Документ взят из кэша поисковой машины. Адрес оригинального документа : http://herba.msu.ru/shipunov/knapweed/pres_botany2006.pdf Дата изменения: Tue Aug 8 11:00:00 2006 Дата индексирования: Mon Oct 1 22:21:21 2012 Кодировка:

The endophyte community of spotted knapweed (Centaurea maculosa Lam., Asteraceae)

Alexey Shipunov, Anil Kumar Raghavendra, George Newcombe
Department of Forest Resources, University of Idaho, Moscow, Idaho 83844-1133


Spotted knapweed

Spotted knapweed (Centaurea maculosa Lam., but more acceptable name is Centaurea stoebe L.) is a noxious, invasive plant which was introduced into North America from Eurasia in the 19th century. There are two races: diploids (biennials) and tetraploids (perennials), only the last is present in North America.


"N o v e l w e a p o n s "
Many invasive North American plants have been reported to have antimicrobial, antiherbivore and allelopathic effects, which are most probably the consequences of unique (for American flora) secondary chemical compounds.

(From Cappucino & Arnason, 2006): invasive plants share their prominent secondary compounds with less native North American plants than non-invasive plants


Catechin or not catechin
Spotted knapweed is among plants which have significant phytotoxic (allelopathic) effect. Some secondary compounds were believed to have this effect: cnicin and catechins.

Cnicin (sesquiterpene lactone) was extracted from aerial parts of knapweed in 1967 and has been thought as main inhibitor of neighbor plants growth (Kelsey & Locken, 1987). However, some reporters told about little inhibitor effect of cnicin (Muir & Majak, 1983)


The most accepted opinion (Callaway et al., 1999 and many others) is that cathechincontained root exudates are capable to suppress the growth of native grasses (Festuca, Koeleria etc.) and other plants.

Catechins

However, recent experiments (Blair et al., 2005) show the absence of catechin effect.


Fungal endophytes
1) Inhabit every plant 2) Some endophytes are known to produce secondary metabolites which are beneficial to the host plant 3) Have full spectrum from parasitism to commensalism Therefore, the controversy could be explained if investigated plants have different endophyte communities and, as a consequence, different secondary compounds


Competition experiment
E+ knapweed and fescue

Fescue alone: control

Endophyte-free (E­) knapweed and fescue


The differences in fescue biomass are statistically significant
Least Squares Means
6 1 0 04 0 0 R A V2

1 E­ plants 2 E+ plants C Control (Festuca idahoensis alone)
1 2 C VAR00002

0


Liquid cultures and volatile com pounds


Gas chromatogram: highest pike corresponds with sesquiterpene

At l east s o m e endophytes c a n p ro d u c e sesquiterpenes
We have also found that this particular endophyte strain has the insecticide effect to weevils.


Endophytes and seed germination

Experiment with knapweed seeds
(fungal cultures were used )

Experiment with Festuca idahoensis seeds
(liquid culture filtrates were used, we tried to imitate Blair et al., 2005 experiment conditions)


Some endophytes are capable to suppress seed growth
More than 2/3 endophyte strains have statistically significant termination effect on Festuca idahoensis seeds, whereas only 1/4 of them have similar effect on knapweed seeds. Moreover, some endophytes (Pleospora sp.) can kill fescue seeds.


Endophytes have different effects on knapw eed

Endophyte strain 124 (Fusarium sp.) suppresses the flowering of knapweed


Did fungi come with their hosts?

Two possibilities: "host-jumping" or co-introduction


Isolation
Endophytes are usually isolated from the achenes of knapweed

endophytefree achenes


H o w d iv e rs e a re knapw eed endophytes?

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.


M ost frequent ITS haplotypes

Botrytis spp., 6 ITS haplotypes

Alternaria spp., 5

Fusarium spp., 5 (all are new to GenBank)


Alternaria a lle rg e n e g e n e (a lt a 1 ) w a s used to identify Alternaria and U lo c la d iu m s p e c ie s
Majority rule consensus tree from MP analysis of "Alt a 1" gene sequences


Distribution am ong native and exotic ra n g e s

Present in both ranges


Are endophyte communities different?
exotic range

native range


Patterns of co-occurrence
ITS haplotypes common to exotic range To both

Haplotypes common to native range

At the time, we have support for both co-introduction and "host-jumping" hypotheses.


Endophyte-free plants
P la n ts fr o m n a tu r a l h a b ita ts a r e u s u a lly r ic h o f e n d o p h y te s ( 7 0 % ­ 9 0 % o f s e e d s ) . H o w e v e r , s o m e o f o u r s a m p le s c o n ta in n o e n d o p h y te s . W e c u ltiv a te d th e 2 n d g e n e r a tio n o f k n a p w e e d a n d i n o c u la te th e m w ith liq u id fu n g a l c u ltu r e s o n th e flo w e r in g s ta g e .


Re-isolation
Then re-isolation were done. From all plants, we obtained only endophytes which were used for inoculation. Alternaria species have the best re-isolation frequency. No endophytes were isolated from the control. Thus, we have found the way to produce endophytefree plans.


S a m p lin g -2 0 0 6
Accumulation curve for 2004/2005 (most of samples were collected in Idaho state or in southwestern Europe)

We are trying now to organize much wider sampling and need your help!
Places of interest


· Cort Anderson

Acknowledgements

· Rebecca Ganley · Sanford Eigenbrode · Hongjian Ding · Maryse Crawford · The team of R project for statistical computing · Jari Oksanen, author of "vegan" R package for vegetation ecologists · Idaho State Government


Web-site of the project

http://uidaho.edu/~shipunov