Potassium and magnesium mediate the light and co2 photosynthetic responses of grapevines

Potassium (K) and magnesium (Mg) deficiency are common stresses that can impact on grape yield and quality, but their effects on photosynthesis have received little attention. Understanding the diffusional and biochemical limitations to photosynthetic constraints will help to guide improvements in cultural practices. Accordingly, the photosynthetic response of Vitis vinifera cvs. Shiraz and Chardonnay to K or Mg deficiency was assessed under hydroponic conditions using miniature low-nutrient-reserve vines. Photosynthesis was at least partly reduced by a decline in stomatal conductance. Light and CO2-saturated photosynthesis, maximum rate of ribulose 1.5 bisphospate (RuBP) carboxylation (Vcmax) and maximum rate of electron transport (Jmax) all decreased under K and Mg deficiency. Likewise, chlorophyll fluorescence and electron transport were lower under both nutrient deficiencies while dark respiration increased. K deficiency drastically reduced shoot biomass in both cultivars, while root biomass was greatly reduced under both Mg and K deficiency. Taken together, these results indicate that the decrease in biomass was likely due to both stomatal and biochemical limitations in photosynthesis. Optimising photosynthesis through adequate nutrition will thus support increases in biomass with carry-on positive effects on crop yields

Identifying individual nutrient deficiencies of grapevine leaves using hyperspectral imaging

The efficiency of a vineyard management system is directly related to the effective management of nutritional disorders, which significantly downgrades vine growth, crop yield and wine quality. To detect nutritional disorders, we successfully extracted a wide range of features using hyperspectral (HS) images to identify healthy and individual nutrient deficiencies of grapevine leaves. Features such as mean reflectance, mean first derivative reflectance, variation index, mean spectral ratio, normalised difference vegetation index (NDVI) and standard deviation (SD) were employed at various stages in the ultraviolet (UV), visible (VIS) and near-infrared (N.I.R.) regions for our experiment. Leaves were examined visually in the laboratory and grouped as either healthy (i.e. control) or unhealthy. Then, the features of the leaves were extracted from these two groups. In a second experiment, features of individual nutrient-deficient leaves (e.g., N, K and Mg) were also analysed and compared with those of control leaves. Furthermore, a customised support vector machine (SVM) was used to demonstrate that these features can be utilised with a high degree of effectiveness to identify unhealthy samples and not only to distinguish from control and nutrient deficient but also to identify individual nutrient defects. Therefore, the proposed work corroborated that HS imaging has excellent potential to analyse features based on healthiness and individual nutrient deficiencies of grapevine leaves

Grapevine reproductive performance: the role of amines, and the effects of salt and silicon.

Optimising reproductive performance of the grapevine is one of the major difficulties faced by Australian viticulturists due to a physically and economically challenging environment. It is well-documented that salt stress is one of the challenges that causes significant damage to grapevine vegetative and reproductive performance. One of this project’s aims was to investigate the yield reduction caused by salt stress during and post flowering. While the ability of silicon (Si) to enhance salt tolerance and yield performance is well-known in many crops especially cereals, the use of Si as a tool for improving grapevine reproduction under saline conditions is inconclusive. This study demonstrated that salt stress reduces fruit set by increasing flower abscission and interrupting normal berry development, which results in more live green ovaries and seedless berries in a bunch. The poor berry development due to impaired fertilization correlated with poor pollen tube growth in the style, while pollen viability and stigma receptivity were not affected by salinity. A significantly higher amount of Na⁺ and Cl⁻ was found both in leaves and flowers after salt treatment and was not affected by additional Si application. The inability of Si to restrict Na⁺ and Cl⁻ ions in the reproductive organs of grapevines correlated with its inability to ameliorate the deleterious effects of salinity on the reproductive performance of grapevines. However, this study identified the possible role of Si in improving water use efficiency of non-stressed vines. Bioactive amines are a group of growth regulators which are reported to have major roles in many aspects of grapevine reproductive development as well as stress tolerance. The reproductive performance of three red winegrape cultivars commonly used in Australian viticulture; Shiraz, Cabernet Sauvignon and Merlot were investigated in relation to the occurrence of different amines in the reproductive organs. Amine profiles of the flowers and developing berries significantly differed among these three cultivars. Significantly higher amounts of diaminopropane (DAP) were found in Merlot and Cabernet Sauvignon and correlated with a higher proportion of underdeveloped berries. An aromatic amine phenylethylamine (PEA) not previously reported for grapevine was found to be the major free amine in the flowers of Merlot, which is a cultivar susceptible to poor fruit set. To the best of our knowledge, this is the first study to indicate that PEA may have a role in the reproductive performance of grapevines. Exogenous application of amines was also investigated as a way to manipulate the endogenous levels of each targeted amine and to manipulate fruit set. Results from this investigation were inconclusive and as such further studies are required to determine the concentration and timing of application that have an effect on different cultivars. To undertake controlled environmental experiments small fruiting grapevines were used; we further developed a method described by Mullins and Rajasekaran (1981) into a technique designed to obtain optimal growth in controlled conditions to produce experimental grapevine plants with optimal nutrition and adequate and consistent reproductive performance. This research led to significant advances in our understanding of grapevine reproductive biology, the impact that salt stress has upon flowering, fruit set and ultimately yield, and the involvement of amines in the reproductive performance of grapevines. Based on these results new research avenues are proposed to further our understanding.Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 201

Acta Hortic.

Optimisation of nitrogen (N) supply and other nutrients in vineyards is critical to quality and quantity of fruit and wine production. However, there are major challenges to balance N availability for canopy growth in spring, reproductive development, fruit maturity rates and optimum grape composition at harvest. Therefore, frequent monitoring of nutrient status is essential to better predict and target inputs and consequentially maximise profitability. Rapid and convenient assessment of grapevine N status in the field can help identify N requirements during the season. A replicated experiment was undertaken in a glasshouse using two-year-old ‘Shiraz’ vines from dormancy to veraison that were pruned back to four two-bud spurs. The vines were previously water stressed, re-potted in washed river sand and then placed into a cool room at approximately 5-6°C for 14 days. From the end of dormancy, different nutrient solutions were applied to create a range of leaf nutrient levels for N, supplying approximately 100, 50 and 0% of N required for the bud burst to veraison period. Spectrometer measurements (reflectance) and leaf samplings were conducted at three times (at flowering, four weeks before and after) and three locations along the shoots (opposite the basal bunch, and two and four nodes above the basal bunch). The leaves were washed, separated into blades and petioles, ground and analysed for N concentration. The reflectance, particularly around 550 nm, showed considerable difference between N treatments, and these were more pronounced on the older leaves and later in the season. Leaf and petiole N concentrations were closely related, allowing the calibration of the indirect measurements with a spectrometer to establish petiole standards for flowering. Better understanding of changes in leaf N concentrations during vine development will allow for more accurate predictions of N requirements throughout the growing season

Differential accumulation of potassium in the vegetative and reproductive organs of three grapevine cultivars

Vine nutrition and vineyard fertilizer management have long-term implications for plant performance, notably vigour, crop load and fruit composition. Grape and wine composition is intrinsically linked to vineyard management practises. Wine sensory outcomes such as flavour, colour and aroma are heavily dependent upon intrinsic grape properties including pH, which in turn is influenced by berry potassium (K) concentration. Cultivar differences in the accumulation of nutrients is evident, however, tracking the accumulation of K in the various vine tissues is crucial for understanding how this macronutrient should be monitored during the season to achieve optimum growth performance and grape quality. We studied three economically important wine grape cultivars in Australia, grown under identical conditions, to determine how K accumulation differs between the cultivars, between the vegetative and reproductive organs and between two node positions on the shoot. The samples were collected at flowering and veraison and analysed for K by inductively coupled plasma atomic emission spectroscopy (ICP-AES). K concentrations ([K]) increased or decreased between these two phenological stages depending on cultivar, organ and node position. [K] in the berry and flower were not correlated with [K] in the leaf blade, petiole, or bunch stem. The differential accumulation of K in various organs points towards complex partitioning and mobilisation patterns, and this will have implications for berry pH and acidity at harvest. The differential accumulation of K between cultivars suggests that cultivar specific reference standards are required

Characterising leaf petiole, blade and bunchstem nutrient concentration across three grapevine cultivars

Background and Aims: Tissue nutrient concentration is useful for determining vine nutritional status and managing vineyard nutrition. Current Australian guidelines are based on the analysis of petioles at flowering and leaf blades at veraison, sampled adjacent to the basal inflorescence and bunch. The comparative value of these two tissue types and that of the bunchstem for assessing plant nutrient status at the two phenological stages is required. Moreover, the impact of node position and cultivar is unclear. Methods and Results: We characterised the macro and micronutrients at flowering and veraison of three segments of the petiole, the entire leaf blade and the bunchstem at two node positions of cvs Cabernet Sauvignon, Shiraz and Chardonnay grown under identical conditions. Nutrient concentration was non-uniform along the length of the petiole. The middle segment had the lowest concentration of most macronutrients, while Mn was generally highest in the middle segment. When averaged across petioles, blades and bunchstems the lower node had a higher nutrient concentration than the upper node, except for K. The concentration of some nutrients within the leaf blade was correlated with those of the petiole but this was dependent on the cultivar and the time of sampling. The nutrient concentration of the bunchstem was more closely correlated to the petiole than to the blade. Cultivar differences were also apparent, but this depended on the individual nutrient and the sampling time. Conclusions: Nutrient concentration was inconsistent along the length of the petiole. The nutrient concentration of petioles, blades and bunchstems was node, cultivar and time specific. Therefore, tissue nutrient analysis will be meaningful only if sampling is consistent across these variables. Significance of the Study: These results will aid in the formation of better sampling protocols for accurate grapevine nutrient diagnosis