Mating Type Distribution Research Articles

Global Genetic Diversity and Mating Type Distribution of Calonectria pauciramosa: An Important Wide-Host-Range Plant Pathogen.

The fungal pathogen, Calonectria pauciramosa, has caused serious diseases of many important plants worldwide. Understanding the genetic diversity and mating type distribution of this pathogen provides an essential step toward the development of disease control measures. In this study, we designed 15 polymorphic microsatellite markers by using genome sequences of two Ca. pauciramosa isolates having opposite mating type and from different countries. These markers were used to determine the genetic diversity of 145 isolates representing 13 different hosts (12 plant hosts residing in 12 genera, and soil) from 10 countries. In addition, mating type genes were amplified to investigate the reproduction mode of the pathogens in these populations by using mating type primers designed for Calonectria spp. Results revealed that a single dominant genotype, isolated from 11 plant genera residing in eight families, was present in seven countries across five continents. Only mating type MAT1-1 or MAT1-2 was amplified in each of the isolates, confirming that Ca. pauciramosa is heterothallic. Both mating types were detected in isolates from Eucalyptus in South Africa and Uruguay. The MAT1-2 phenotype was widely distributed in isolates from 12 different hosts (11 plant hosts and soil) collected in 10 countries. Overall, the results suggest that there has been substantial global movement of Ca. pauciramosa and that this has shaped its current population structure.

Morpho-molecular and mating-type locus diversity of Ustilaginoidea virens: an incitant of false smut of rice from Southern parts of India.

To characterize the geo-distinct isolates of Ustilaginoidea virens for morpho-molecular and mating-type locus diversity. Sixty-one isolates of U.virens collected from Southern India exhibited significant diversity in mycelial width (3·45-5·50µm), colony colour (yellow, pale yellow, and white), and growth pattern (thick leather mat, raised-fluffy, flat-fluffy, and raised). Field-borne chlamydospores of each isolate were significantly smaller in size (3·34-5·26µm2 ) compared to those formed on culture media (18·6-100·89µm2 ). The phylogenetic study based on internal transcribed sequences revealed two clusters; however, most isolates (n=54) were grouped in cluster-I, indicating common ancestral origin. We also identified 42 haplotypes; among them, Hap_3 has the highest number of isolates (n=19). Mating-type locus (MAT1) analysis revealed all sixty-one isolates as heterothallic, wherein 37 and 24 isolates belonging to MAT1-1-1 and MAT1-2-1 heterothallic mating types, respectively. The microsynteny analysis of MAT1 loci of one of the Indian strain (Uv-Gvt) along with Uv-8b (China) strain revealed synteny conservation at MAT1 locus, which is flanked by conserved genes SLA2 and a hypothetical protein in the upstream and APN2, COX12 and APC5 in the downstream of the locus. Morpho-molecular study revealed the significant diversity among geo-distinct isolates, and MAT1 loci analysis indicated the distribution of heterothallic mating types in south Indian paddy fields. And also, complete synteny conservation between Indian and Chinese strain was observed at the MAT1 locus. This is the first report describing the sexuality of Indian strains of the U.virens, which would help better understand the genetic diversity of the U.virens prevailing in Southern India and aid in developing resistant rice cultivars against this pathogen population.

Genetic Diversity and Mating Type Distribution of Pseudocercospora fijiensis on Banana in Uganda and Tanzania.

Black Sigatoka, caused by Pseudocercospora fijiensis, is a major foliar disease of banana and plantain worldwide. There are few available data regarding the genetic diversity and population structure of the pathogen in East Africa, which are needed to design effective and durable disease management strategies. We genotyped 319 single-spore isolates of P. fijiensis collected from seven regions in Uganda and Tanzania and five isolates from Nigeria using 16 simple sequence repeat markers and mating type-specific primers. Isolates from each country and region within the country were treated as populations and subpopulations, respectively. A total of 296 multilocus genotypes (MLGs) were recovered, representing a clonal fraction of 7%. Subpopulations had a moderate level of genetic diversity (Hexp = 0.12 to 0.31; mean, 0.29). Mating type distribution did not deviate from equilibrium (MAT1-1: MAT1-2, 1:1 ratio) in Uganda; however, in Tanzania the mating types were not in equilibrium (4:1 ratio). The index of association tests (IA and r̄d) showed that all populations were at linkage equilibrium (P > 0.05), thus supporting the hypothesis of random association of alleles. These findings are consistent with a pathogen that reproduces both clonally and sexually. Low and insignificant levels of population differentiation were detected, with 90% of the variation occurring among isolates within subpopulations. The high intrapopulation variation has implications in breeding for resistance to P. fijiensis because isolates differing in aggressiveness and virulence are likely to exist over small spatial scales. Diverse isolates will be required for resistance screening to ensure selection of banana cultivars with durable resistance to Sigatoka in East Africa.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Switching environments, synchronous sex, and the evolution of mating types

While facultative sex is common in sexually reproducing species, for reasons of tractability most mathematical models assume that such sex is asynchronous in the population. In this paper, we develop a model of switching environments to instead capture the effect of an entire population transitioning synchronously between sexual and asexual modes of reproduction. We use this model to investigate the evolution of the number of self-incompatible mating types in finite populations, which empirically can range from two to thousands. When environmental switching is fast, we recover the results of earlier studies that implicitly assumed populations were engaged in asynchronous sexual reproduction. However when the environment switches slowly, we see deviations from previous asynchronous theory, including a lower number of mating types at equilibrium and bimodality in the stationary distribution of mating types. We provide analytic approximations for both the fast and slow switching regimes, as well as a numerical scheme based on the Kolmogorov equations for the system to quickly evaluate the model dynamics at intermediate parameters. Our approach exploits properties of integer partitions in number theory. We also demonstrate how additional biological processes such as selective sweeps can be accounted for in this switching environment framework, showing that beneficial mutations can further erode mating type diversity in synchronous facultatively sexual populations.

Genetic variation and mating type distribution of Rhynchosporium commune in Turkey

Rhynchosporium commune is the causal agent of barley scald disease and is an important foliar disease of barley worldwide. During 2012, 2013, and 2014, Rhynchosporium commune single-spore isolates were collected from different parts of Turkey, and from those, 60 isolates were selected. The mating type distribution and prevalence of these selected isolates were determined. Twenty-one of the 60 single-spore isolates were found to be MAT1-1 type and 39 isolates were MAT1-2 type χ2 (1:1) types = 5.40 (P = 0.02). The mating type ratio showed that R. commune populations may have predominantly asexual reproduction in Turkey. To determine the genetic diversity of R. commune isolates, 5 single-spore isolates from different regions of Turkey were tested with 72 ISSR primers. Eleven primers were found to be polymorphic. UBC 826, UBC 861, UBC 886, UBC 887, UBC 890, UBC 848, UBC 884 and UBC 850 primers showed optimal band numbers and good band intensities. Sixty isolates were evaluated with these 8 ISSR primers. UBC826 and UBC886 primers amplified the largest numbers of bands. The genetic diversity of the isolates in the R. commune population in Turkey appeared to be low. There were no definite groupings of the mating type or geographical region. Turkey is one of the gene centers of barley and this study is the first one addressing the genetic variation and mating type distribution of R. commune in Turkey. The low genetic diversity and possible asexual reproduction observed in our study may contribute to the hypothesis that R. commune did not evolve in the origin of the barley plant.

Molecular-based assessment of diversity and population structure of Sporothrix spp. clinical isolates from Espírito Santo-Brazil.

Sporotrichosis is a subcutaneous mycosis caused by Sporothrix species that affects humans and animals. Little information on the genetic diversity and population structure of the pathogen is available for Brazil, which is needed to design effective strategies to tackle the advance of sporotrichosis in endemic areas. We assessed the genetic diversity and mating-type distribution of Sporothrix isolates recovered from human and feline cases of sporotrichosis in Espírito Santo-Brazil to better understand the population structure, epidemiology and diversification of this pathogen, as well as to explore the possible routes of transmission involved in the ongoing outbreaks. In all, 75 Sporothrix isolates were identified with phenotypic characteristics. Then, fungal DNA extraction was performed, and the species-specific PCR technique was applied, using markers directed to the calmodulin gene. The mating-type idiomorph of species was identified by PCR using primers targeting the MAT1-1 and MAT1-2 loci. Among the 75 Sporothrix isolates, 76% were confirmed as S brasiliensis and 24% as S schenckii sensu stricto. S brasiliensis was more prevalent in the metropolitan area and S schenckii s. str. in the mountainous region of the state. In both species, the presence of the two sexual idiomorphs was detected, suggesting that they are heterothallic species. Our data suggest that sporotrichosis takes on an epidemic-urban character involving Sbrasiliensis. This species in Espírito Santo is likely to originate from Rio de Janeiro, as most isolates harbour the same MAT 1-2 locus. We confirm that Sbrasiliensis has significantly broadened its area of occurrence, an essential feature of emerging pathogens.

Distribution and frequency of mating types of Rhynchosporium commune in central Alberta

Rhynchosporium commune, the cause of barley scald, is an important disease of barley in Canada. Multiple studies have indicated that cryptic sexual reproduction may occur between opposite mating types (MAT1-1 and MAT1-2). The occurrence of R. commune mating types in Canada has not been determined previously. Infected leaves from barley cultivars in seven commercial fields and three breeding nurseries in central Alberta were collected and subjected to multiplex PCR to assess the presence of scald mating types within the lesions. Mating types were determined in 410 scald lesions from 288 leaves. Over 10% of lesions contained both mating types, and 44% of leaves with more than one lesion analyzed were colonized by both mating types. The mating types significantly deviated from the 1:1 ratio that would have been expected with frequent sexual reproduction. MAT1-2 was more common in six of the ten locations and for the region as a whole. The presence of both mating types, often in close proximity to each other, suggests that the cryptic sexual stage could be present in Alberta if it does occur. The skewed mating type ratio does suggest, however, that asexual reproduction is predominant within the pathogen population.

Colonization by Tuber melanosporum and Tuber indicum affects the growth of Pinus armandii and phoD alkaline phosphatase encoding bacterial community in the rhizosphere

The synthesis of truffle ectomycorrhizae and the ecology of truffle-colonized seedlings in the early symbiotic stage are important for the successful truffle cultivation. In this study, two black truffle species, Tuber melanosporum and Tuber indicum, were selected to colonize Pinus armandii seedlings. 2, 4, 6 and 8 months after inoculation, the growth performance of the host and the rhizosphere soil properties were detected. The dynamic changes of two mating type genes in substrate were also monitored to assess the sexual distribution of truffles. Additionally, the variation of soil bacterial communities encoded by phoD alkaline phosphatase genes was investigated through next-generation sequencing. The results indicated that both T. melanosporum and T. indicum colonization promoted the growth of P. armandii seedlings to some extent, including improving their biomass, total root surface area, root superoxide dismutases and peroxidase activity. The organic matter and available phosphorus in rhizosphere soil were also significantly enhanced by two truffles’ colonization. The phoD-harboring bacterial community structure was altered by both truffles, and T. melanosporum decreased their diversity or richness on the 6th and 8th month after inoculation. Pseudomonas, Xanthomonas, and Sinorhizobium, a N2-fixer with phoD genes, were found more abundant in truffle-colonized treatments. The mating type distribution of the two truffles was uneven, with MAT1−1-1 gene occupying the majority. Overall, T. melanosporum and T. indicum colonization affected the micro-ecology of truffle symbionts during the early symbiotic stage. These results could give us a better understanding on the truffle-plant-soil-microbe interactions, which would be beneficial to the subsequent truffle cultivation.

First description of the sexual stage of Venturia effusa, causal agent of pecan scab

ABSTRACT Pecan scab, caused by Venturia effusa, is the most prevalent disease of pecan in the southeastern United States. Recent characterization of the mating type (MAT) distribution of V. effusa revealed that the MAT idiomorphs are in equilibrium at various spatial scales, indicative of regular sexual recombination. However, the occurrence of the sexual stage of V. effusa has never been observed, and the pathogen was previously considered to rely entirely on asexual reproduction. We were able to generate the sexual stage by pairing isolates of opposite mating types on oatmeal culture media. Cultures were incubated at 24 C for 2 mo to allow hyphae from isolates of each mating type to interact. Culture plates were then incubated at 4 C for 4 mo, after which immature pseudothecia were observed. Following exposure to a 12-h photoperiod for 2 wk at 24 C, asci and ascospores readily developed. Pseudothecium and ascospore production was optimal when incubated for 4 mo at 4 C. We utilized progeny from a cross of an albino isolate and wild-type (melanized) isolates to determine that recombination had occurred. Multilocus genotyping using 32 microsatellite markers confirmed that progeny were the result of recombination, which was further supported by segregation of mating types and culture pigmentation. Albino progeny were all confirmed to contain the same mutation in the polyketide synthase (PKS1) melanin biosynthesis gene as the albino parent. The results of this study demonstrate the heterothallic nature of V. effusa. The impact of determining the source of the overwintering ascostroma will aid in management decisions to reduce the primary inoculum in the disease cycle.

Mating strategy and mating type distribution in six global populations of the Eucalyptus foliar pathogen Teratosphaeria destructans

Teratosphaeria destructans is an aggressive fungal pathogen causing leaf and shoot blight on young Eucalyptus trees in plantations. The disease occurs across tropical and subtropical regions of South East Asia and has recently been found in South Africa. Asexual structures of the pathogen are produced on infected tissues, but sexual structures have never been observed. The aim of this study was to investigate the reproductive biology of T. destructans by characterising its mating type (MAT1) locus and investigating its potential for sexual recombination. We found that T. destructans has a heterothallic mating system, with either the MAT1-1-1 and MAT1-1-10 genes (MAT1-1 idiomorph) or the MAT1-2-1 and MAT1-2-12 genes (MAT1-2 idiomorph) present in a single individual. With a multiplex PCR assay, it was possible to distinguish the two MAT idiomorphs in several Teratosphaeria species and this approach was applied to six global populations of T. destructans. Although both mating types occurred in the South East Asian populations, a single mating type dominated each population. Isolates from the recent disease outbreak in South Africa comprised only a single mating type. Attempts to induce a sexual cycle in vitro using strains of opposite mating type were not successful. The uneven distribution of mating types in populations of T. destructans and the presence of only an asexual state on infected tissues suggests the absence of or at least a minor role for sexual reproduction where the pathogen occurs on non-native Eucalyptus in plantations.

Genomics Evolutionary History and Diagnostics of the Alternaria alternata Species Group Including Apple and Asian Pear Pathotypes.

The Alternaria section alternaria (Alternaria alternata species group) represents a diverse group of saprotroph, human allergens, and plant pathogens. Alternaria taxonomy has benefited from recent phylogenetic revision but the basis of differentiation between major phylogenetic clades within the group is not yet understood. Furthermore, genomic resources have been limited for the study of host-specific pathotypes. We report near complete genomes of the apple and Asian pear pathotypes as well as draft assemblies for a further 10 isolates representing Alternaria tenuissima and Alternaria arborescens lineages. These assemblies provide the first insights into differentiation of these taxa as well as allowing the description of effector and non-effector profiles of apple and pear conditionally dispensable chromosomes (CDCs). We define the phylogenetic relationship between the isolates sequenced in this study and a further 23 Alternaria spp. based on available genomes. We determine which of these genomes represent MAT1-1-1 or MAT1-2-1 idiomorphs and designate host-specific pathotypes. We show for the first time that the apple pathotype is polyphyletic, present in both the A. arborescens and A. tenuissima lineages. Furthermore, we profile a wider set of 89 isolates for both mating type idiomorphs and toxin gene markers. Mating-type distribution indicated that gene flow has occurred since the formation of A. tenuissima and A. arborescens lineages. We also developed primers designed to AMT14, a gene from the apple pathotype toxin gene cluster with homologs in all tested pathotypes. These primers allow identification and differentiation of apple, pear, and strawberry pathotypes, providing new tools for pathogen diagnostics.

Frequency and geographical distribution of genotypes and mating types of Cryptococcus neoformans and Cryptococcus gattii species complexes in Argentina

The aim of this work was to know the frequency and geographical distribution of genotypes and mating types of Cryptococcus neoformans and Cryptococcus gattii species complexes isolated from human infections in Argentina during the period from April 2009 to April 2011. A multicenter study was conducted, in which 372 isolates were obtained from 61 laboratories throughout the country. Of those, 98.8% of the isolates belonged to the C. neoformans species complex and 1.1% to the C. gattii species complex. Genotype VNI (MATα) was the most frequently isolated (n=326, 87.6%), followed by VNII (MATα) (n=22, 5.9%), the recently described VNII-VNIV (aADα) hybrid (n=14, 3.8%), VNIV (MATα) (n=4, 1.1%), VNIII (αADa) hybrid (n=1, 0.3%), and VNIII (αADα) hybrid (n=1, 0.3%). The Argentine Central region showed the greatest number of cases and genotype diversity. Interestingly, a relative high frequency was observed in genotype VNII (MATα) in the Cuyo, Northeast and Northwest regions and, also in VNII-VNIV (aADα) hybrids in the Northwest region. C. gattii species complex was isolated at a low rate; 3 VGI (MATα) and 1 VGII (MATα) isolates were obtained from the Northwest and Central regions. In conclusion, this study shows that genotype frequencies seem to vary among regions in Argentina and reveals a relatively high frequency of rare hybrids in the Northwest region. Further regional clinical and environmental studies may help to elucidate if those variations in frequencies are associated with the existence of regional ecological niches or any other regional factors.

Characterization of Natural Isolates of Bipolaris maydis Associated with Mating Types, Genetic Diversity, and Pathogenicity in Fujian Province, China.

Due to the natural destructiveness and persistence of the southern corn leaf blight (SCLB) fungus Bipolaris maydis (Nisikado et Miyake) Shoem, the characterization of B. maydis field isolates is essential to guide the rational distribution of resistant materials in corn-growing regions. In the present study, 102 field isolates collected from seven locations covering the entire region of Fujian Province, China, were assessed for mating type distribution, genetic diversity, and pathogenicity toward local sweet corn cultivars. Mating type detection via polymerase chain reaction indicated that 36.3 and 63.7% of isolates were MAT1-1 and MAT1-2, respectively; more than 80% of these isolates were confirmed using cross assays with known mating type isolates. Thirteen intersimple sequence repeat (ISSR) markers within and among two mating type populations revealed a high level of DNA polymorphism for all combined isolates and between MAT1-1 and MAT1-2 populations. The MAT1-2 population was more diverse based on DNA polymorphism than the MAT1-1 population. The value of GST was 0.0070, ranging from 0.0399 to 0.3044 based on analysis of combined isolates and individual regional populations, respectively, suggesting the presence of genetic differentiation in the two mating type populations from different locations. Pathogenicity assays revealed that both MAT1-1 and MAT1-2 populations were pathogenic to all 11 local sweet corn cultivars tested in this study. The potential of sexual reproduction, existence of genetic diversity in the two mating type populations, and pathogenicity suggest that B. maydis populations have independently clonally adapted under natural field conditions during corn cultivation.

Fusarium pseudograminearum as an emerging pathogen of crown rot of wheat in eastern China

Fusarium crown rot of wheat has been spreading in the Huanghuai wheat‐growing area in China since 2010, leading to a potential yield loss. To investigate the pathogens associated with this disease in Jiangsu and Shandong provinces in recent years, 617 Fusarium isolates were isolated from nine sites in these two provinces between 2014 and 2016. Of these isolates, 372 were identified as Fusarium pseudograminearum, and the remaining isolates were identified as F. asiaticum and F. graminearum, suggesting that F. pseudograminearum is becoming a predominant causative pathogen of crown rot of wheat in eastern China. Trichothecene gene detection and chemical analyses of trichothecenes indicated that the F. pseudograminearum isolates belonged to the 3‐ADON or 15‐ADON chemotype, and one isolate had the NIV genotype but produced no detectable NIV. 3‐ADON isolates were predominant in Jiangsu, whereas 15‐ADON isolates were prevalent in Shandong. The mating type of the F. pseudograminearum isolates were identified. MAT‐1 and MAT‐2 existed, but in most collections, particularly those in Jiangsu, the ratios of the two mating types deviated significantly from an expected 1:1 ratio. The reason for the occurrence of F. pseudograminearum is hypothesized, and the chemotype and mating type distribution of this species in these two provinces are analysed.

Distribution of mating type alleles in Iranian populations of Pyrenophora graminea, the causal agent of barley leaf stripe disease, using a multiplex PCR approach

Pyrenophora graminea is the main fungal species associated with barley leaf stripe disease worldwide. Even though a heterothallic mating strategy has been proven for P. graminea, this species is mainly known based on the asexual morph in nature and there is no available information on the prevalence of an active sexual cycle within the populations of this species in Iran as well as many other barley-producing countries. The feasibility of a cryptic sexual cycle within Iranian isolates of P. graminea was assessed through analyzing the distribution and frequency of the mating type alleles on micro-spatial and macro-geographical scales. A total number of 306 P. graminea isolates were obtained from 93 fields in 45 geographical regions across East Azerbaijan province during 2016–2017. A multiplex PCR assay was developed for simultaneous identification of P. graminea and screening of its mating type alleles using previously designed primer sets. Using the multiplex PCR assay, a 435-bp band was consistently amplified from all P. graminea isolates; while a 1300-bp fragment or a 1150-bp fragment was only amplified from the isolates harboring MAT-1 and MAT-2 alleles, respectively. The mating type identity of 164 isolates was determined as MAT-1 and 142 isolates as MAT-2. Results of the present study revealed a nearly equal distribution (1:1 ratio; X2=1.582) of mating type alleles within and between different populations of P. graminea. Results of the micro-spatial and macro-geographical distribution of mating types showed that both mating types were often present on almost all studied scales, including: within the same lesion of each leaf from a single barley plant, from the same field or different fields in the same region, and from different regions. Based on the results of the current study and referring to the earlier reports on the population structure of P. graminea, it is concluded that this pathogen undergoes regular cycles of sexual recombination in most of the examined regions.

Genomic characterization of mating type loci and mating type distribution in two apparently asexual plantation tree pathogens

The Eucalyptus stem canker pathogens Teratosphaeria gauchensis and T. zuluensis (Capnodiales, Teratosphaeriaceae) are found in many tropical regions of the world where their hosts are cultivated for plantation forestry. Population genetic analyses have suggested that some populations undergo recombination, even though their sexual states have never been observed. Against this background, the aim of this study was to characterize the mating type (MAT) locus of these species and thus to better understand the basis of their diversity. Known Mycosphaerellaceae MAT genes were used to identify and investigate the MAT locus in the T. gauchensis and T. zuluensis genomes. Both species were found to be heterothallic and primers were designed to amplify the opposite MAT idiomorphs as well as conserved regions within the MAT1‐1‐1 and MAT1‐2‐1 genes. Each Teratosphaeria MAT idiomorph was defined by either the MAT1‐1‐1 or the MAT1‐2‐1 gene, and an idiomorph‐specific hypothetical protein (MAT1‐1‐10 and MAT1‐2‐12). Populations of T. zuluensis from Asia and southern Africa were dominated by a single mating type, whereas the proportions of the different idiomorphs for T. gauchensis in South America and southern Africa were similar. There was no physical evidence of sexual reproduction for either species and it is argued that although recombination may be possible, it is unlikely to form an important part of their life cycles in diseased Eucalyptus plantations. Instead, continuous human‐mediated multiple introductions of these species have probably resulted in the current genetic structure of their populations, which holds risk for future disease outbreaks and interspecific hybridization.

She Loves Me, She Loves Me Not: On the Dualistic Asexual/Sexual Nature of Dermatophyte Fungi.

Dermatophytes are ascomycetous fungi whose sexuality is greatly influenced by their ecology. Sexual reproduction is ubiquitous among soil-related geophiles and some animal-associated zoophiles. In contrast, anthropophiles are generally present as a single mating type in the population and appear to reproduce asexually. In this article, the current knowledge on the sexuality of dermatophytes including reproduction modes, mating conditions, mating type distributions and the mating type (MAT) locus is presented in the context of revised taxonomy and discussed from an evolutionary perspective.

Global distribution of mating types shows limited opportunities for mating across populations of fungi causing boxwood blight disease

Boxwood blight is a disease threat to natural and managed landscapes worldwide. To determine mating potential of the fungi responsible for the disease, Calonectria pseudonaviculata and C. henricotiae, we characterized their mating-type (MAT) loci. Genomes of C. henricotiae, C. pseudonaviculata and two other Calonectria species (C. leucothoes, C. naviculata) were sequenced and used to design PCR tests for mating-type from 268 isolates collected from four continents. All four Calonectria species have a MAT locus that is structurally consistent with the organization found in heterothallic ascomycetes, with just one idiomorph per individual isolate. Mating type was subdivided by species: all C. henricotiae isolates possessed the MAT1-1 idiomorph, whereas all C. pseudonaviculata isolates possessed the MAT1-2 idiomorph. To determine the potential for divergence at the MAT1 locus to present a barrier to interspecific hybridization, evolutionary analysis was conducted. Phylogenomic estimates showed that C. henricotiae and C. pseudonaviculata diverged approximately 2.1 Mya. However, syntenic comparisons, phylogenetic analyses, and estimates of nucleotide divergence across the MAT1 locus and proximal genes identified minimal divergence in this region of the genome. These results show that in North America and parts of Europe, where only C. pseudonaviculata resides, mating is constrained by the absence of MAT1-1. In regions of Europe where C. henricotiae and C. pseudonaviculata currently share the same host and geographic range, it remains to be determined whether or not these two recently diverged species are able to overcome species barriers to mate.

Sexual reproduction of Zymoseptoria tritici on durum wheat in Tunisia revealed by presence of airborne inoculum, fruiting bodies and high levels of genetic diversity

Septoria tritici blotch (STB) caused by the heterothallic ascomycete Zymoseptoria tritici is currently one of the most devastating diseases of wheat worldwide. The extent of sexual reproduction of this pathogen is well documented on bread wheat, but not on durum wheat. The objective of the present study was to quantify the occurrence of Z. tritici sexual reproduction on durum wheat in the Tunisian environment. The assessment was undertaken using a triple approach combining fruiting body assessment, ascospore trapping and population genetic analyses. The results highlighted the formation of pseudothecia on leaves and stubble from the autumn until the end of the growing season. Likewise, qPCR monitoring highlighted a constant release of Z. tritici airborne inoculum during the wheat-growing season, with a peak of production at the end of the season. Genetic investigations using microsatellites revealed high levels of gene and genotypic diversities, an equal distribution of mating types, and a lack of genetic clustering within and between growing seasons. Taken together, these findings indicate that Z. tritici undergoes sexual reproduction on durum wheat in Tunisia at least to the same extent than on bread wheat in Western Europe, and that the dry and warm climate does not affect the mating process of the fungus. Frequent occurrence of sexual reproduction is a valuable knowledge to take into account in STB control strategies on durum wheat.

Cloning and analysis of Ophiocordyceps xuefengensis mating type (MAT) loci.

The entomopathogenic fungus Ophiocordyceps xuefengensis, a recently described species and identified as the sister taxon of Ophiocordyceps sinensis, is a desirable alternative to O. sinensis. The mating systems of fungi play a vitally important role in the regulation of sexual reproduction and evolution, but the mating type loci of O. xuefengensis were completely unknown. In this study, the mating systems of O. xuefengensis were analyzed. The conserved α-box region of the MAT1-1-1 and HMG-box of MAT1-2-1 were successfully obtained by PCR amplification. The distribution of both mating types in different tissues of wild and cultivated O. xuefengensis growth was detected and analyzed. The results showed that the asci always harbored both mating types, whereas the sclerotium, the stipe and each isolated strain of wild O. xuefengensis always had only one idiomorph, either MAT1-1 or MAT1-2, which confirmed that O. xuefengensis is heterothallic. The MAT1-1 locus of O. xuefengensis harbors MAT1-1-1, MAT1-1-2 and MAT1-1-3, and MAT1-2 contains the MAT1-2-1 gene. Southern blot analysis showed the MAT-1-1-1 and MAT-1-2-1 genes were single-copy in O. xuefengensis. These results will help to understand its life cycle and support artificial cultivation of O. xuefengensis.