(SUB)MICROSCOPIC INVASIVE

SPECIES

• Categories of submicroscopic invasive species

• Consequences of their occurrence in Croatia

• Pathogenicity (infectivity, virulence) vs. invasiveness

• Control strategies

(SUB)MICROSCOPIC INVASIVE

SPECIES

In databases, often under 100 worst and/or listed as neither

plants nor animals.

www.invasive.org – North America invasive species

Categories: plants, animals, diseases, other species

http://www.iucngisd.org/gisd/search.php - Global invasive

species database has virus, bacteria, fungi categories

DAISIE – European database, bacteria, fungi…not many

Invasiveness – impact on ecosystem (biodiversity) and/or

human activities

Importance of other factors (vectors, biology…)

Algae, planktonic organisms (diatoms, dinoflagellates), fungi,

oomycetes

Bacteria

Viruses

Subviral pathogens:

ViroidsCoconut cadang cadang viroid (CCCVd)

PrionsChronic waisting disease (CWD)

Others – deficient classification at different taxonomy levels

(incertae sedis)

CRYPHONECTRIA PARASITICA

Class Sordariomycetes, order Diaporthales, family Cryphonectriaceae

Aggressive phytopathogenic fungus, amongst 100 worst –

serious threat to biological diversity. It causes chestnut blight.

Infects wood through bark cracks and leads to chestnut tree

disease and death – canker, callusing canker, biocontrol.

C. parasitica lifecycle and dissemination

Invasion history

C. parasitica – very pathogenic in European and American

chestnuts but not in East Asian species.

Fungus-host coevolution- Japanese and Chinese chestnuts

very tolerant to infection. Both plant and fungus can survive

and reproduce.

North American scenario

American chestnut (Castanea dentata) – very sensitive, over

40 years, 3.5 billion trees destroyed.

American chestnut distribution pattern before the introduction of

the fungus in 1904.

European scenario

European chestnut – sensitive but infecting fungus is mostly of

hypovirulent strain.

European chestnut

distribution pattern

(Castanea sativa Mill.)

Chestnut blight first recorded in 1938 near Genoa. It spread to

all chestnut growing regions in Europe. In Croatia, first recorded

near Opatija in 1955.

Hypovirus

Cryphonectria hypovirus 1-4 (CHV-1 to -4) - dsRNA detected

in the fungus cytoplasm but the virus has +ssRNA genome.

It has no capsid proteins. Virus like particles in the fungus

cytoplasm.

It modifies fungus transcriptome.

In Europe, out of 4 viruses only CHV-1 recorded.

It reduces parasitic growth of the fungus and its sporulation

capacity resulting in lowered pathogenicity and invasiveness.

Virus distribution in nature:

• vertical– by asexual spores (conidia) 1-99%, requires

moisture (mainly splash distribution 1-2 m) but possible by

birds, mites and wind

• horizontal – hyphal fusion amongst vegetatively compatible

(vc) types of fungi

• human activities – uncontrolled plant import and trade, biocontrol efforts

Biocontrol by a hypovirus depends on vc types (fungus), the

mode of its distribution in nature, on the virus type (CHV-1 is

good biocontrol agent in Europe).

C. parasitica and CHV sampling sites in Croatia

Prof. Mirna Ćurković-Perica kindly provided slides 4-11.

Phytoplasmas

class Mollicutes

• intracellular phytopathogenic bacteria, pleomorphic 200-800 nm, MLOs (mycoplasma-like organisms) until 1993.

• Taxon ‘Candidatus Phytoplasma’ – members cannot be

cultured in axenic media.

• Parasites in two kingdoms – plant phloem and insects feeding

on plant sap (Cixiidae, Psyllidae).

• In plants, they cause serious diseases but usually not in

insects!

Grapevine Phytoplasmas

• cause Grapevine Yellows diseases (GY) - 8 taxa.

•The most important GY agents in Europe:

Flavescence Dorée (FD)

– quarantine pathogen

Bois Noir (BN), Vergilbungskrankheit (VK), Stolbur (Stol),

‘Ca. P. solani’ – endemic

Flavescence dorée phytoplasma (FDp)

• FDp first recorded in1950s in SW France.

• Scaphoideus titanus Ball – American Nearctic ampelopfagous cicadellidinsect is the principal vector in Europe.

• AldYp and PGYp are similar to FDp – quarantine pest and epidemicdisease agent.

• Devastating disease, fast spread, epidemic nature (F, I, PT, CH, SLO, H,SRB, HR 2010).

In Croatia, Bois Noir (BN) is also important. Polyphagous

Hyalesthes obsoletus Sign. is the main vector. It feeds on the

grapevine occasionally but prefers weeds.

bindweed nettleeggs in the roots

• FDp i BNp cannot be differentiated on the basis of symptoms!

Vitis vinifera L. ‘Pošip’

‘Plavac Mali’

• Identification by molecular tools (16S rDNA) and for the

molecular epidemiology MLST (multilocus sequence typing) is

required. Control strategies should be based on molecular

epidemiology data.

CTV virion 2000 x 11 nm, phloem

limited

Niblett et al. 2000, Virus Res. 71, 97-106.

Known from 1930s.

It destroyed 100 million citrus trees (SwO, mandarin, grapefruit

grafted on sour orange), new CTV foci even in the 21st century!

Citrus tristeza virus (CTV)

All tristeza faces Stem Pitting

(SP)

Photos: C. Roistacher

Quick Decline (QD)

Symptom expression depends on: rootstock/scion combination,

CTV strain (genotype), environmental factors.

Aphid vectors of CTV:

Toxoptera citricida (invasive!)

6-25x more efficient vector than Aphis

gossypii,

A. spiraecola,

Myzus persicae

CTV long-distance transfer by man!!!

Infected planting material (budwood (twigs), young grafted

plants).

T. citricida (foto G. Nolasco)

Citrus production in Croatia

Split

Dubrovnik

• 2 counties, 1500 ha

• Japanese mandarin

(Satsuma, C. unshiu)

300t/y, some lemon,

sweet orange

• Neretva River basin

• Institute for Adriatic Crops, Split – collection

Zagreb

CTV pilot study (2002-2004)

• CTV occurrence and distribution?

• Strains (biogrups) of CTV - virulence?

Mexican lime – universal indicator

Vein corking

Stem pitting

spooning

Vein clearing

gra

fting

Highly pathogenic CTV strains (SP, QD, SY) recorded

previously thought not to be present in the Mediterranean

basin.

Mixed infections are frequent (55%).

CTV populations have high variability, recombinant genotypes

are recorded.

64%

36%

1

2

55%

45%1

2

ELISA – 50% trees CTV-positive!

Satsuma/P.trifoliata combination is symptomless!

Similar results in Satsuma collection.

CTV-SP strains recorded in the northern Mediterranean –

coldest citrus growing area.

Satsuma mandarins are symptomless reservoir hosts

important for CTV distribution within and outside the country.

CTV populations and strains need to be monitored as well as

potential vectors especially since Toxoptera citricida arrived to

Portugal and Spain in 2003.

TRISTEZA !!!

• Emerging viruses

SARS

Avian flu

Nipah

Hendra

mumps

human metapneumovirus

bluetongue

Ebola

Monkey pox

Sin Nombre

Monkey pox

West Nile

Sin Nombre

Adapted from Carter&Saunders, 2007

West Nile virus (WNV) invasive in the USA.

WNV - Uganda 1937, recorded in the NYC only in 1999.

Flavivirus

East Africa, Middle East, Eastern Europ– occasional

outbreaks.

Transmitted by mosquitoes.

About 20% human cases results in a flu-like disease, less

than 1% out of the symptomatic cases presents neurological

complications (encephalitis).

Firs birds symptoms in birds of NY, than horses and humans.

Within 5 years, WNV spread to Canada, Mesoamerica, the

Caribbean's…in 2012 recorded in Croatia in humans but

before that in horses.

Intuitions:

WHO, EPPO, EU agencies, Croatian institutions

Parliament, Ministries and Agencies

Legislation (e. g. CTV):

CTV status in the EU is regulated by:

1) Directive EU 2000/29 Annex II/AII European isolates (EU Annex II /AI non

European isolates)

2) EPPO Quarantine A2 list.

CTV Status in Croatia additionally regulated by:

1) Ordinance - Pravilnik o mjerama za sprečavanje unošenja i širenja

organizama štetnih za bilje, biljne proizvode i druge nadzirane predmete i

mjerama suzbijanja tih organizama (NN 74/2006) Prilog 2 II-A-II te

2) Ordinance - Pravilnikom o stavljanju na tržište reprodukcijskog sadnog

materijala i sadnica za proizvodnju voća (NN 124/06)

EDUCATION, CONTROL, ERADICATION, CERTIFICATION!