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

Table 2. Modified Feekes Scale for Nassella neesiana panicle seed (adapted from Slay 2002c). Point 10 on the scale was called
the ‘boot stage’ by Pritchard (2002).
Feekes
Scale
Description of stage for N. neesiana
10 Flag leaf completely grown out, sheath swollen [boot stage]
10.1 Tips of awns emerged from swollen sheath
10.2 25% of heads emerged
10.3 50% of heads emerged
10.4 75% of heads emerged
10.5 100% of heads emerged; panicle free of sheath
10.5.1 Beginning of anthesis
10.5.2 Anthesis complete to top of panicle
10.5.3 Anthesis finished at base of panicle
10.5.4 No unopened flowers, stamens dropped, some seed developing
11.1 Milky ripe (milky dough stage)
11.2 Mealy ripe, seed contents soft but dry
11.3 Seed firm, chalky
11.4 Seed shedding
Tillers usually die after flowering and fruiting (as for grasses in general - Wheeler et al. 1999) usually within about 2 months
(personal observations). In southern Victoria the stems have usually browned off by mid January and begin to break down (D.
McLaren, 26 October 2006). The dry culms can remain standing for up to 6 months (Gardener et al. 1999) and generally persist
for several months before falling over and forming a dense mat that shades underlying vegetation (Gardener et al. 2005).
Cleistogene production
Separate hormonal influences appear to independently control panicle seed and cleistogene production (Connor et al. 1993).
Stem cleistogenes occur at two different periods:1. during the vegetative growth stage of the tiller - initiated in spring as single
spikelets under the leaf sheaths of young shoots, reaching maturity by the time of emergence of the aerial infloresence, and
released when the leaf sheaths weaken or rupture; and 2. during the flowering period, resulting in cleistogenes tightly enclosed
by the sheath and prophyllum (Connor et al. 1993). According to Slay (2001 2002c) basal cleistogenes are initiated after
seedlings establish and on older plants in autumn, and are maturing or mature by the time that panicle production and flowering
commences in mid spring. Stem cleistogenes are initiated as the stem elongates, and ripen by February. In southern Victoria,
non-basal stem cleistogenes have formed by the time that panicle seed is dropped and are possibly stimulated to mature by
panicle seedfall, and most stems have mature cleistogenes by the end of February (D. McLaren, 26 October 2006, based on
observations of Shiv Gaur). Slay (2001) observed that the non-basal stem cleistogenes are immature when panicle seed is
dropped, especially at the top node. Gaur et al. (2005) found that non-basal cleistogenes mature, and are shed, after the fall of
panicle seed.
Dyksterhuis (1945) found a similar phenology with N. leucotricha: axillary cleistogenes with endosperm in the dough stage were
present before anthesis of panicle flowers or before any panicle production. Seedlings were able to produce cleistogenes in the
dough stage by the age of 6 months, and cleistogene seedlings 9-10 months old, that were clipped to a height of 38 mm every
two weeks, produced very few tillers and on average less than half the cleistogenes (range of 0-3 cleistogenes per seedling) of
unclipped seedlings (range of 2-5) (Dyksterhuis 1945).
Slay (2002c) noted that the ability of an autumn germinating seedling to produce cleistogenes within 6 months means that the
species can survive as an annual.
Distribution
South America
Map: Gardener et al. (1996b) and Gardener (1998); records between 26º and 40º S from two herbaria and literature.
Argentina, Bolivia, Brazil, Chile, Ecuador, Peru, Uruguay (Torres 1997, Barkworth and Torres 2001, Martín Osorio et al. 2000,
Barkworth 2006). It is also known from Paraguay (Ramirez 1951,USDA ARS 2006, Zanin 2008) although presence in that
country was considered doubtful by Barkworth and Torres (2001) and Barkworth (2006). Longhi-Wagner and Zanin (1998) used
the name Stipa setigera C. Presl. for N. neesiana (“syn. S. neesiana Trin. and Rupr.”) and recorded it from Paraguay and
Columbia in addition to the countries already cited.
Considerable uncertainty remains in the understanding of the South American distribution due to confusing use of specific names
and differences of opinion about the actual identity of specimen material. Barkworth and Torres (2001), who did not refer to
Longhi-Wagner and Zanin (1998), considered S. setigera to be a synonym of N. mucronata (Kunth.) R.W. Pohl, and the two S.
setigera varieties hispidula and glabrata to be synonyms of N. neesiana, the latter synonymies established by Hitchock in 1925
(Torres 1993). They listed N. mucronata as present in Columbia, and did not list N. neesiana for that country. Zanin (2008)
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