Literature review: Impact of Chilean needle grass ... - Weeds Australia

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