Paul Cannon and Ester Gaya Introduction to the Ascomycota

Introduction to the Ascomycota

Paul Cannon and Ester Gaya © RBG Kew Introduction to the Ascomycota

The Ascomycota ‐overview

• Two thirds of all fungi belong to the Ascomycota – Probably approaching 2 million species in the world 1,2,3 – 10000‐11000 species, well over 1000 genera known from Great Britain & Ireland – Many groups are more diverse in the tropics 4

1 Hawksworth doi:10.1017/S0953756201004725 2 O’Brien et al. doi: 10.1128/AEM.71.9.5544‐5550.2005 3 Hawksworth & Lücking, doi:10.1128/microbiolspec.FUNK‐ 0052‐2016 4 Aime & Brearley doi: 10.1007/s10531‐012‐0338‐7

A New Classifica on for Fungi (Hibbe et al. 2007, McLaughlin et al. 2009)

Phylogeny of the Ascomycota

Phylogram from Hibbett et al., Mycological Research, 2007 doi 10.1016/j.mycres.2007.03.004

• In most fungi, the mycelium is haploid for almost all of the life cycle, and hyphae contain multiple nuclei that may not be genetically identical • In the Ascomycota, meiotic spores are produced within specialized cells, the asci • The only diploid phase occurs within the crozier, a specialized cell that develops into the ascus following a meiotic (and usually a further mitotic) division

Image © David Malloch, New Brunswick Museum

The Ascomycota – reproductive dimorphism

• Many Ascomycota reproduce both sexually and asexually • Reproductive structures often look completely different, and are rarely present simultaneously • Until recently biological links between sexual and asexual morphs were often difficult to establish

• This led to establishment of a dual nomenclatural system, that has only recently been dismantled

Morphs and linkages

• Conidial morphs (anamorphs): vegetative reproduction via asexual spores (conidia) • Fragmentation of hyphae • Soredia and isidia – asexual morphs of lichenized species • Andromorphs: structures producing spermatia (male gametes) • Sexual morphs (teleomorphs): structures producing asci and ascospores

Linkages via: • Consistent association • Sequential observation • Culture (usually of the sexual morph) • Genomic analysis

Associations and nutritional strategies • Like other fungi, members of the Ascomycota depend on other organisms for energy • Perhaps 80% of all species* are directly dependent on plants. • They may be: – saprotrophs (eating dead tissues) – necrotrophs (killing and eating tissues) – biotrophs (extracting nutrition from living tissues) – symbionts (exchanging substances/services for nutrition) • Around 25% of all species* form lichen associations with algae and/or cyanobacteria

* Kirk et al., Dictionary of the Fungi, 2008 © RBG Kew Introduction to the Ascomycota

Survey and monitoring challenges • Most non‐lichenized members of the Ascomycota are small and cryptic with ephemeral fruit‐bodies • Survey methods include: – Direct observation [inefficient and labour‐intensive, difficult to replicate, weather‐dependent, usually impossible for non‐fruiting taxa] – Culture [labour‐intensive, methods favour weedy species, many not culturable at all, identification difficult especially non‐fruiting] – Molecular primers [expensive, only possible for detection of particular species] – Molecular environmental sampling [methods need development, some quantification possible, problems in correlation with traditional data] • Lichen surveys are much less problematic [but not representative of the Ascomycota as a whole]

Literature: Mueller et al., Biodiversity of Fungi. Inventory and Monitoring Methods, 2004; Cannon, doi 10.1023/A:1018362002273 © RBG Kew Introduction to the Ascomycota

Identification and classification • Many features used in identification are poor predictors of phylogeny

– Limited number of appropriate responses to competitive stimuli – the four‐legged mammal syndrome – Convergent evolution of external features – Influence of host/substrate – Useful features for ID such as spore septation and coloration have evolved many times But: • Morphology is still an essential tool for identification of many groups • Sequence data are essential for identification of cryptic species

Fruit‐bodies of the Ascomycota

Absent – yeasts*, hyphomycetes* (including synnemata and sporodochia)

Open – apothecia (flat or cup‐shaped – “discomycetes”), mazaedial fungi, most lichens

Nearly closed – perithecia (“pyrenomycetes”), loculoascomycetes, pycnidia

Closed – cleistothecia (“plectomycetes”), truffles*, thyriothecia, pycnothyria, acervuli

Compound (eu‐ and pseudo‐stromatic, teleomorphic and anamorphic)

Fruit‐bodies of the Ascomycota: convergence

Phylogram from Boehm et al., Mycologia, 2015

doi:10.3852/14‐191

Asci and their morphology

Passive discharge thin‐walled, globose or saccate

Active Unitunicate elongate with dis‐ (one‐ thickened charge layered) apex, often with a ring

Fissitunicate elongate, (bitunicate, usually with two‐ an ocular layered) chamber

Conidial production: proliferation

Sympodial – conidia formed Percurrent – conidia formed in from successive loci sequence from a single locus

Important groups ‐ Pezizales

The operculate discomycetes. Worldwide occurrence, with often large and colourful fruit‐ bodies found on/in soil, rotten wood and dung. Some species (including truffles) are ectomycorrhizal with tree roots. Ascospores aseptate, large, sometimes ornamented.

Important groups ‐ Helotiales The inoperculate discomycetes. Fruit‐bodies usually small and often colourful, sometimes with hairs, sometimes stalked. Asci small and thin‐walled, usually with an apical ring. Found associated with living or dead plant tissues, sometimes host‐specific. Some species are pathogens.

Important groups ‐ Eurotiales Ubiquitous saprotrophs, usually with cleistothecial ascomata and dominant hyphomycetous anamorphs with complex conidiophores forming chains of conidia. Highly diverse chemically, economically critically important as pharmaceutical and toxin producers.

Important groups ‐ Xylariaceae Important as endophytes and saprotrophs, a few pathogens. Most species have complex stromatic fruit‐bodies with multiple perithecia, producing dark brown aseptate ascospores with germ slits. Widespread wood‐ and bark‐associates in both temperate and tropical biomes

Important groups ‐ Erysiphales The powdery mildews. A group of biotrophic pathogens with dominant anamorphs producing white sheets of conidiophores on living leaves, followed by cleistothecial ascomata which sometimes have complex appendages. Some are economically important.

Important groups ‐ Nectriaceae Saprotrophic or parasitic fungi with brightly coloured perithecia and prominent hyphomycetous anamorphs. Some (especially species of Fusarium s.l.) are important plant pathogens. Widespread in both temperate and tropical regions.

Important groups ‐ Pleosporales A very large group of fungi with perithecial stromata, fissitunicate asci and very varied ascospores. Anamorphs are prominent in some families, and some are important plant pathogens.

Important groups ‐ Capnodiales An important and widepread group of fungi with diverse and prominent asexual morphs and many necrotrophic plant pathogens. The sexual morphs are perithecial with fissitunicate asci and no interascal tissue, and vary very little in form.

Important groups ‐ Taphrinales A small basal lineage of plant pathogens causing galls and witches’ brooms on stems, leaves, fruits and flowers. No fruit‐bodies are formed, with the asci forming in a palisade on the plant surface. Anamorphs are yeast‐like.

Important groups ‐ Geoglossales A small basal lineage of black club‐shaped fungi with an exposed, sometimes spinose hymenium covering the upper part of the fruit‐body. They appear to be very sensitive to nitrogen pollution, and their nutritional status needs confirmation.