Rust fungi

Paul Smith

All photos copyright of Paul Smith

Outline

• What are rust fungi?

• Life cycles of rust fungi

• Oddities – galls and parasites

• Finding and recording rust fungi

• A few common rusts to look out for

What are rust fungi?

• Plant parasitic fungi with very specialised lifestyles

• Two big groups of fungi

– Ascomycetes – many moulds, plant parasites and decay fungi

– Basidiomycetes – mushrooms and toadstools, rusts and smuts

• Rusts are very unusual ‘basidios’

What are rusts?

• The name comes from the colour of the spores

• Spores are generally all that is visible

• There is some mycelium (fungal tissue) in the host, to gather nutrients

• Most rusts can’t be grown away from their hosts, even under specialised conditions

Puccinia glomerata on ragwort

Puccinia coronata on Yorkshire fog

Rust life cycles

• Initial infection is from a basidiospore, from which fungus grows inside host

• This first infection produces spermogonia with 0’s (spermatia) – often barely visible

• Two infections combine, and combination gives rise to new pustules containing I’s (aecia) – Like clusters of balls when developing

– Rupture to show spores, looking like volcanoes

– Usually early in the year

Uromyces dactylidis I on Celandine

Puccinia urticata I on Nettle

Life cycles (cont)

• I’s generally infect the alternate host, a different species

• The new infection on the new host gives rise to new pustules containing II’s (uredinia) – Rustiest stage? Rust-coloured, powdery

– Spores usually spiky or warty

• II’s can infect new plants of the same species to make more II’s – Some species persist as II’s

Puccinia calcitrapae II on Hardheads

Puccinia hydrocotyles II on marsh pennywort

Life cycles (cont)

• Same infection leads to IIIs, the “perfect” state

– IIIs are resting stage – overwinter, typically found late in year

– Spores usually smooth

– Can be 1, 2 or many-celled (taxonomy)

• When conditions right, IIIs germinate to form tiny fungus with basidia, makes IV’s (basidiospores)

– Short-lived

– Infect new hosts…

Puccinia obscura III on Woodrush

Puccinia cnici III on Spear Thistle

Uromyces rumicis III on Sheep’s Sorrel

Phragmidium violaceum III on Bramble

Variants of life cycles

• Some rusts do all stages on one host – Puccinia punctiformis on Creeping Thistle

• A few species have only some stages – Trachyspora intrusa I, III on Lady’s-mantles

• Several species have only one spore stage – Uromyces muscari III on Bluebell

– Puccinia epilobii III on Willowherbs

– Chrysomyxa empetri II on Crowberry (IIIs known, but not in Britain)

Trachyspora intrusa I on Lady’s-Mantle

Oddities – galls and parasites

• A number of rusts cause reactions in their hosts leading to galls – some quite pronounced – Puccinia urticata I on Nettle

– Puccinia circaeae III on Enchanter’s Nightshade

• Several other fungi parasitise rusts – hyperparasites – Eudarluca caricis has cleistothecia in pustules

– Tuberculina persicina on surface

Puccinia urticata I on Nettle

Triphragmium ulmariae I on Meadowsweet

Eudarluca caricis

Tuberculina persicina

• Image removed for copyright reasons – available at http://tolweb.org/onlinecontributors/app;jsessionid=0A5424DA78FC660793DF56A1

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Finding and recording rusts

• Finding

– Learn which plants have rusts (and when!)

• Unexpected species do – ferns, conifers

– Look for yellowed or manky leaves, look at undersides…start in your garden!

– search pattern develops with experience

– Be prepared to spend time searching!

Puccinia graminis on Mahonia

Gymnosporangium cornutum on Juniper

Recording

• ID – Most plants hosts have only 1 rust; at most a few – Ellis & Ellis Microfungi on land plants – Henderson Guide

http://www.aber.ac.uk/waxcap/downloads/ Henderson2004-BritishRustFungiHostPlantGuide.pdf

– Generally need to check spores under microscope

• Recording – Just like other groups, but also handy to have info on

hosts, spore stages and parasites if any – FRDBI

Coleosporium tussilaginis I on Black Pine

Coleosporium tussilaginis I on Black Pine

A few spring rusts to look for…

• Uromyces muscari III on Bluebell

– Dark brown spores, a group of sori forming a patch on a leaf

• Puccinia punctiformis 0, I on Creeping Thistle

– Infected shoots spindly and covered with spores

– Smells of honey

• Puccinia lagenophorae I on Groundsel, Ragwort etc

Puccinia punctiformis on Creeping Thistle

Thank you! Puccinia chaerophylli on Sweet Cicely