Influence of leaf area density and trellis/training system on the light microclimate within grapevine canopies

The influence of leaf area density and canopy configuration on the light microclimate within 6 wine grape trellis/ training systems commonly used in California (single curtain, double curtain, vertically shoot positioned, lyre, Smart-Henry and Smart-Dyson) was examined in two experimental vineyards (Oakville and Parlier). Mean canopy leaf area density varied considerably among the systems, ranging from approximately 2.8 m2m-3 for the Wye to 10.1 m2m-3 for the VSP. Non-positioned systems were characterized by a layer of relatively high leaf area density in their outer envelope and lower leaf area densities in their interior. In contrast, leaf area density in positioned systems increased from the top of the canopy moving downward to the fruit zone. Mean leaf area density within the fruit zone ranged from near 6 m2m-3 in the DC to over 12 m2m-3 in the VSP and LYR. The pattern of light attenuation within the canopy was generally similar among the systems, with PPF reaching its lowest level in or near the fruit zone. Fruit zone PPF was >10 % of ambient sunlight in low density canopies and <5 % in high density canopies. A gradual decline in fruit zone PPF was found as leaf area density increased in positioned systems. PPF decreased sharply in the fruit zone of non-positioned systems as leaf area density increased from 2 to 4 m2m-3, then leveled as leaf area density exceeded 6 m2m-3. Fruit zone PPF decreased as the leaf area density of divided systems increased from 2 to 4 m2m-3, then declined gradually as leaf area density approached 6 m2m-3. Fruit zone PPF in non-divided systems was initially lower, and declined more gradually as leaf area density increased, compared to divided systems. Compared to positioned systems, leaf layer number in the fruit zone rose more sharply in non-positioned systems as leaf area density increased. Leaf layer number was greater in nondivided systems compared to divided systems, but declined at similar rates in both systems as leaf area density increased. Shoot-positioned systems achieved well-exposed fruit zones at higher leaf area densities, but lower leaf layer numbers, compared to non-positioned canopies

Colour assessment outcomes – a new approach to grading the severity of color vision loss

INTRODUCTION: Recent studies have shown that a significant percentage of subjects with anomalous, congenital trichromacy can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats. In the absence of detailed, occupation-specific studies, an alternative approach is to make use of new findings and the statistical outcomes of past practices that have been considered safe to produce graded, justifiable categories of colour vision that can be enforced. METHODS: We analyzed traditional color assessment outcomes and measured severity of colour vision loss using the CAD test in 1363 subjects (336 normals, 705 deutan, 319 protan and 3 tritan). The severity of colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. RESULTS: The correlation between the number of Ishihara (IH) test plates subjects fail and the severity of RG colour vision loss was very poor. The 38 plates IH test has high sensitivity when no errors are allowed (i.e., only 0.71% deutans and 0.63% protans pass). Protocols based on zero errors are uncommon since 18.15% of normal trichromats fail. The most common protocols employ either the 24 or the 14 plates editions with two or less errors. These protocols pass almost all normal trichromats, but the deutans and some protans that also pass (when two or less errors are allowed) can be severely deficient. This is simply because the most challenging plates have not been included in the 24 and 14 plates editions. As a result, normals no longer fail, but the deutans and protans that pass have more severe loss of colour vision since they fail less challenging plates. The severity of colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. DISCUSSION: Historical evidence and new findings that relate severity of loss to the effective use of colour signals in a number of tasks provide the basis for a new colour grading system based on six categories. A single colour assessment test is needed to establish the applicant’s Colour Vision category which can range from ‘supernormal’ (CV0), for the most stringent, colour-demanding tasks, to ‘severe colour deficiency’, when red / green colour vision is either absent or extremely weak (CV5)

Chilling requirements and dormancy evolution in grapevine buds.

Fluctuations in winter chilling availability impact bud dormancy and budburst. The objective of this work was to determine chilling requirements to induce and overcome endodormancy (dormancy controlled by chilling) of buds in different grape cultivars. "Chardonnay", "Merlot" and "Cabernet Sauvignon" shoots were collected in Veranópolis-RS vineyards in 2010, and submitted to a constant 3 °C temperature or daily cycles of 3/15 °C for 12/12h or 18/6h, until reaching 1120 chilling hours (CH, sum of hours with temperature ≤ 7.2 °C). Periodically, part of the samples in each treatment was transferred to 25 °C for budburst evaluation (green tip). Chilling requirements to induce and overcome endodormancy vary among cultivars, reaching a total of 136 CH for "Chardonnay", 298 CH for "Merlot" and 392 CH for "Cabernet Sauvignon". Of these, approximately 39, 53 and 91 CH are required for induction of endodormancy in the three cultivars, respectively. The thermal regimes tested (constant or alternating) do not influence the response pattern of each cultivar to cold, with 15 °C being inert in the CH accumulation process. In addition, time required to start budburst reduces with the increase in CH, at a rate of one day per 62 CH, without significant impacts on budburst uniformity. Index terms: Chilling hours; endodormancy; budburst; Vitis vinifera

Leaf water potential and sap flow as indicators of water stress in Crimson ‘seedless’ grapevines under different irrigation strategies

Vitis vinifera L. cv. Crimson Seedless is a late season red table grape developed in 1989, with a high market value and increasingly cultivated under protected environments to extend the availability of seedless table grapes into the late fall. The purpose of this work was to evaluate leaf water potential and sap flow as indicators of water stress in Crimson Seedless vines under standard and reduced irrigation strategy, consisting of 70 % of the standard irrigation depth. Additionally, two sub-treatments were applied, consisting of normal irrigation throughout the growing season and a short irrigation induced stress period between veraison and harvest. Leaf water potential measurements coherently signaled crop-available water variations caused by different irrigation treatments, suggesting that this plant-based method can be reliably used to identify water-stress conditions. The use of sap flow density data to establish a ratio based on a reference ‘well irrigated vine’ and less irrigated vines can potentially be used to signal differences in the transpiration rates, which may be suitable for improving irrigation management strategies while preventing undesirable levels of water stress. Although all four irrigation strategies resulted in the production of quality table grapes, significant differences (p ≤ 0.05) were found in both berry weight and sugar content between the standard irrigation and reduced irrigation treatments. Reduced irrigation increased slightly the average berry size as well as sugar content and technical maturity index. The 2-week irrigation stress period had a negative effect on these parameters