Grapevine Vegetative Growth Research Articles

Effect of PGR on Growth and Establishment of Grapes (Vitis vinifera L.) cv. Thompson Seedless under Prayagraj Agro Climatic Condition

Grapes (Vitis vinifera) is one of the important commercial subtropical crops, which is a good source of vitamins and minerals. It is grown throughout the world except the places with extreme temperature and high altitude .So, to find out Effect of PGR on growth and establishment of grapes cv. Thompson Seedless under Prayagraj agro climatic condition; a field experiment was conducted at Horticulture Research Farm, Department of Horticulture, Naini Agriculture Institute, Sam higginbottom University of Agriculture, Technology and Science, Prayagraj, U.P-211007 during the year 2022. The experiment comprised of 10 different treatment of three different plant growth regulator comprising of GA3, IAA and IBA with different concentration of 50 ppm, 100 ppm and 150 ppm; 100 ppm, 300 ppm and 500 ppm; 1000 ppm, 2000 ppm and 3000 ppm respectively. The main objective of the experiment was to evaluate the root and vegetative growth of grapevines with their success and survival in the Prayagraj agro-climatic zone. From the present investigation, treatment T9 (IBA @3000 ppm) was found best with least days to emerge from the bud from the grapes cutting (6.4 days) with maximum amount of sprouting percentage (77.7%). It also showed the best root growth parameters with maximum root length 25.1cm @120DAP and maximum number of roots per cutting 49.3 @120DAP. It also showed best vegetative growth parameters with maximum shoot length 13.4cm @120DAP, maximum stem diameter 28.1mm @120DAP, highest number of leaves with 12.5 @120 DAP, maximum leaf area 73.9cm2, maximum plant height after transplanting 14.9cm and highest survival percentage 88.8% of grapes plant. The T9 showed the best results with all major parameters when cuttings were treated with different concentrations of plant growth regulators.

Cover crops and a devigorating rootstock can impart substantial agroecosystem services to high-resource vineyards: A multi-year study

In vineyards, cover crops typically grow concurrently with grapevines and can impart a multitude of agroecosystem services; yet concerns over potential disservices might limit adoption. Reductions in yield and vegetative growth are key disservices of concern, but at sites with high soil resources, reducing excessive vegetative growth is often considered beneficial, if the yield is not strongly penalized. To optimize agroecosystem services provided by cover crops, it is crucial to examine above- and belowground plant responses over multiple years. Documentation of the responses of fruit crop root systems to cover crops may clarify potential benefits for long-term agroecosystem services associated with aboveground growth and soil resources. In 2016, we established a perennial grass under young vines (full floor cover) to examine if agroecosystem services imparted by an under-vine cover crop change in the first five years of vineyard production and depend on rootstock vigor. Overall, cover crop reduced grapevine vegetative growth between 13% and 30% across all years and with a trend of more substantial reductions in the first two years. In contrast, yield was reduced in only three of the five years, between 9% and 25%, depending on the rootstock. Furthermore, neither cover crop nor differences in rootstock vigor resulted in relevant or consistent changes in fruit chemistry during the study. Overall, we found that in a relatively fertile, young vineyard, combining a lower vigor rootstock with a perennial, under-vine cover crop imparts substantial agroecosystem services in comparison to the more common practices of using a medium vigor rootstock and spraying herbicide under the vines. These services included improved crop load (ratio of fruit to vegetative mass), increased soil phosphorus availability, increased deep soil water content, and presumably lower labor and other costs associated with vineyard maintenance. Studies on a decadal timescale are needed to further clarify whether these services persist, accumulate with time, or if competition from the cover crop eventually leads to unacceptable decreases in vine nutrient status, growth, and production.

Biostimulation can prime elicitor induced resistance of grapevine leaves to downy mildew.

Using plant defense elicitors to protect crops against diseases is an attractive strategy to reduce chemical pesticide use. However, development of elicitors remains limited because of variable effectiveness in the field. In contrast to fungicides that directly target pathogens, elicitors activate plant immunity, which depends on plant physiological status. Other products, the biostimulants, can improve certain functions of plants. In this study, the objective was to determine whether a biostimulant via effects on grapevine physiology could increase effectiveness of a defense elicitor. A new methodology was developed to study biostimulant activity under controlled conditions using in vitro plantlets. Both biostimulant and defense elicitor used in the study were plant extracts. When added to the culture medium, the biostimulant accelerated the beginning of plantlet growth and affected the shoot and root development. It also modified metabolomes and phytohormone contents of leaves, stems, and roots. When applied on shoots, the defense elicitor changed metabolite and phytohormone contents, but effects were different depending on whether plantlets were biostimulated or controls. Defense responses and protection against Plasmopara viticola (downy mildew agent) were induced only for plantlets previously treated with the biostimulant, Therefore, the biostimulant may act by priming the defense elicitor action. In this study, a new method to screen biostimulants active on grapevine vegetative growth was used to demonstrate that a biostimulant can optimize the efficiency of a plant defense elicitor.

Use of Under-Vine Living Mulches to Control Noxious Weeds in Irrigated Mediterranean Vineyards.

This article assesses the use of under-vine living mulches in Mediterranean vineyards characterized by limited water resources, one of the reasons why this agronomic practice is currently unusual in these environments. The aim of the study was to test whether the use of this alternative method in Mediterranean vineyards could suppress noxious weeds without hindering optimal vineyard development. For this purpose, four native species were selected as living mulches: Festuca ovina, Pilosella officinarum, Plantago coronopus, and Plantago lanceolata. The variables measured during three years in two different experimental farms were: (a) living mulch cover, as a possible predictor of weed suppression success; (b) weed density and weed biomass, with special attention to noxious weed species; and (c) pruning weights, measured in the last year to analyze the cumulative effect of the treatments on the grapevine vegetative growth. Our results revealed that living mulches with high cover rates (average over 70%) also showed weed suppression of up to 95%, significantly controlling the occurrence of noxious weeds such as Erigeron canadensis. No significant effect of the different treatments on vine vegetative growth was found, although further studies would be necessary. Based on these findings, it can be concluded that under-vine living mulches could be an efficient and environmentally friendly method for weed control in Mediterranean vineyards where irrigation is available.

Aerial images to monitor grapevine vegetative growth

Images obtained by Remotely Piloted Aircraft (RPA) used to monitor the crop can help evaluate leaf mass, plant formation, and plant population. In this context, the objectives of this study were to analyze plant growth in a grapevine crop trained in the trellis system, detect failures and determine the plant covered area using images obtained by RPA. The flight was parameterized with frontal overlap of 75%, lateral overlap of 70%, Ground Sample Distance (GSD) of 60 m, and flight speed of 5 m.s-1, using a sensor in the visible range. Processed images showed a stand 3% smaller than projected, an area covered by vine branches occupying 60.8%, undergrowth and invasives represented 5.3%, and exposed soil 33.9%. Vines were identified in the vegetation indices as green points, invasive plants as yellow points, and exposed soil as red points. Image processing obtained with RPA allowed identification of plants in various stages of development, with predominance of vines in the formation process. It was possible to identify the plants and quantify the leaf mass using the MPRI vegetation index, as well as to differentiate exposed soil from plant material. It was also observed that the plot had an incomplete stand at the time the flight was performed.

Vineyard establishment under exacerbated summer stress: effects of mycorrhization on rootstock agronomical parameters, leaf element composition and root-associated bacterial microbiota

AimsClimate change imposes adaptation of viticulture in risk areas, such as the Mediterranean. Mycorrhization is a valid tool to reduce the impact of the expected temperature/drought increase. Aim of this work was to test the effects of mycorrhization on grapevine vegetative growth, element composition of soil/leaves, and microbiota of bulk soil/rhizosphere/endorhiza, in the field, under exacerbated summer stress conditions obtained by planting the rootstocks in June.Methods118 rooted cuttings of 1103-Paulsen (Vitis berlandieri × Vitis rupestris) were planted in Salento (Apulia, Southern Italy); about half of them were mycorrhized. Leaf Area Index, shoot growth and survival rate were monitored across two growing seasons. Leaf/shoot weight, chemical analysis of 25 elements, and 16S rRNA gene metabarcoding of bulk soil/rhizosphere/endorhiza were performed on subsamples.ResultsMycorrhized plants showed significantly higher survival rate and growth, and accumulated significantly higher amounts of 18 elements. 27 endorhizal OTUs (representing ~20% of total sequences) were differently distributed (20 OTUs more abundant in mycorrhized plants); in the rhizosphere, instead, 12 OTUs (~2.5% of total sequences) were differently distributed. A few Actinobacterial OTUs were enriched by mycorrhization in the root endosphere; the same OTUs were the most correlated with the chemical elements, suggesting a role in element dynamics. These OTUs were not hub taxa of the co-occurrence network.ConclusionsThis work shed light onto the interactions between mycorrhiza and microbiome, in the context of plant element dynamics, which is useful to identify potential target candidates for biotechnological applications, thus moving towards a more sustainable, ecosystem-based viticulture.

Arbuscular Mycrorrhizal Fungi Inoculation and Applied Water Amounts Modulate the Response of Young Grapevines to Mild Water Stress in a Hyper-Arid Season.

Several factors may affect the success of a replanting vineyard. Given the current environmental conditions, an optimized irrigation schedule would still be one of the most desirable tools to improve crop productivity and fruit quality. On the other hand, the symbiosis of grapevines with arbuscular mycorrhizal fungi (AMF) is a key component of the vineyard production systems improving the vine growth, nutrient uptake, and berry quality. The aim of this study was to characterize the response of Merlot grapevines to AMF inoculation and two different irrigation amounts in their first productive year. The experiment was conducted on 2-year Merlot grapevines inoculated with AMF (I) or not-inoculated (NI) and subjected to two irrigation amounts, full irrigated (FI), where the amount of water was enough to maintain expansive growth and half irrigated (HI) where plants received the half of the amount of water of FI plants. Water status, gas exchange parameters, growth, mineral content, berry composition, and mycorrhizal colonization were monitored through the season. AMF inoculation improved the grapevine vegetative growth, water status, and photosynthetic activity, especially when vines were subjected to HI irrigation; however, no effect was observed on the leaf mineral content, must pH, total soluble solids, or total acidity. The main effects were observed on the flavonoid composition of berry skins at harvest. Irrigation amounts and mycorrhizal inoculation modified cyanidin and peonidin derivatives whereas flavonol composition was mainly affected by irrigation treatments. A strong relationship between the mycorrhizal colonization rate of roots and total quercetins, cyanidins, and peonidins was found. Findings support the use of a mycorrhizal inoculum and a better water management in a hyper-arid growing season; however, these results may be affected by edaphoclimatic characteristics and living microbiota in vineyard soils, which should be taken into account before making the decision of inoculating the vineyard.

Vigor thresholded NDVI is a key early risk indicator of Botrytis bunch rot in vineyards

Botrytis bunch rot (BBR) is a major disease occurring in vineyards worldwide. Its control is still largely based on the use of synthetic fungicide sprayings at predetermined intervals, which often produces negative residues in grapes and wines that may affect the environment and/or human health. To rationalize BBR management, disease risk indicators were developed and evaluated in a set of field experiments carried out between 2010 and 2019 in France and Chile. Key indicators include early grapevine vegetative growth, i.e. ground-based normalized difference vegetation index (NDVI), and the potential berry susceptibility to Botrytis cinerea, which is driven by tannin content in the skin. Under these contrasting weather and cropping conditions, regression analyses, including weather information, showed a highly significant positive correlation between the early NDVI, measured at berry pea size stage, and BBR incidence or severity at harvest, whereas the opposite was demonstrated for tannin content in the berry skin measured at an early herbaceous fruit stage. The exponential relationship between the final disease severity and the early NDVI allowed us to identify a possible threshold NDVI value, i.e. between 0.5 and 0.6, under which the BBR severity should be lower or close to 5% at harvest (BBR tolerance threshold for wine quality).

Complete vineyard floor cover crop to reduce grapevine susceptibility to bunch rot

Abstract Excessive vine growth not only negatively impacts fruit composition but also fosters bunch rot incidence. The goal of our study was to improve Vitis vinifera (Tannat) grape and wine composition and decrease bunch rot incidence by achieving adequate vine vegetative growth in a humid climate. Our approach was to use under-trellis cover crops (UTCC) to limit vine water availability and reduce excessive vine growth. We tested UTCC consisting of full cover of the vineyard soil with red fescue (Festuca rubra) versus conventional alleyway red fescue with 1.0 m wide weed-free strips under the trellis (H). As excessive competition with grapevines remains the main reason for UTCC rejection, this strategy was tested in combination with two irrigation schedules—irrigation to avoid water restriction at bloom (Ir) vs. no early irrigation—and two nitrogen inputs (0 vs. 100 kg N ha−1) over three growing seasons in southern Uruguay. Treatments were arranged in a split-split-plot randomized block design with cover crop schemes as main plots, water availability as subplots and nitrogen inputs as sub-subplots. Shoot growth rate, mid-day stem water potential (Ψstem), berry size and berry composition were monitored over the season, as well as final yield, cluster and pruning weights. UTCC significantly reduced vine vegetative growth, while no significant differences were detected between H and UTCC when irrigation took place early in the season. Even nitrogen input showed positive effects on grapevine vegetative growth in some cases, water availability at bloom was the key driver of vegetative growth. UTCC treatments increased grape soluble solids (TSS) in the last two out of three seasons and consistently increased anthocyanin concentration in grapes. Independent of vegetative growth, strong differences in bunch rot incidence were detected between H and UTCC treatments. Seasonal variations in water status and/or free amino nitrogen content of grapes may have a relevant impact on disease susceptibility at harvest.

Development and Validation of a New Methodology to Assess the Vineyard Water Status by On-the-Go Near Infrared Spectroscopy.

Assessing water status and optimizing irrigation is of utmost importance in most winegrowing countries, as the grapevine vegetative growth, yield, and grape quality can be impaired under certain water stress situations. Conventional plant-based methods for water status monitoring are either destructive or time and labor demanding, therefore unsuited to detect the spatial variation of moisten content within a vineyard plot. In this context, this work aims at the development and comprehensive validation of a novel, non-destructive methodology to assess the vineyard water status distribution using on-the-go, contactless, near infrared (NIR) spectroscopy. Likewise, plant water status prediction models were built and intensely validated using the stem water potential (ψs) as gold standard. Predictive models were developed making use of a vast number of measurements, acquired on 15 dates with diverse environmental conditions, at two different spatial scales, on both sides of vertical shoot positioned canopies, over two consecutive seasons. Different cross-validation strategies were also tested and compared. Predictive models built from east-acquired spectra yielded the best performance indicators in both seasons, with determination coefficient of prediction () ranging from 0.68 to 0.85, and sensitivity (expressed as prediction root mean square error) between 0.131 and 0.190 MPa, regardless the spatial scale. These predictive models were implemented to map the spatial variability of the vineyard water status at two different dates, and provided useful, practical information to help delineating specific irrigation schedules. The performance and the large amount of data that this on-the-go spectral solution provides, facilitates the exploitation of this non-destructive technology to monitor and map the vineyard water status variability with high spatial and temporal resolution, in the context of precision and sustainable viticulture.

Vinegar and Iron Chelate Spray Affected Vegetative Growth and Yield of Grape cv. Thompson Seedless

In soils with high pH, iron is inactivated and bounded to the leaf apoplast developing leaf chlorosis. The inactive iron can be reduced artificially by lowering leaf apoplastic pH with spraying weak acid solutions, providing the symplast absorption of activated iron. The objective of this study was to determine the effect of vinegar spray, as an acidifying substance and iron chelate (Fe-EDTA) on iron nutrition and vegetative growth of grape vines (cv. Thompson Seedless) grown in high pH soils. Four years old grape vines of cv. Thompson Seedless which were grown in high pH soil (pH=8) were selected. Experimental design was a Randomized Complete Block Design (RCBD) with four spray treatments: 1) vinegar (0.8%), 2) iron chelate (0.2%), 3) combination of vinegar and iron chelate (0.8%, 0.2% respectively) and 4) distilled water (control). Vinegar treated plants had higher chlorophyll, active iron (Fe2+) and yield. Vinegar is a by product of grapes that can be easily produced by growers with very little cost and its application has effectively improved plant vegetative growth, yield and mitigated iron deficiency of “Thompson Seedless” grapes. Vinegar is very cheap compared to chelated iron. The vinegar spray has the potential to increases yield without increasing the cost for the growers, ensuring both profitability and sustainability of the production system.

Effects of Seasonal Deficit Irrigation, Potassium Fertilization and Bunch Thinning on Growth, Yield and Quality of Flame Seedless Grapes

Impacts of deficit irrigation levels, potassium fertilization, and bunch thinning on grapevine vegetative growth, yieldand quality of Flame Seedless table grapes were investigated during 2012 and 2013 seasons. Vines were subjected toseasonal irrigation treatments from bud swell to dormancy including: Standard irrigation (100 % of cropevapotranspiration [ETc]), moderate deficit (80 % of ETc), and sever deficit (60 % of ETc). Effects of two levels ofpotassium fertilization (0 and 0.58 kg as K2O per vine per season) and bunch thinning (40 and 30 bunch per vine) werealso investigated. Results showed that vine petiole potassium concentration was significantly dependent upon appliedirrigation level and was highest in standard irrigated potassium fertilized vines. Shoot length, leaf area and pruning weightresponded negatively to irrigation deficit, while bunch thinning increased leaf area in both seasons and pruning weight inthe second season with no effect on shoot length, whereas potassium had no effects on vegetative growth. Vine yield,bunch weight and berry diameter increased significantly with increasing irrigation level and with potassium fertilization.Bunch thinning significantly decreased yield in first season only while increased bunch weight and berry diameter. Cropload (yield/pruning) significantly increased by potassium and decreased by thinning with no effect for irrigation. Wateruse efficiency (yield/irrigation) significantly increased by increasing irrigation level and by potassium fertilization whiledecreased in first season by thinning. Increasing deficit irrigation level resulted in increased berry juice total soluble solids(TSS) and declined titratable acidity (TA), decreased berry firmness, increased skin anthocyanin and total phenolics, andreduced skin color characteristics values of lightness (L*), chroma(C*) and hue angle(h°). Bunch thinning increased berryTSS in first season, did not affect TA and fruit firmness, and increased berry skin anthocyanin and total phenolics, whiledecreased skin L* in the first season, C* and h°. Potassium fertilization increased berry TSS, TA, anthocyanin, totalphenolics, did not affect firmness with no consistent effect on skin color characteristics.

Quantifying spatio-temporal variation of leaf chlorophyll and nitrogen contents in vineyards

Precision viticulture requires the characterisation of the spatio-temporal variability of the vineyard status to design the appropriate management for each area. The goal of this work was to characterise the spatio-temporal variability of leaf chlorophyll (Chl) and nitrogen (N) content and their relationship with the vegetative growth in a three ha commercial vineyard (Vitis vinifera L.) using a geostatistical approach. Leaf Chl and N contents were assessed by two fluorescence indices provided by a hand-held fluorescence sensor. Fluorescence measurements were taken along five dates, from veraison to harvest, on 72 sampling points delineated on a regular grid across the vineyard. Shoot pruning weight (SPW) was measured for each sampling point as indicator of the grapevine vegetative growth. Geostatistical analysis was applied to model the spatial variability of leaf Chl and N content and SPW. The spread showed an increase of the variability of leaf Chl and N content during the ripening period, reaching maximum values prior to harvest. The variograms illustrated a similarity of the spatial variability structure of leaf Chl at all timings, unlike N which showed changing spatial variability structures along the ripening period. The Kappa index evidenced a slight intra-season stability for both Chl and N and showed that N could not be used alone as an indicator to delineate vigour management areas. The existence of spatio-temporal variability of key vegetative components was proved and its knowledge is crucial to implement precision viticulture approach such as variable rate application of fertilizers or water as needed.

Root-zone management practices impact above and belowground growth in Cabernet Franc grapevines

Background and Aims The objective of this study was to assess the effect of root pruning (RP) and annual under-trellis cover crops (UTCC) on vegetative growth and physiological processes in Cabernet Franc (Vitis vinifera L.) grapevines grafted on 3309C rootstock. Methods and Results Five root-zone management treatments, namely under-trellis vegetation-free strip control (C), RP and three distinct annual UTCC [annual ryegrass (AR), buckwheat, (BW) and turnip (TP)] were evaluated and compared over three seasons in a vigorous vineyard in the Northeastern USA. Root pruning had the greatest impact in reducing grapevine size; AR reduced the duration of shoot growth 2 out of 3 years. Competition between grapevine and AR and BW fine roots resulted in a lower grapevine fine root production in shallow soil layers and in a decrease in fine root lifespan. Conclusions Root pruning was effective in reducing grapevine size for 3 years; RP effectiveness, however, may vary greatly depending on site conditions. Annual UTCC hold potential for reducing grapevine size in vigorous plantings in regions with ample precipitation. Appropriate choice of cover crop species, however, remains unclear. Significance of the Study This work demonstrates that root-zone management practices impact grapevine vegetative growth and induce changes in root morphological traits.

Integrated analysis of climate, soil, topography and vegetative growth in Iberian viticultural regions.

The Iberian viticultural regions are convened according to the Denomination of Origin (DO) and present different climates, soils, topography and management practices. All these elements influence the vegetative growth of different varieties throughout the peninsula, and are tied to grape quality and wine type. In the current study, an integrated analysis of climate, soil, topography and vegetative growth was performed for the Iberian DO regions, using state-of-the-art datasets. For climatic assessment, a categorized index, accounting for phenological/thermal development, water availability and grape ripening conditions was computed. Soil textural classes were established to distinguish soil types. Elevation and aspect (orientation) were also taken into account, as the leading topographic elements. A spectral vegetation index was used to assess grapevine vegetative growth and an integrated analysis of all variables was performed. The results showed that the integrated climate-soil-topography influence on vine performance is evident. Most Iberian vineyards are grown in temperate dry climates with loamy soils, presenting low vegetative growth. Vineyards in temperate humid conditions tend to show higher vegetative growth. Conversely, in cooler/warmer climates, lower vigour vineyards prevail and other factors, such as soil type and precipitation acquire more important roles in driving vigour. Vines in prevailing loamy soils are grown over a wide climatic diversity, suggesting that precipitation is the primary factor influencing vigour. The present assessment of terroir characteristics allows direct comparison among wine regions and may have great value to viticulturists, particularly under a changing climate.

Influence of retained node number on Sauvignon Blanc grapevine vegetative growth and yield

Background and Aims The potential yield of grapevines is often inexpensively manipulated by altering the number of nodes retained per vine after pruning. In the context of Sauvignon Blanc in Marlborough New Zealand the influence of node number on grapevine performance is not well documented. To address this void a multi-year field study examined the effect of node number on Sauvignon Blanc grapevine growth and yield. Methods and Results A replicated field experiment was established by winter pruning the same grapevines to 24–72 nodes per vine (two, three, four, five or six 12-node canes per vine) over a 4-year period. Increasing the number of nodes resulted in a linear increase in vine yield in 2007. In subsequent years, the yield response decreased and from 2009 onwards, increasing the number of nodes beyond 36 per vine did not increase yield. Fewer nodes per vine were associated with greater vegetative growth and cane vigour. Pre-flowering shoot length, leaf number and shoot diameter along with end of season mean cane mass were greatest in vines with fewer nodes. Conclusions The dynamic interseasonal yield responses were caused by a combination of changes in bunches per vine and bunch mass, although the contribution of each yield component altered during the course of the experiment. Changes in cane vigour and bunches per shoot (fruitfulness) suggest that they are part of the mechanisms by which vines moderate yield over time in response to altered node number. Significance of the Study Increasing or reducing node number per vine does not result in sustained yield increases or reductions respectively. Grapegrowers should expect the level of yield compensation to change after the first year of a change in node number. Therefore, adjustment of nodes per vine and the selection of appropriate cane vigour at pruning should be considered carefully when setting the annual yield potential of Sauvignon Blanc grapevines.

Complete vineyard floor cover crops favorably limit grapevine vegetative growth

Complete vineyard floor cover crops were evaluated in a long-term study for their ability to regulate excessive vegetative growth of the grapevine (Vitis vinifera L.) variety ‘Cabernet Sauvignon’. Treatments were: tall fescue (Festuca arundinacea Shreb.) ‘KY-31′ and ‘Elite II’, hard fescue (Festuca ovina L.) ‘Aurora Gold’, perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), and an under-trellis herbicide strip combined with KY-31 fescue interrows. Compared to herbicide-treated soil strip, Elite II fescue reduced vine pruning weights (kg/vine) 28%, individual cane weight (g) 20%, and canopy leaf layer number 25%. KY-31 fescue produced the greatest biomass and stand density, while perennial ryegrass produced the least biomass and Aurora Gold hard fescue produced the lowest stand density. Elite II fescue produced less biomass but equivalent stand density compared to KY-31 fescue. Treatments minimally impacted vine water potential (Ψmd, Ψstem), indicating that the grasses were not overly competitive with grapevines for soil moisture. All grass treatments tended to depress grapevine nitrogen levels relative to the under-trellis herbicide strip treatment, but no treatment resulted in vine nitrogen levels below the acceptable sufficiency range. Because of its establishment and growth characteristics, desired suppression of vine vegetative growth, and its low impact on crop yield, we considered Elite II fescue the optimal cover crop evaluated.

Asymmetric warming effect on the yield and source:sink ratio of field-grown grapevine

Using large-scale open-top chambers to approximate the thermal regimes of the Barossa Valley in the next decades, we measured yield and vegetative growth of grapevines in three factorial field experiments combining two thermal regimes (elevated temperature vs. control) with: two water regimes (experiment 1), two source:sink ratios generated by manipulation of fruit load (experiment 2) and four varieties (experiment 3). Water regime, source:sink ratio and varieties are sources of variation typically embedded in climate change studies using time series.Yield of controls ranged from 1.2 to 10.5kgvine−1. Warming had asymmetric effects on fruit yield and fruit/pruning weight ratios: yield response to elevated temperature varied from 46% reduction to 177% increase in relation to controls, and the response of fruit/pruning weight ratio varied from 56% reduction to 145% increase. Yield response to temperature was primarily explained by the response of bunch number (r2=0.92, P<0.0001). The effect of elevated temperature on fruit/pruning weight ratio was closely related to the response of fruit yield (r2=0.79, P<0.0001) and unrelated to the response of pruning weight (P=0.18). Elevated temperature reduced concentration of starch in trunks but not in roots.We conclude that the asymmetric responses of yield and fruit/pruning weight ratios resulted from seasonal influences on warming effects, whereby the largest responses of these traits were mediated by the promotion of bunch formation following relatively low temperatures in the preceding season. This highlights the need to assess warming effects in the light of both the background temperature and the distribution of thermally contrasting seasons in particular locations. Lower source:sink ratio and reduced starch concentration in trunks are two important elements of the carbon balance of the vine with long-term physiological and viticultural implications.

Cover cropping in &lt;em&gt;Vitis vinifera&lt;/em&gt; L. cv. Manto Negro vineyards under Mediterranean conditions: effects on plant vigour, yield and grape quality

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aims&lt;/strong&gt;: In temperate climates, cover crops are mainly used to reduce excess soil water and nutrient availability to grapevines, which otherwise could decrease grape quality. In Mediterranean climates, where water is a limiting factor, the use of cover crops is not as straightforward. However, in this scenario, summer senescent and self-seeding herbaceous cover crops could also help to decrease soil erosion as well as to reduce excessive early vegetative vigour, which could restrict grape water availability at later phenological stages. The aim of this experiment was to study the effects of particular cover crops in Mediterranean vineyards on grapevine vegetative growth, gas exchange, yield and grape quality.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: The experiment was carried out over three consecutive years in an organic vineyard (cv. Manto Negro) in central Majorca, Spain. Three treatments (three cover cropping rows per treatment) were established: perennial grass and legume mixture (PM), no tillage, i.e., with permanent resident vegetation (NT), and traditional tillage or ploughed soil (TT). The grapevines were rain fed until veraison, and then drip irrigation was applied (30% potential evapotranspiration; ETP) until harvest. Plant water status was established according to a defined value of maximum daily leaf stomatal conductance (g&lt;sub&gt;s&lt;/sub&gt;). Cover crops reduced total leaf area (LA), g&lt;sub&gt;s&lt;/sub&gt; and grapevine vigour at early growth stages. g&lt;sub&gt;s&lt;/sub&gt; and net photosynthesis (A&lt;sub&gt;N&lt;/sub&gt;) were higher in cover crop treatments during the veraison and ripening stages, likely because of the reductions in LA. Intrinsic water use efficiency increased from flowering to veraison-maturity in all treatments. Yield was lower in the cover crop treatments (PM and NT) compared to TT for all years, but these differences were only significant in 2007. However, grape quality parameters slightly improved in the PM treatment.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;: The use of cover crops decreased LA, helping to avoid dramatic reductions of stomatal conductance in mid-summer, but decreased yield and only slightly increased grape quality.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of the study&lt;/strong&gt;: This study showed that the use of specific cover crops in vineyards under Mediterranean climates helps to reduce vegetative vigour. Nevertheless, yield reduction and slight quality improvement suggest that cover crops should be adjusted in order to reduce competition for water and thus prevent these negative effects of water scarcity.&lt;/p&gt;

Powdery mildew development is positively influenced by grapevine vegetative growth induced by different soil management strategies

In various crop species, high levels of powdery mildew infection and severity have been associated with high vegetative vigour. In grapevine this relationship has also been observed by vine growers, though it has not been quantified. This study was undertaken to investigate the relationship between the development of powdery mildew on leaves and berries and canopy growth, and thus to quantify the relationship between the pathogen and its host. Over a two-year period (2005 and 2006), an experiment was carried out in a vineyard (cv. Aranel) near Montpellier, southern France. Several levels of canopy growth were generated by implementing four soil management strategies: i) perennial cover crop in the inter-row, ii) annual cover crop in the inter-row, iii) chemical weed control over the entire soil surface, iv) chemical weed control all over the soil surface and drip irrigation and fertilization in the row. Powdery mildew was artificially inoculated on experimental sub-plots with Erysiphe necator [Schw.] Burr. conidia. The most vigorous vines developed a larger number of diseased leaves and a higher percentage of mildewed berries compared to low-vigour vines. The major explanatory variable highlighted in these experiments was the shoot leaf number, mainly early in the season. A higher leaf population generated a larger number of powdery mildew colonies close to grapes and consequently a higher probability of berry infection. Our experimental results provide evidence of a positive relationship between powdery mildew development and grapevine vegetative development. These results provide an opportunity to develop new IPM strategies in vineyards.