Soil salinity and drought severely affect all aspects of plant physiology, leading to significant losses of crop productivity and native biodiversity. A key to sustainable land use in such areas is to cultivate well-adapted native plants that are also commercially important and have the appropriate gene pool. Glycine betaine (GB) is an osmoprotectant that imparts salt and drought tolerance to some plants. It is also shown separately to provide significant health benefits to animals and humans. We investigated whether Australian saltbushes, which are extremely salt and drought tolerant and also impart health benefits to grazing animals, may have the genetic basis for GB biosynthesis, explaining the two different observations. Complementary DNAs encoding the two key enzymes of the plant GB biosynthesis pathway, choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), were identified and analysed from Atriplex nummularia and Atriplex semibaccata. The sequences showed the putative CMO proteins exhibited all functionally important features including the Reiske-type cluster (2Fe-2S) and mononuclear non-heme Fe cluster, and the putative BADHs exhibited conservation of active site residues. The expression of both genes was found to be significantly up-regulated in leaf tissues under salt stress. The leaf tissues also showed accumulation of very high levels of GB, at 29.69 mmol/kg fresh weight for A. nummularia and 42.68 mmol/kg fresh weight for A. semibaccata, which is several times higher than in cereal crops. The results demonstrate a strong potential of cultivation of saltbushes for re-vegetation and as a perennial fodder in salinity and drought-affected areas.
Use of saline lands for agroforestry relies primarily on plant species that have the trait of salinity tolerance, and also other economic and agronomic benefits. The selection of species, however, also needs to consider other key factors such as compatibility with existing flora, and potential for environmental benefits such as improved soil fertility or lowering of the water table in the case of dryland salinity. The testing of candidate species in particular environments needs substantial investments of costs and time. In this paper, a novel approach is presented for the rapid identification of potentially salt tolerant Acacia species, based on molecular phylogenetic analysis. The approach has been applied to four species groups, Acacia pendula, A. salicina, A. victoriae and A. stenophylla. The nuclear-encoded ribosomal DNA internal and external transcribed spacer (ITS and ETS) regions were used as markers, and phylogenetic analyses undertaken to identify closely related species that may share the salt tolerance traits. Such a methodology could be used to more rapidly identify candidate native species for agroforestry in salinity-affected regions and for preventing further expansion of salinity, thus assisting in biodiversity conservation.
The deleterious effects of soil salinity on biodiversity and agricultural productivity make it essential to devise strategies that would reduce its impact and expansion. For sustainable agriculture on dryland salinity affected areas, the use of native salt-tolerant plant species of economic value could provide a solution. In this work, the salinity tolerance potential of fifteen different Australian Acacia (wattle) species, pre-selected on the basis of phylogenetic relationships, were tested. The effects of salinity stress on morphological and physiological parameters, such as shoot and root lengths, shoot and root biomass, tissue water content, tolerance indices and accumulation of major cations (sodium, potassium, magnesium, calcium), all of which are indicators of salt stress response, were investigated. The species exhibited varied responses to the various parameters, some species consistently indicative of salt tolerance. Consolidating the tolerance indices based on morphological and physiological effects of salt stress, a method was developed to arbitrarily rank the species for their tolerance. Two highly tolerant, three tolerant and six moderately tolerant species could thus be identified. The work supports use of phylogenetics for initial screening for large genera, such as Acacia, and provides an experimental methodology for identification of candidate species for environmental stress tolerance and other applications.
In this paper, a novel approach for preliminary identification of salt tolerance in Acacia species is presented, based on molecular phylogenetic analysis using nuclear ribosomal DNA markers (ITS and ETS). Four species of Acacia, i.e., A. pendula, A. salicina, A. victoriae and A. stenophylla, had been initially identified as salt tolerant and were being used for a land reclamation project of a salinity degraded area in Victoria, Australia. Using molecular techniques, a phylogenetic tree was constructed to identify additional Acacia species closest to the four candidate salt tolerant species. These data could be potentially used to identify and select additional salt tolerant genotypes that can be used for land revegetation projects for salinity-affected areas. Since these species are native to Australian landscape, employing them in preventing the expansion of salinity will also help with biodiversity conservation.
The NSW Government commissioned catchment management boards (CMBs) to set the direction and process for catchment scale natural resource management. In the Lower Murray Darling, Rivers are highly regulated and water resources shared between three states. The Catchment Board only has jurisdiction over the northern bank of the Murray but salt and water enter the river from many locations upstream and along the area boundary. River salt and flow modelling has continually been improved to reflect and contribute to an increased understanding of salinity processes. The MDBC Salt Load study correlates 10 years of actual measured data with its modelled outputs, and estimates river salinities for 2020, 2050 and 2100. Routing models such as SALTFLO and MURKEY generate percentile salinity levels at different nodes in the River Murray downstream of the Lower Darling confluence. National, Murray-Darling Basin and NSW salinity management policy and legislative requirements were considered, MDBC model output was used to ensure the interim targets are achievable, auditable, and appropriate to the catchment. The method for an end-of-valley river based target for salinity is described. A target of less than 463 microS/cm for Lock 6, a point in the lower reaches of the Murray River is recommended for year 2010. Catchment management targets that express the main river salinity risk in five hydrologically distinct management zones are also recommended. Salinity management changes are needed in each zone to meet the end-of-valley target.
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