Meredith Mitchell

LIGULE: An evaluation of indigenous perennial grasses for dryland salinity management in south-eastern Australia. 2. Field performance and the selection of promising ecotypes

This paper reports the results of an initial evaluation of a large collection of Australian perennial native grasses. The overall aim of the research was to identify accessions that may be useful for pastoral purposes and for controlling land degradation on hill-lands in the high (>500 mm) rainfall zone of south-eastern Australia. Accessions (807) representing 37 target species were established in spaced plant nurseries at Rutherglen and Wagga Wagga. Dactylis glomerata L. cv. Porto and Eragrostis curvula (Schrad) Nees. Complex cv. Consol were established as comparator (control) species. A range of attributes was observed over a 2-year period (19900—1992), including persistence, vigour, productivity, palatability, morphology, and characteristics related to seed production. Accessions were initially culled on the basis of their persistence. Data for a range of attributes were separately analysed using pattern analysis to provide a broad overview of the performance and characteristics of the remaining accessions. A number of selection criteria were applied which resulted in selection of a promising group of 20 accessions (12 species from 8 genera). The promising group of accessions will be evaluated further at field sites typical of hilly landscapes in the 500mp;mdash;600 mm rainfall zone of south-eastern Australia.

LIGULE*: An evaluation of indigenous perennial grasses for dryland salinity management in south-eastern Australia 1. A base germplasm collection

This paper reports on the collection phase of a research program which aimed to identify Australian native grasses that may be useful for pastoral purposes and for controlling land degradation on hill-lands in the high (>500 mm) rainfall zone of south-eastern Australia. Live plants of 37 target species were collected along a number of transects, and at specific locations, in New South Wales and Victoria. The collection sites were generally along public roads, and were chosen for their vegetation diversity. Each collection site was marked on a 1: 250000 topographic map, and detailed notes were taken of the native vegetation, geology, soil types, land use, and other features. Surface (00—10 cm) soil samples were collected at most sites and analysed for phosphorus, pH CaCl 2 , electrical conductivity, and particle size distribution. A total of 807 accessions were collected from 210 locations. At most collection sites, soils were acidic (median pH 5.6); soil phosphorus (Olsen) was in the low range (<8.5 mg/kg); and the target genera occurred with a low frequency (half of the sites yielded 3 accessions or less). Although genera collected in the study could be ranked on the basis of the mean pH of their collection sites, they all tolerated a considerable soil pH range (of about 2mp;mdash;5 pH units). Allowing root and shoot growth to recommence by growing collected plants for a short period in coarse sand considerably improved establishment success. Accessions collected in this study will be further evaluated.

Interaction of diet and long ageing period on lipid oxidation and colour stability of lamb meat

Eighty-four crossbred wether and ewe lambs were allocated to four finishing diets. The diets were: Lucerne pasture (n=24), Annual ryegrass with sub clover pasture (n=18), Standard commercial feedlot pellets (n=24) and Annual ryegrass based pasture and commercial feedlot pellets (500g/day/head) (n=18). After 8weeks of feeding the lambs were slaughtered and the m. longissimus (LL) and m. semimembranosus (SM) were vacuum packaged and held chilled for 5 (fresh) or 60 (long aged) days, after which samples of each were displayed for 4days under simulated retail conditions. Irrespective of muscle type the long aged samples exhibited a rapid reduction in redness (a*-values) and R630/580nm ratio values such that consumer acceptable thresholds for both traits were quickly exceeded providing limited shelf life. Long ageing also lead to high TBARS levels measured as MDA mg/kg muscle suggestive of a product likely to exhibit rancidity and off flavours from lipid oxidation.

Population biology of Microlaena stipoides in a south-eastern Australian pasture

Abstract. Microlaena (Microlaena stipoides var. stipoides (Labill.) R.Br.) is a C3 perennial grass that is native to areas of south-eastern Australia. In this region, perennial grasses are important for the grazing industries because of their extended growing season and persistence over several years. This series of experiments focused on the population biology of Microlaena by studying the phenology (when seed was set), seed rain (how much seed was produced and where it fell), seed germination, germinable seedbank, seed predation and seedling recruitment in a pasture. Experiments were conducted at Chiltern, in north-eastern Victoria, on an existing native grass pasture dominated by Microlaena. Seed yields were substantial (mean 800 seeds m–2), with seed rain occurring over December–May. Microlaena has two distinct periods of high seed rain, in early summer and in early autumn. Seed predation is high. Within a 24-h period during peak seed production, up to 30% of Microlaena seed was removed from a pasture, primarily by ants. Microlaena seedlings recruited throughout an open paddock; however, seedling density was low (5 seedlings m–2). Microlaena represented only low numbers in the seedbank (0.01–0.05% of total); hence, any seedlings of Microlaena that germinate from the seedbank would face immense competition from other species. Management strategies for Microlaena-dominant pastures need to focus on the maintenance of existing plants.

Summer drought survival and recovery in Microlaena stipoides

Microlaena stipoides (microlaena) is an important perennial grass in over 7 million hectares of native pastures in southern Australia and can survive and persist despite severe soil water deficits during summer. Many other pasture species survive similar conditions by relying on summer dormancy, which raises the possibility that microlaena may behave similarly. A field experiment using rainout shelters was conducted on an existing microlaena pasture in north-east Victoria. The experiment was a split-plot design with two watering treatments (‘summer storm’ or ‘summer dry’) as main plots and three defoliation treatments (nil, intense defoliation, strategic defoliation) as subplots. The ‘summer storm’ treatment resulted in the formation of new buds and tillers and increased basal cover from 1% in February to 18% in March. A glasshouse pot experiment examined the recovery of microlaena after different periods of drought and subsequent rewatering. In the pot experiment, microlaena withstood relatively short (up to 30 days) dry periods and then recovered when rewatered. Thus, it appears that microlaena is a persistent, perennial pasture plant that, although it survives very dry summers in Mediterranean areas, is not summer dormant. Microlaena does not exhibit summer dormancy in response to moisture stress and enter a quiescent stage, because normal growth is prevented by the lack of water, but it quickly recommences growth when soil water becomes available. The ability of microlaena to withstand summer soil water deficits and to recruit from seedlings make it a valuable pasture species across drought-prone environments, and this undoubtedly partly explains its very broad adaptation across eastern Australia.

Genetic diversity within a population of Microlaena stipoides, as revealed by AFLP markers

Microlaena stipoides (Labill.) R.Br. (microlaena), a C3 perennial grass, is common within grazed native pastures in the high-rainfall zone (>550 mm average annual rainfall) of south-eastern Australia. It has the ability to spread via seed production or vegetatively, using both rhizomes and stolons. This experiment aimed to determine how variable a microlaena population was within a single area, with the aim of determining whether microlaena relied on seed or vegetative spread to sustain populations. Leaf samples of microlaena were collected from 85 locations, sampling two transects, within a pasture at Chiltern, in north-eastern Victoria (36°12ʹS, 146°35ʹE). The genetic diversity among samples was analysed using amplified fragment length polymorphism (AFLP) markers. We obtained 1612 fragments, using 10 primers combinations. Polymorphism for the markers ranged from 47% to 65%. These results indicated that the populations of microlaena that exist within the pasture at Chiltern are likely to have undergone some degree of outcrossing (Fst = 0.0219). It is likely that recruitment is occurring from sexual reproduction as well as via clonal spread within the microlaena population examined. This ability to use vegetative spread as well as both sexual and asexual reproduction may make populations of microlaena more resilient in the longer term.

Climatic conditions for seedling recruitment within perennial grass swards in south-eastern Australia

Abstract. Recruitment of new perennial grass plants within existing grassland ecosystems is determined by seed availability, suitable microsites, nutrients and climatic conditions, water and temperatures. This paper reports on the development of criteria to predict recruitment events using modelled soil moisture conditions associated with recruitment of species in five field experiments at Orange (Phalaris aquatica), Trunkey Creek (Austrodanthonia spp.), and Wellington (Bothriochloa macra) in central New South Wales, Australia, and the frequency of those conditions during the past 30 years. Recruitment events were recorded when a rainfall event (median 68 mm across the three sites) kept the surface volumetric soil moisture (0–50 mm) above the permanent wilting point for at least 15 continuous days, allowing for, at most, two ‘dry days’ in between. A key finding from our study is that rainfall events creating favourable soil moisture conditions for seedling emergence typically occurred in the second half of February, sometimes extending to early March. Previously it was thought that recruitment would more likely occur through autumn, winter, and spring when rainfall in southern Australia is more reliable. The 30 years’ data (1975–2004) showed that the P. aquatica site had a median of 20 continuous moist days each year in February–March, whereas, there were 16 and 10 days for the Austrodanthonia and B. macra sites, respectively. The probabilities of exceeding seven or 15 continuous days of moist surface soil were 98% and 78% at the P. aquatica site, 91% and 49% at the Austrodanthonia site, and 73% and 30% at the B. macra site, and indicated that some recruitment is possible in most years. These analyses were extended to several sites across New South Wales, Victoria, and Tasmania to estimate the frequency with which recruitment could occur within natural swards. Across these sites, the probabilities of exceeding seven continuous days of soil moisture were >55% and of exceeding 15 continuous days were lower, which showed that suitable climatic conditions exist during late summer–early autumn across south-eastern Australia for a recruitment event to occur. Future research may show that the criteria developed in this paper could have wider regional application.