Sj Wilson

Multiple traits associated with salt tolerance in lucerne: revealing the underlying cellular mechanisms

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.

Incidence and type of cracking in sweet cherry (Prunus avium L.) are affected by genotype and season

Rain induced fruit cracking in sweet cherries takes 3 distinct forms: stem end cuticular fractures, calyx end cuticular fractures, and large cracks usually deep into the pulp on the cheek of the fruit. A 4-year study of sweet cherry varieties from a commercial orchard in Tasmania, Australia, was conducted to investigate the incidence of crack type and its relative likelihood, as influenced by both genotype and season. Although all 3 crack types developed in the 3-week period before commercial harvest, the extent of cracking was strongly controlled by season. While initial development of cracks coincided with rainfall, no relationship between amount of rain and incidence of cracking was found for crack type. A significant relationship was found between the tangential stress experienced by fruit skin from fruit at harvest maturity and the incidence of cracking recorded in the orchard. No other fruit property (pulp osmotic potential, fruit diameter, weight) explained the differences in incidence of cracking in the field between seasons or varieties. The results suggest that management of cracking needs to consider both varietal and seasonal factors. The development of turgor in maturing fruit also needs further investigation.

Challenging dominant discourses of climate change

The influence of language on communication about climate change is well recognised, but this understanding is under-utilised by those seeking to increase uptake of action for climate change. We discuss the terms, discourse, resistance, and agency, to assist in developing ways to progress social action for climate change. Using a review of academic literature about climate change, we explore three of the many dominant discourses that constrain action: the logical action discourse; the complexity discourse; and the culture of consumption discourse. While there are more discourses about climate change, especially in the popular literature, the ways these three operate in the peri-scientific sphere is under-recognised. We suggest that by examining the different framings of climate change, there is potential to create novel discourses and to start new processes of societal response. This paper challenges the dominant scientific framing of climate change and seeks to begin the process of creating change through changing discourses.

Water relations in Eucalyptus regnans nursery plants following root exposure after lifting.

Water relations of Eucalyptus regnans seedlings during root exposure and associated desiccation were studied in three trials. In the first, changes in water potential and relative water content (RWC) of leaves and hydraulic resistance in the lower stem were recorded during exposure. In the two subsequent trials, different exposure conditions resulted in different rates of desiccation. After various exposure times, roots were soaked for 24 h in aerated distilled water under continuous light before measuring root and whole plant hydraulic resistance. Exposure for 5-8 h and accompanying short term leaf water stress to below -2 MPa resulted in significant increases in hydraulic resistance of stem, roots and whole plant. Although leaf water potentials at the longest exposure times in one trial fell below the probable turgor loss point, there was no apparent permanent leaf damage. In the two trials in which roots were soaked before hydraulic resistances were measured, there was a marked difference in the response of leaf water potential to soaking. Although hydraulic resistance increased with longer exposure in both trials, the results from one trial suggested a further increase during soaking. Differences between the two trials suggested differences between plants before treatment or the soaking treatment itself may also have influenced water relations after exposure. Results are discussed in terms of the practical implications, particularly effects of nursery management on the condition of trees at lifting and subsequent water relations of lifted seedlings during and after transplanting. Some aspects of regulation of water stress by E. regnans seedlings are also discussed.

Nursery factors influencing lateral shoot development in a spur type apple cultivar

Abstract The effects of budding height and in-row spacing on lateral bud growth in a spur bearing red ‘Delicious’ strain budded onto MM106 rootstocks are reported. Results show that branching is suppressed at close in-row spacing and the proportion of branched trees, number and length of branches all increase at wider spacings with no change in tree height. There was a positive relationship between stock size and both the proportion of trees which branched and branch length. Budding height did not influence either branch or total growth with height of first branch above the graft union remaining constant. It is concluded that while the use of wider in-row spacing and larger stocks will improve branching, practical application of the results is limited by high variability and increased costs of production.

A statistical model to estimate bud fruitfulness in Pinot noir

A statistical model to estimate and describe bud fruitfulness in Pinot noir in cool environments was developed. The study compared Pinor noir fruitfulness at three different sites during winter dormancy by light microscopy and actual fruitfulness established three weeks after budburst. Strong differences were observed between inflorescence primordia counts and actual inflorescence number after budburst. When examined microscopically, fruitfulness was evenly distributed along the cane with the exception of the first two nodes, which were significantly lower. In contrast, actual fruitfulness after budburst showed site differences and interactions between fruitfulness and node position. Cane starch was a significant predictor for inflorescence count.

Effect of frost damage and pruning on current crop and return crop of Pinot Noir

Abstract In October 2006, much of the wine-growing area in Tasmania was affected by a series of some of the worst frost events in more than 30 years. Widespread damage left vineyards with blackened shoots and the prospect of a considerably smaller crop, with later maturing bunches from secondary buds contributing to poorer quality wine. In a commercial, spur-pruned Pinot Noir planting, treatments intended to encourage and manipulate secondary bud-burst are imposed and effects on yield recorded. Treatments are imposed 10 days after the frost and include: (i) an untreated control (control) with all damaged tissue left in place; (ii) frost-damaged tissue removed (light pruning); (iii) frost-damaged tissue removed and original spur trimmed back to one bud (medium pruning); and (iv) original (damaged) shoot removed back to compound bud on the spur (heavy pruning). Pruning treatment responses for season 2006–07 show that heavy pruning reduces the current crop with no useful gain in uniformity of ripening. The medium and heavy pruning treatments also reduce pruning weights at the end of the season and all post-frost pruning treatments result in a smaller inflorescence primordia size in dormant buds dissected at the beginning of commercial pruning. In the 2007–08 vintage, the untreated control and the medium pruning treatment have significantly lower bunch numbers than the other treatments. There is also a significant effect of terrain elevation on total yield and the number of bunches in the frost year, with increasing damage lower in the inversion. This gradation in damage does not have carry-over effects into the second season. The results indicate that none of the pruning treatments tested have clear benefits for current or subsequent season production, and that a prescriptive approach to pruning should be avoided when the level of frost damage is inconsistent across vines.