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.

& Context High temperature stress in nurseries germinating Eucalyptus globulus seed is an important problem affecting germination synchrony and rate. Where there is a risk of hightemperature stress, then the choice of female parent may be important. This issue is particularly relevant to the production of full-sib families from mass-supplementary pollination where there may be opportunities for seed producers to manipulate the directionality of the crossing done in seed orchards.& Aims This study aimed to quantify the maternal versus paternal influence of seed sensitivity to high temperature stress during germination. & Methods A diallel crossing scheme involving four genotypes was used to test the relative importance of male and female genetic influences on the germination and development of E. globulus seed and their response to high temperature stress. Seed was germinated at optimum (25°C) and supra-optimal (32°C and 37°C) temperatures, and six traits

Abstract& Key message The maternal genotype has a significant effect on most germination traits of Eucalyptus globulus seeds. These differences can be partly explained by genetic-based differences amongst races, including differences in sensitivity to high temperatures which may be of adaptive significance. & Context Slow and uneven germination of Eucalyptus globulus seeds in commercial nurseries can be a problem which has been linked with periods of high temperature. & Aims This study aimed to determine whether maternal genotype affects the germination of E. globulus seeds.& Methods By sampling seeds over two seasons from multiple randomised ramets (trees) of maternal genotypes from three races of E. globulus growing in a seed orchard, the extent of genetic control of seed germination responses was assessed at different germination temperatures. & Results Maternal genotype had a significant effect on most germination traits but a differential response to temperature was more evident for germination proportion than rate traits. Maternal races differed in their rate of seedling development regardless of temperature, but differences in the germination proportion were only detected at high temperatures. & Conclusion The present study highlights the potential adaptive significance of the germination response and the need for seed lot-specific germination testing as both genetics and maternal environment vary.

Low capsule set is a major factor limiting the productivity of Eucalyptus globulus seed orchards. This study tested the effect of flower density, as well as two common irrigation techniques on capsule and seed set. Ramets with high flower density had significantly lower capsule set (69.7%) than those with low flower density (81.7%). In a regulated deficit irrigation trial, the non-irrigated ramets set a higher proportion of capsules (63.6%) than the ramets that received conventional irrigation (CI) (51.4%). In a partial root zone drying (PRD) trial, capsule set was highest in the absence of irrigation (74.7%) followed by the PRD treatment (67.8%) and then CI (53.7%). The CI treatment tended to produce the highest number of seed per capsule. Increased water availability resulted in increased vegetative growth, which was associated with higher levels of abortion in developing capsules but those surviving tended to have higher seed set. It is argued that the observed effects of irrigation and flower density can be explained by resource competition between vegetative and reproductive growth as well as competition among reproductive structures themselves.