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

also based on a misunderstanding of the breeding system (see Britt 2001 pp. 86-87): all the panicle seed is not necessarily crossfertilised
(see the observations of floral anatomy by Burbidge and Gray (1970) and Vickery et al. (1986) above), the basal
spikelets in a panicle are more or less cleistogamous, while cleistogamous spikelets can be found anywhere in the panicle. In
order to reach such a concluison a methodology was required that ensured only the sampling of DNA from chasmogamous seeds.
The local populations could also be the offspring of separate founder events involving different South American source
populations, with the lack of local polymorphism (if it is not an artefact) resulting from genetic bottlenecking.
As with most such studies these appear to be rather random probings of the genome, the genetic material examined is not
necessarily expressed in the phenotype, nor is its functional role known. Future molecular genetical work in this area should start
with an examination of South American populations ascribed to particular varieties and should also be integrated with a study of
morphological variation, as suggested by Britt (2001).
Phenology, growth and productivity
Within the revised Raunkiaer plant life form spectrum (Mueller-Dombois and Ellenberg 1974), N. neesiana is classified as a
hemicryptophyte (a perennial herb with periodic shoot reduction), subtype ‘caespitose graminoids’ (bunched or circular shoot
arrangement with shoots more or less at the soil surface) and probably as 3.103 “sparingly evergreen during unfavourable
season”.
N. neesiana grows predominantly over the coooler months (Muyt 2001) with vegetative growth mainly from autumn to spring
(Snell et al. 2007). Storrie (2006) considered it “one of the few” major weedy grasses in New South Wales “that produces green
feed in winter”. In Argentina both agronomists and landholders agreed that it produced a large amount of good livestock feed
during winter (Gardener et al. 1996b). High rainfall in spring promotes panicle proliferation (Cook 1999). Flowering and fruiting
occurs from September to March in South America (Zanin 2008). In south-eastern Australia flowering occurs mainly during
spring and early summer (September to December), but can occur at other times of the year when moisture and temperature
conditions are suitable (Snell et al. 2007).
At Inverleigh, Victoria, Gaur et al. (2005) recorded plants in the vegetative phase to 3 October 2003 and 1 October 2004, flag
leaf swelling over the developing panicle on 13 October 2003, spiky stems on 18 October 2004 and full panicle emergence on 27
October 2003 and 28 October 2004. Pritchard (2002) recorded that plants at Laverton North had panicles still concealed in the
sheath on 3 October 2000 and all the foliage was green, and that on 15 November there was a dense covering of emerged
panicles. In Italy N. neesiana flowers and fruits from May to July (Moraldo 1986) approximately 6 months out of phase with
Australia, where bolting generally begins in mid October and panicle seed drops in mid December (D. McLaren in Iaconis
2006b). Slay (2002c) reported a similar phenology in New Zealand: elongation of reproductive tillers in spring with the main
flush of tiller production from mid-September to mid-October, flag leaf swelling in mid-October, then 24 days between the first
emergence of the panicle and anthesis. Slay (2001) found the period from the boot stage to anthesis was 36 days and from
anthesis to 100% viability of seed was 33 days.
Slay (2001) identified: three phases of seeding: 1. basal cleistogene production during vegetative growth of the tiller, initiated in
autumn and completed in spring before anthesis of panicle flowers; 2. cleistogamous and chasmogamous seed production in the
panicle; 3. cleistogene production on the stems, initiated before anthesis of panicle flowers and completed after panicle seed
maturation.
In Victoria stems are brown and breaking down and cleistogenes form in mid to late summer, and by the end of February most
stems have cleistogenes (McLaren in Iaconis 2006b). In New Zealand old culms are easily broken by late March (Slay 2001).
The inactive period from mid summer to the time of autumn rain has been inadequately documented and summer dormancy
appears to have been widely assumed. However flowering is indeterminate (Grech 2007a) and plants are known to flower in
response to summer rain (Bedggood and Moerkerk 2002). Senescence of foliage and cessation of leaf growth occurs in all
grasses in response to drought, but truly summer-dormant grasses display these traits despite summer irrigation (Norton et al.
2008). Across the range of pasture grass taxa there is a continuum of responses from full dormancy to non-dormancy, and the
intensity of summer dormancy can be assessed by simulating a mid summer storm in the midst of drought, and measuring
subsequent herbage production or senescence (Norton et al. 2008). Full dormancy is supposedly characterised by complete
cessation of growth, full herbage senescence and dehydration of young leaf bases, whereas senescence and partial growth
cessation may be just a dehydration avoidance strategy which can be expressed in any season under conditions of soil moisture
stress. The possession of true summer dormancy is supposedly critical for pasture grass persistence in the drought prevalent
pastures of south-eastern Australia, so a number of commonly utilised exotic grass cultivars have been assessed for this
characteristic (Norton et al. 2008). Assessments of weedy and native Poaceae, including N. neesiana, would be informative.
Average production in New England pasture was 2.3 t ha -1 y -1 (Gardener et al. 2005). Slay (2001) recorded production of 5.5±0.5
kg ha -1 of dry matter per day during the first 48 days after mowing in November in New Zealand. Grech (2004) found that plants
that were regularly clipped to simulate grazing produced more digestible growth (significantly more crude protein, metabolisable
energy and digestible dry matter) than unclipped plants. N fertiliser (100 kg ha -1 in two applications) increased the feed value
only at the seedhead stage.
Crude protein levels of green leaves (in South America) were 6.3-18.3% (Gardener et al. 1996b). Crude protein levels of winter
foliage regrowth after clipping in Australia were 12.7-16.6% and digestible dry matter of green leaf material was c. 60% (range
58-66%), compared to Festuca arundinacea with crude protein of 13.0-18.8% and digestible dry matter 62-69% (Gardener,
Storrie and Lowien 2003, Gardener et al. 2005). Culm material had a crude protein content of 4.5%. New Zealand data indicates
a crude protein level of green leaves of plants in the vegetative phase of 14.5%, while leaves of plants early in the flowering
stage had a crude protein level of 6.4%. The metabolisable energy value of vegetative phase leaves was 7.7 in early summer and
of 7.5 in early flowering. Comparable crude protein and metabolisable energy (ME) levels were 9.9% and 11 for Lolium perenne
L., while ME values in summer 1991 for D. glomerata, L. perenne, Phalaris aquatica L. and Festuca arundinacea were 8.3, 7.5,
33