Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
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potentially pathogenic: Alternaria sp., Colletotrichum sp., Drechlera spp., Phoma leveilli Boerma and Bollen and Phoma sp.<br />
Britt (2001) conducted a fungal pathogen survey at eight sites in Victoria and found four possible species <strong>of</strong> Alternaria, and one<br />
each <strong>of</strong> Aspergillus, Fusarium and Epicoccum on leaves, none <strong>of</strong> which was precisely identified. Leaf discoloration, spotting and<br />
necrosis was common in the field. Cultures on agar plates were distinguished by colour and form<br />
(downy/woolly/cottony/powdery). Testing showed that the fungi aided seed germination <strong>of</strong> N. neesiana but only Epicoccum sp.<br />
had a statistically significant effect, probably due to the small sample sizes. No seeds germinated in the absence <strong>of</strong> fungi. The<br />
effect could be due to fungal production <strong>of</strong> plant hormones, such as gibberellin, that break dormancy or stimulate germination, or<br />
to fungal digestion <strong>of</strong> the lemma. Growth substrates other than N. neesiana seed may be preferred by the fungi,so the effect may<br />
not occur under field conditions.<br />
As <strong>of</strong> 1998, none <strong>of</strong> the 27 species <strong>of</strong> fungi recorded from Austrostipa in <strong>Australia</strong> were recorded on Nassella spp. in <strong>Australia</strong>,<br />
nor do South American and <strong>Australia</strong>n Stipeae have any rusts in common (Briese and Evans 1998).<br />
Greene and Cummins (1958) recorded a single rust species on Austrostipa, Puccinia flavescens McAlp., with two known hosts,<br />
A. flavescens (Labill.) S.W.L. Jacobs and J. Everett, A. semibarbata (R.Br.) S.W.L. Jacobs and J. Everett. Vánky and Shivas<br />
(2008) recorded three smuts from Austrostipa in south-eastern <strong>Australia</strong> in addition to T. hypodytes: Fulvisporium restifaciens<br />
(D.E. Shaw) Vànky, Tranzscheliella minima (Arthur) Vànky and Urocystis stipeae McAlpine. The latter also occurs on<br />
Achnatherum spp. in south and east Asia (Vánky and Shivas 2008).<br />
Other biotic relationships<br />
Fungal and bacterial symbionts <strong>of</strong> Nassella spp. appear to be poorly known, apart from the observations <strong>of</strong> Britt (2001) (see<br />
“Pathogens” section, above). Higher plants in general have fungal endophytes that live within their tissues without causing<br />
damage, and plant roots are always inhabited by mutualistic fungi, usually classed as arbuscular mycorrhizal fungi,<br />
ectomycorrhizae or dark septate fungi (Khidir et al. 2009). Presence <strong>of</strong> these organisms can greatly affect the invasiveness <strong>of</strong> a<br />
plant and influence its ability to modify soil properties (Rout and Chrzanowski 2009).<br />
Grasses harbour large and diverse communities <strong>of</strong> root-associated fungi, including arbuscular mycorrhizal fungi (AMF), the<br />
colonisation <strong>of</strong> which appears to be strongly effected by climatic conditions and nutrient availability, and dark septate fungi,<br />
which are the main colonisers <strong>of</strong> <strong>grass</strong>es in semiarid environments (Khidir et al. 2009). No mycorrhizal relationships have been<br />
recorded for N. neesiana but vesicular arbuscular mycorrhiza have been reported for N. leucotricha and other stipoid <strong>grass</strong>es<br />
(Clark and Fisher 1986, Wang and Qiu 2006) and a dark septate fungus <strong>of</strong> the genus Paraphaeospheria sp. has been recorded<br />
from Achnatherum hymenoides (Roemer & J.A. Schultes.) Barkworth (Khidir et al. 2009). 80% <strong>of</strong> surveyed land plant species<br />
are mycorrhizal (Wang and Qiu 1996) so the possibility that N. neesiana lacks these root fungi seems remote.<br />
Root associated fungi appear to be generalist species that inhabit a range <strong>of</strong> species in a community and across large areas<br />
(Khidir et al. 2009). Khidir et al. (2009) found that co-occuring <strong>grass</strong>es had a common flora <strong>of</strong> non-AMF groups from the<br />
Pleosporales, Agaricales and Sordariales, with Paraphaeospheria spp. (Pleosporales), Moniliophthora spp. (Agaricales) and<br />
Fusarium spp. (Hypocreales) most common, but AMF fungi (Glomus sp.) were also present. The dark septate fungi may enable<br />
the plant host to access nutrients, including N and P, and may play a role in drought and heat tolerance (Khidir et al. 2009).<br />
N fixation by free-living bacteria associated with <strong>grass</strong> roots has been recorded (Clark and Fisher 1986) and several African<br />
<strong>grass</strong>es are known to fix significant levels <strong>of</strong> N in their native habitats (Rossiter et al. 2003). Rout and Chrzanowski (2009)<br />
found that Sorghum halepense harboured a range <strong>of</strong> bacteria in its rhizomes known to fix N, and almost certainly able also to<br />
chelate iron and mobilise phosphorus.<br />
Species <strong>of</strong> Neotyphodium Glenn and their teleomorphic relatives Epichloë Tul. (Balansieae, Clavicipitaceae) are endosymbiotic<br />
non-pathogenic fungi found in an estimated 20-30% <strong>of</strong> graminoid species, mainly in <strong>grass</strong>es <strong>of</strong> the subfamily Pooidae (Moon et<br />
al. 2007, Rudgers et al. 2009). They are closely related to the ergot fungi, Claviceps spp., and are commonly called ‘<strong>grass</strong><br />
endophytes’ (Aldous et al. 1999). Each sexual species <strong>of</strong> Epichloë is associated with a particular <strong>grass</strong> tribe in North America or<br />
Europe, but the many asexual species, transmitted via seeds, are hybrids resulting from crosses between Epichloë species or<br />
between Epichloë and Neotyphodium species, that bear no such direct relationship with their range <strong>of</strong> hosts and may have<br />
‘jumped’ between tribes (Moon et al. 2007). Endophytes transmitted vertically (inherited) are more likely to evolve to be<br />
symbiotic than those that spread vertically by contagious spread, which are more likely to retain pathogenicity (Rudgers et al.<br />
2009). Some <strong>grass</strong> endophyte species, including some affecting Achnatherum species, cause poisoning in livestock, and many<br />
produce chemicals that deter attack by insects (Moon et al. 2007). Tests with the mollusc Deroceras reticulatum Muller indicate<br />
that the different secondary metabolites produced by Neotyphidium can deter or enhance feeding (Barker 2008). Other<br />
documented benefits from endophyte infection include drought tolerance, increased vigour and higher nutrient content.<br />
Within Stipeae, species <strong>of</strong> Neotyphodium/Epichloë are known to infect only Achnatherum species (Moon et al. 2007, Rudgers et<br />
al. 2009) except for an unknown species infecting Nassella viridula. Those currently known are Neotyphodium chisosum (White<br />
and Morgan-Jones) Glenn et al. and probable Epichloë amarillans from A. sibiricum (L.) Keng (Wei et al. 2007, Ren et al. 2008,<br />
Moon et al. 2007), N. chisosum from A. eminens (Cav.) Barkworth, N. gansuense Li and Nan and its morphologically and<br />
geographically distinct variety inebrians C.D. Moon and C.L. Schardl from A. inebrians (Hance) Keng, N. funkii K.D. Craven<br />
and C.L. Schardl from A. robustum and an undescribed species from A. sibiricum (Moon et al. 2007). Undetermined species are<br />
also known from A. lobatum (Swallen) Barkworth, A. purpurascens (Hitchcock) Keng, A. splendens (Trinius) Nevski and A.<br />
viridula (Rudgers et al. 2009). The last has been classified as Nassella viridula by Barkworth (2006) who suggested it may be an<br />
alloploid between Nassella and Achnatherum.<br />
No evidence appears to be available on the presence or absence <strong>of</strong> endophytes in N. neesiana. But given their importance to<br />
plant fitness, endophyte presence should be investigated. In the USA endophyte infection <strong>of</strong> the non-native Festuca arundinacea<br />
Schreb. increases its invasiveness and impact on biodiversity (Rudgers et al. 2009).<br />
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