, suggesting the potential influence of local-scale disturbance on clonality, reproductive mode, and population structure. Populations in low-energy environments were characterized by greater colony density, larger colonies, and a greater proportion of clones compared to high-energy environments. Despite evidence for realized clonal dispersal of P. acuta extending up to 22 km, significant genetic differentiation among BARC populations reveals restricted gene flow at small spatial scales. Moreover, genetic differentiation is more pronounced when considering the spatial distribution of clones (FST including clones = 0.059; FST excluding clones = 0.028), suggesting that (1) asexually produced propagules are likely retained locally and across-site settlement is not as common; and (2) sexually derived propagules may have broader scales of dispersal. This study reexamines the population genetics of this often-problematic coral and underlines the importance of contextualizing site and species biology in designing or enhancing management towards the maintenance of functional genetic diversity and pathways of connectivity among populations.

Occurrence of apomictic conspecifics and ecological preferences rather than colonization history govern the geographic distribution of sexual Potentilla puberula.

The geographic distribution of sexual‐apomictic taxa (i.e., comprising individuals usually reproducing either sexually or asexually via seeds) is traditionally thought to be driven by their ecological preferences and colonization histories. Where sexuals and apomicts get into contact with each other, competitive and reproductive interactions can interfere with these factors, an aspect which hitherto received little attention in biogeographic studies. We disentangled and quantified the relative effects of the three factors on the distribution of tetraploid sexuals in Potentilla puberula in a latitudinal transect through the Eastern European Alps, in which they are codistributed with penta‐, hepta‐, and octoploid apomictic conspecifics. Effects were explored by means of binomial generalized linear regression models combining a single with a multiple predictor approach. Postglacial colonization history was inferred from population genetic variation (AFLPs and cpDNA) and quantified using a cost distance metric. The study was based on 235 populations, which were purely sexual, purely apomictic, or of mixed reproductive mode. The occurrence of apomicts explained most of the variation in the distribution of sexuals (31%). Specifically, the presence of sexual tetraploids was negatively related to the presence of each of the three apomictic cytotypes. Effects of ecological preferences were substantial too (7% and 12% of the total variation explained by ecological preferences alone, or jointly with apomicts’ occurrence, respectively). In contrast, colonization history had negligible effects on the occurrence of sexuals. Taken together, our results highlight the potentially high impact of reproductive interactions on the geographic distribution of sexual and apomictic conspecifics and that resultant mutual exclusion interrelates to ecological differentiation, a situation potentially promoting their local coexistence.

Genetic Structure of Rhizoctonia solani AG-2-2IIIB from Soybean in Illinois, Ohio, and Ontario

Rhizoctonia solani AG-2-2IIIB is an important seedling pathogen of soybean in North America and other soybean-growing regions around the world. There is no information regarding the population genetics of field populations of R. solani associated with soybean seedling disease. More specifically, information regarding genetic diversity, the mode of reproduction, and the evolutionary factors that shape different R. solani populations separated in time and space are lacking. We exploited genotyping by sequencing as a tool to assess the genetic structure of R. solani AG-2-2IIIB populations from Illinois, Ohio, and Ontario and investigate the reproductive mode of this subgroup. Our results revealed differences in genotypic diversity among three populations, with the Ontario population having greatest diversity. An overrepresentation of multilocus genotypes (MLGs) and a rejection of the null hypothesis of random mating in all three populations suggested clonality within each population. However, phylogenetic analysis revealed long terminal multifurcating branches for most members of the Ontario population, suggesting a mixed reproductive mode for this population. Analysis of molecular variance revealed low levels of population differentiation, and sharing of similar MLGs among populations highlights the role of genotype flow as an evolutionary force shaping population structure of this subgroup.

Genetic diversity evidence a mixed reproduction mode in Venturia oleaginea populations in Uruguay

Olive scab caused by Venturia oleaginea is one of the most important diseases of olive worldwide. The fungus infects young leaves and fruits by asexually produced conidia. The sexual stage and its importance in the epidemiology and genetics of the pathogen population is unknown. A collection of 52 fungal isolates was obtained from scabbed leaves collected in 16 orchards from three major regions in Uruguay. All isolates were identified as V. oleaginea by PCR with specific primers and sequence analysis of the TEF-1α gene region. Five colony morphotypes and different growing rates were observed on potato dextrose agar (PDA) medium. Universally primed polymerase chain reaction (UP-PCR) was successfully used for assessing the genetic diversity and population structure of the V. oleaginea isolates, whereas ISSR was unable to generate reproducible and polymorphic bands. Two populations genetically different were identified: [1] composed by 21 isolates mainly from Southern and South-Western regions; [2] composed by 31 isolates mainly from South-Eastern and Southern regions. Both populations showed a moderate gene diversity expressed as hNei = 0.163 and 0.212 for population [1] and [2], respectively. There was evidence of linkage disequilibrium in both populations, rejecting the null hypothesis of random mating as the predominant reproduction mode, a typical result of clonal populations. However, all isolates were genotypically different, an indirect evidence of recombination. We conclude that V. oleaginea populations in Uruguay present a mixed mode of reproduction, a characteristic of many pathogens that are difficult to control.

Population Structure of Colletotrichum tanaceti in Australian Pyrethrum Reveals High Evolutionary Potential.

Colletotrichum tanaceti, the causal agent of anthracnose, is an emerging pathogen of commercially grown pyrethrum (Tanacetum cinerariifolium) in Australia. A microsatellite marker library was developed to understand the spatio-genetic structure over three sampled years and across two regions where pyrethrum is cultivated in Australia. Results indicated that C. tanaceti was highly diverse with a mixed reproductive mode; comprising both sexual and clonal reproduction. Sexual reproduction of C. tanaceti was more prevalent in Tasmania than in Victoria. Little differentiation was observed among field populations likely due to isolation by colonization but most of the genetic variation was occurring within populations. C. tanaceti was likely to have had a long-distance gene and genotype flow among distant populations within a state and between states. Anthropogenic transmission of propagules and wind dispersal of ascospores are the most probable mechanisms of long-distance dispersal of C. tanaceti. Evaluation of putative population histories suggested that C. tanaceti most likely originated in Tasmania and expanded from an unidentified host onto pyrethrum. Victoria was later invaded by the Tasmanian population. With the mixed mode of reproduction and possible long-distance gene flow, C. tanaceti is likely to have a high evolutionary potential and thereby has ability to adapt to management practices in the future.

Observations of Simultaneous Sperm Release and Larval Planulation Suggest Reproductive Assurance in the Coral Pocillopora acuta

Despite being an extensively studied group of corals, the reproductive biology of the scleractinian genus Pocillopora remains a mystery. Pocillopora acuta has been proposed to exhibit a mixed reproductive mode, sexually producing gametes (sperm and eggs) and asexually brooding larvae simultaneously within a single colony. Here, we report observations of night-time spawning of sperm during the peak monthly larval release period. We offer a new hypothesis for the regulation of sexual and asexual reproduction in the species and posit that sexual reproduction may occur more often than previously suggested. However, the success of internal oocyte fertilization and subsequent zygote development is dependent on sperm making contact with a fertile colony. We hypothesize that asexual development of larvae occurs when sperm is absent, but more extensive genetic, genomic, and histological data are required to determine the pathway by which unfertilized oocytes may develop. We also propose that this mixed mode of reproduction is an adaptation to mating failure, common in sessile marine invertebrates. The reproductive assurance enjoyed by the species may therefore be the key to its ecological and evolutionary persistence.

Genetic Diversity and Differentiation in Phoma betae Populations on Table Beet in New York and Washington States.

Phoma betae is an important seedborne pathogen of table beet worldwide that is capable of causing foliar, root, and damping-off diseases. Ten microsatellite and mating type markers were developed to investigate the genetics of P. betae populations in table beet root crops in New York and in table beet seed crops in Washington, from where table beet seed is predominantly sourced. The markers were used to characterize 175 isolates comprising five P. betae populations (two from New York and three from Washington), and they were highly polymorphic with an allelic range of 4 to 33 and an average of 11.7 alleles per locus. All populations had high genotypic diversity (Simpson's complement index = 0.857 to 0.924) and moderate allelic diversity (Nei's unbiased gene diversity = 0.582 to 0.653). Greater differentiation observed between populations from the two states compared with populations within the same state suggested that an external inoculum source, such as windblown ascospores, may be homogenizing the populations. However, most genetic diversity (87%) was among individual isolates within populations (pairwise index of population differentiation = 0.127; P = 0.001), suggesting that local within-field inoculum source(s), such as infested field debris or infected weeds, may also be important in initiating disease outbreaks. Standardized index of association, proportion of compatible pairs of loci, and mating type ratio calculations showed evidence for a mixed reproduction mode in all populations. These findings could be useful in designing more effective management strategies for diseases caused by P. betae in table beet production.