No abstract

To make effldent use of large germplasm collections, it is advisable to assemble a representative core collection and to evaluate the relationships among the traits studied. However, the assemblage of a core collection from very large germplasm collections is problematic. The computing resources needed to carry out genetic distance calculations and comparisons with commonly available programs is prohibitively large. The objects of this study were (i) to develop a method which assembles a core collection by maximizing the diversity (measured as mean Euclidean distance) from within groups of accessions defined by species, subspecies, and geographic origin and (ii) to test the effectiveness of the method on a collection of 20 997 annual Medicago accessions from the Australian Medicago Resource Center in Adelaide, South Australia, that had been evaluated for 27 agronomic characteristics. The method resulted in a core collection of 1705 accessions that represented 74% of the extremes of the 27 characters, indicating that the entire range of the characters was represented in most cases. Accessions representing the extremes easily could be added to the core collection. The method used requires relatively minor computing resources and should be useful to curators of large germplasm collections. To assess the relationships among the 27 measured traits, corrdation coefficients of all possible combinations of traits were calculated. The most strongly assodated traits were, as expected, such traits as grams of seed per plant and grams of pods per plant and indicated that some traits could be omitted from future evaluations with little loss of information, thereby increasing the efficiency with which germplasm evaluations can be carried ont.

Salinity tolerance is a complex trait inferring the orchestrated regulation of a large number of physiological and biochemical processes at various levels of plant structural organisation. It remains to be answered which mechanisms and processes are crucial for salt tolerance in lucerne (Medicago sativa L.). In this study, salinity effects on plant growth characteristics, pigment and nutrient composition, PSII photochemistry, leaf sap osmolality, changes in anatomical and electrophysiological characteristics of leaf mesophyll, and net ion fluxes in roots of several lucerne genotypes were analysed. Salinity levels ranged from 40 to ~200 mm NaCl, and were applied to either 2-month-old plants or to germinating seedlings for a period of between 4 and 12 weeks in a series of hydroponic, pot and field experiments. Overall, the results suggest that different lucerne genotypes employ at least two different mechanisms for salt tolerance. Sodium exclusion appeared to be the mechanism employed by at least one of the tolerant genotypes (Ameristand 801S). This cultivar had the lowest leaf thickness, as well as the lowest concentration of Na+ in the leaf tissue. The other tolerant genotype, L33, had much thicker leaves and almost twice the leaf Na+ concentration of Ameristand. Both cultivars showed much less depolarisation of leaf membrane potential than the sensitive cultivars and, thus, had better K+ retention ability in both root and leaf tissues. The implications of the above measurements for screening lucerne germplasm for salt tolerance are discussed.

Lucerne is a deep-rooted perennial forage legume with an important role in preventing dryland salinity in southern Australian cropping regions. Annual cereal production has created a water-use imbalance, which is placing the industry under threat through rising saline watertables and resultant dryland salinity. Lucerne is being incorporated into cropping systems to reduce groundwater recharge and improve the sustainability of grain production. Existing lucerne varieties have been developed for the animal industries, primarily for the areas with high rainfall or irrigation. The new challenge is to develop lucernes specifically for southern Australian cropping systems. This paper provides a background literature review of the breeding challenges that are anticipated in the development of these new types of lucerne. Lucerne is intolerant of acidic soils, waterlogging, saline soils, and intensive grazing. Other important attributes covered include the ability of the plant to fix nitrogen with existing rhizobia and be resistant to diseases that affect lucerne and other crops in the rotation. Finally, this paper addresses some of the breeding strategies that will be used to screen lucerne germplasm for tolerances to these soil conditions and diseases.

This paper describes the range in coumarin concentrations at 90% flowering stage in 149 accessions belonging to 15 Melilotus species grown in a genetic resources field characterisation experiment in Adelaide, South Australia, and determines coumarin concentrations in Melilotus species grown at two contrasting field sites in South Australia (Kybybolite and Keith). In the genetic resources characterisation experiment, the mean coumarin content ranged from 0.06 to 0.753% of dry matter. M. segetalis, M. dentatus, M. sulcatus, M. siculus and M. infestus recorded low (0.06 to 0.113%) coumarin levels while moderate levels (0.332Á0.753%) were registered in the other species. The coumarin levels at Kybybolite and Keith sites ranged from 0.095 to 0.943% amongst M. indicus accessions compared to M. siculus (0.007Á0.100%) and M. sulcatus (0.007Á0.810%). No coumarin was detected in a M. segetalis accession at these two sites. Accessions of M. siculus and an accession of M. segetalis (SA 36979) and of M. sulcatus (SA 40019) could be potential candidates as pasture legumes that can combine tolerance of both salinity and waterlogging, and acceptably low concentrations of coumarin.Keywords: Melilotus; coumarin; HPLC; flowering Introduction Species belonging to the genus Melilotus have recently received renewed attention for use in Australian farming systems due to the need for a broader range of leguminous species suitable for saline soils (Nichols et al. 2007; Dear & Ewing 2008). Melilotus albus Medik. has shown considerable potential (Evans & Kearney 2003) and recently the cultivar Jota was released (Evans and Thompson 2006). The potential of M. siculus (Turra) Vitman ex B. D. Jacks. (Syn M. messanensis) as a pasture species was also outlined by Nichols et al. (2008) and Rogers et al. (2008). When developing new pasture species it is important to know of the presence of secondary plant compounds, especially if there are animal health concerns associated with them (Revell & Revell 2007), if they affect feed intake or if they may cause tainting of food products. High concentrations of a secondary plant compound, coumarin, is a major limiting factor in the use of Melilotus species in Australia (Evans & Kearney 2003). Coumarin has been associated with dicoumarol production upon spoilage by fungi in M. albus (Poulton et al. 1980). Dicoumarol is an anticoagulant and high concentrations in forage or conserved fodder are undesirable for grazing animals (Stahmann et al. 1941). It is important to identify Melilotus species and genotypes with low coumarin levels. Vol. 53, No. 3, September 2010, 201Á213 The concentrations of secondary plant compounds are often variable, possibly because of their role in plant defence mechanisms to protect themselves from excessive herbivory, especially during the reproductive phase or in response to biotic or abiotic stressors. The work reported here was conducted with the objective of determining the variation in coumarin content in different species of Melilotus grown as part of a genetic resourc...