the endophyte community of spotted knapweed (centaurea ... · 2005) show the absence of catechin...
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The endophyte community ofspotted knapweed (Centaureamaculosa Lam., Asteraceae)
Alexey Shipunov, Anil Kumar Raghavendra,George Newcombe
Department of Forest Resources, University ofIdaho, Moscow, Idaho 83844-1133
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Spotted knapweed
Spotted knapweed (Centaureamaculosa Lam., but moreacceptable name is Centaureastoebe L.) is a noxious, invasiveplant which was introduced intoNorth America from Eurasia in the19th century. There are tworaces: diploids (biennials) andtetraploids (perennials), only thelast is present in North America.
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“Novel weapons”
Many invasive North Americanplants have been reported tohave antimicrobial,antiherbivore and allelopathiceffects, which are mostprobably the consequences ofunique (for American flora)secondary chemicalcompounds.
(From Cappucino & Arnason, 2006):invasive plants share their prominentsecondary compounds with less nativeNorth American plants than non-invasiveplants
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Catechin or not catechinSpotted knapweed is among plants which havesignificant phytotoxic (allelopathic) effect. Somesecondary compounds were believed to have this effect:cnicin and catechins.
Cnicin (sesquiterpene lactone) was extractedfrom aerial parts of knapweed in 1967 andhas been thought as main inhibitor ofneighbor plants growth (Kelsey & Locken,1987). However, some reporters told aboutlittle inhibitor effect of cnicin (Muir & Majak,1983)
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CatechinsThe most accepted opinion(Callaway et al., 1999 andmany others) is that cathechin-contained root exudates arecapable to suppress the growthof native grasses (Festuca,Koeleria etc.) and other plants.
However,recentexperiments(Blair et al.,2005) show theabsence ofcatechin effect.
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Fungal endophytes1) Inhabit every plant
2) Some endophytes areknown to producesecondary metaboliteswhich are beneficial tothe host plant
3) Have full spectrum fromparasitism tocommensalism
Therefore, the controversy could be explained ifinvestigated plants have different endophytecommunities and, as a consequence, differentsecondary compounds
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Competition experiment
Fescuealone:control
Endophyte-free (E–)knapweed and fescue
E+knapweedand fescue
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The differences in fescuebiomass are statistically
significantLeast Squares Means
1 2 CVAR00002
0
2
4
6
VAR00001
1 E– plants
2 E+ plants
C Control(Festucaidahoensisalone)
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Liquid cultures and volatilecompounds
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At least someendophytescan produce
sesquiterpenes
Gas chromatogram:highest pikecorresponds withsesquiterpene
We have also found thatthis particular endophytestrain has the insecticideeffect to weevils.
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Endophytes and seedgermination
Experimentwith
knapweedseeds
(fungal cultureswere used )
Experimentwith
Festucaidahoensis
seeds(liquid culturefiltrates were
used, we tried toimitate Blair et al.,2005 experiment
conditions)
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Some endophytes are capableto suppress seed growth
More than 2/3 endophytestrains have statisticallysignificant terminationeffect on Festucaidahoensis seeds,whereas only 1/4 of themhave similar effect onknapweed seeds.Moreover, someendophytes (Pleosporasp.) can kill fescueseeds.
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Endophyteshave different
effects onknapweed
Endophyte strain 124(Fusarium sp.) suppresses theflowering of knapweed
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Did fungi come with their hosts?
Two possibilities: “host-jumping” or co-introduction
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Endophytes are usuallyisolated from the achenesof knapweed
endophyte-free achenes
Isolation
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How diverseare
knapweedendophytes?
One of best MP trees from phylogenetic analysis of ITS1, 5.8S and ITS2 gene sequences.More then 65% of them have no exact matches in the NCBI GenBank nucleotide database.
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Botrytisspp., 6 ITShaplotypes
Fusariumspp., 5 (allare newtoGenBank)Alternaria
spp., 5
Mostfrequent ITShaplotypes
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Alternariaallergene gene
(alt a 1) wasused to identifyAlternaria and
Ulocladiumspecies
Majority rule consensus tree from MP analysis of “Alt a 1” gene sequences
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Distributionamong
native andexoticranges
Present inbothranges
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Are endophyte communitiesdifferent?
nativerange
exoticrange
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Patterns of co-occurrence
Haplotypescommon tonativerange
ITShaplotypescommon toexoticrange
Toboth
At the time, we have support for both co-introduction and“host-jumping” hypotheses.
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Endophyte-free plantsPlants from natural habitats are usuallyrich of endophytes (70%–90% of seeds).However, some of our samples contain noendophytes. We cultivated the 2ndgeneration of knapweed and inoculatethem with liquid fungal cultures on theflowering stage.
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Re-isolation
Then re-isolation were done.From all plants, we obtainedonly endophytes which wereused for inoculation.Alternaria species have thebest re-isolation frequency.No endophytes wereisolated from the control.Thus, we have found theway to produce endophyte-free plans.
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Sampling-2006
We are tryingnow to organize
much widersampling and
need your help!
Accumulation curve for 2004/2005(most of samples were collected inIdaho state or in southwesternEurope)
Places of interest
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Acknowledgements• Cort Anderson
• Rebecca Ganley
• Sanford Eigenbrode
• Hongjian Ding
• Maryse Crawford
• The team of R project for statistical computing
• Jari Oksanen, author of “vegan” R package forvegetation ecologists
• Idaho State Government
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Web-site of the project
http://uidaho.edu/~shipunov