Markus Keller

Washington State University | WSU · Department of Horticulture

Anthocyanin composition is responsible for the red color of grape berries and wines, and contributes to their organoleptic quality. However, anthocyanin biosynthesis is under genetic, developmental and environmental regulation, making its targeted fine-tuning challenging. We constructed a mechanistic model to simulate the dynamics of anthocyanin co...

Anthocyanin composition is responsible for the red color of grape berries and wines, and contributes to their organoleptic quality. However, anthocyanin biosynthesis is under genetic, developmental and environmental regulation, making its targeted fine-tuning challenging. We constructed a mechanistic model to simulate the dynamics of anthocyanin co...

Recurring heat and drought episodes present challenges to the sustainability of grape production worldwide. We investigated the impacts of heat and drought stress on transcriptomic and metabolic responses of berries from two wine grape varieties. Cabernet Sauvignon and Riesling grapevines were subjected to one of four treatments during early fruit...

In ripening grape (Vitis sp.) berries, the combination of rapid sugar import, apoplastic phloem unloading, and water discharge via the xylem creates a potential risk for apoplastic sugar to be lost from the berries. We investigated the likelihood of such sugar loss and a possible sugar retrieval mechanism in the pedicels of different Vitis genotype...

The skin protects a fruit from environmental stresses and supports the fruit’s structure. Failure of the skin leads to fruit splitting and may compromise commercial production for fruit growers. The mechanical properties of the cuticle and skin cell walls might influence the splitting susceptibility of fleshy fruits. Thin shell theory and fracture...

Background and Aims The grape ripening disorder called berry shrivel is characterised by cessation of sugar accumulation, low pH, impaired anthocyanin biosynthesis in dark‐skinned cultivars and water loss. We tested whether damage to the bunch peduncle vasculature can induce berry shrivel and whether cell death in the rachis precedes cell death in...

Knowledge about heat acclimation in perennial plants is limited. Our hypotheses were (i) that high temperature during budswell before budbreak elicits acclimation in grapevines that is mediated by greater water transport capacity, and (ii) that water deficit modulates acclimation to high temperature. We compared field grown Malbec grapevines heated...

Vitis vinifera is a species of temperate origin that reactivates the dormant secondary phloem from the previous year at the resumption of growth in spring. Following harsh winters, grapevines may display a set of symptoms including delayed and heterogeneous budbreak, dieback with shoot renewal from the trunk base or sudden death of the plant. Altho...

The complex environment within a crop canopy leads to a high variability of the air temperature within the canopy, and, therefore, air temperature measured at a weather station (WS) does not represent the internal energy within a crop. The objectives of this study were to quantify the difference between the air temperature measured at a standard WS...

Dormancy is an evolutionary strategy to overcome adverse conditions during winter through the interruption of growth and metabolism. Winter dormancy is divided into two phases: endodormancy when bud growth is inhibited internally, and ecodormancy when adverse environmental conditions impede growth. The study of winter dormancy is limited because th...

Vitis vinifera is a species of temperate origin that reactivates the dormant secondary phloem from the previous year at the resumption of growth in spring. Following harsh winters, grapevines may display a set of symptoms including delayed and heterogeneous budbreak, dieback with shoot renewal from the trunk base or sudden death of the plant. Altho...

Main conclusion Applying principles of shell theory, we found that grape berries rapidly change their behavior from thick-walled spheres to pressurized thin-walled spheres and become susceptible to splitting during berry softening. Abstract Knowledge of the rheological properties of the skin of berry fruits is needed to make decisions concerning b...

Main conclusion: Foliar sugar accumulation in grapevines with leafroll disease was correlated with lower photosynthesis, likely due to feedback inhibition. However, cold acclimation of dormant tissues remained unaffected by the virus status. Grapevine leafroll-associated viruses (GLRaV) contribute to losses in fruit yield and quality worldwide. Vi...

Background The reduced growth of plants during the winter causes a lack in the perceptibility of the phenological events making challenging the study of dormancy. For deciduous crops, dormancy is generally determined by evaluating budbreak of single-node cuttings that are exposed to conditions suitable for growth. However, the absence of a statisti...

The growth and development of grapevines Vitis vinifera L. are highly dependent on the weather dynamics of a region. The goal of this study was to use long-Term historical weather data to obtain and develop several bioclimatic indices that are of viticultural importance. In this study, several bioclimatic indices were computed using 30 yr (1983-201...

Vitis vinifera is mainly cultivated in temperate areas, where seasons are well defined and winter conditions might be severe. To survive under these conditions during the dormant season, grapevines sense environmental parameters to trigger different protective mechanisms that leads to cold hardiness (CH). Crop yield and sustainability will be deter...

Der Ertrag eines Weinbergs oder einer Anbauregion ist jahrgangsbedingten Schwankungen unterworfen. Die vorliegenden statistischen Untersuchungen basierend auf einem 22-jährigen Datensatz der jährlichen Erträge der Rebsorten Müller-Thurgau und Riesling in der Weinbauregion Luxemburgs belegten, dass die meteorologischen Bedingungen in spezifischen Ph...

The juice grape (Vitis labruscana) cultivar Sunbelt has been reported to ripen more uniformly than the cultivar Concord in warm climates; thus, ‘Sunbelt’ might be useful as either a blending partner with or replacement for ‘Concord’ as global climate change intensifies. We conducted a 4-year field trial to evaluate ‘Sunbelt’ alongside ‘Concord’ in...

Low temperature is a limiting factor that affects vineyard distribution globally. The level of cold hardiness acquired during the dormant season by Vitis sp. is crucial for winter survival. Most research published on this topic has been generated beyond 40° N latitude, where daily mean temperatures may attain injurious levels during the dormant sea...

Fruit ripening can be delayed or hastened by chemical means to time harvest at desired dates; however, it is not clear if the ripening window can be extended merely by delaying harvest in nonclimacteric fruits such as grape to optimize fruit quality. In this study, we investigated the consequences of extending ripening known as “hang time” in vitic...

Modifications of plant hydraulics and shoot resistances (Rshoot) induced by water withholding followed by rewatering, and their relationships with plant water status, leaf gas exchange and water use efficiency at the leaf level, were investigated in pot-grown and field-grown, own-rooted Syrah grapevines in an arid climate. Water stress induced anis...

At the onset of ripening, some fleshy fruits shift the dominant water import pathway from the xylem to the phloem, but the cause for the decline in xylem inflow remains obscure. This study found that xylem-mobile dye movement into grape berries decreased despite transient increases in berry growth and transpiration during early ripening, whereas ou...

p style="text-align: justify;"> Background and Aims: Grape yields show distinct interannual fluctuations caused by environmental conditions. Statistical investigations based on a 22-year data set (1993-2015) of annual yields of two grape cultivars grown in Luxembourg aimed at (i) investigating the impact of meteorological conditions during specifi...

Cold injury is a major cause of economic loss in winegrapes (Vitis vinifera L.) grown at high latitudes. The objective of this study was to investigate the relationship between dormancy and cold hardiness transitions in two cultivars with differing freeze tolerance (Chardonnay and Cabernet Sauvignon). Cold hardiness was measured by differential the...

Weather conditions have a significant impact on crops, and temperature is one of the main factors that controls plant development. Thermal time models based on temperature have been applied to predict the development of many species. To implement these models, determination of an appropriate base temperature (T-b) is required to characterize the di...

Berry samples were collected over four growing seasons from field-grown Cabernet Sauvignon grapevines in the Columbia Valley of southeastern Washington. Shoots were tagged prior to veraison and berries were sampled weekly from the same clusters. Symptoms of berry shrivel (BS) and bunch-stem necrosis (BSN) were monitored through harvest and berry sa...

A deficit irrigation trial was conducted with field-grown Cabernet Sauvignon grapevines in the Columbia Valley of southeastern Washington. Four irrigation regimes were applied in four replicated blocks to replace various fractions of crop evapotranspiration (ETc) between fruit set and harvest. These treatments were designated ET100 (100% ETc), ET70...

The effects of abscisic acid (ABA) form, concentration, and application timing on bud cold hardiness, phenology, and fruiting performance of Merlot grapevines (Vitis vinifera) were evaluated in a three-year field trial with site locations in British Columbia and Ontario, Canada, and in Washington and Idaho, United States. Solutions containing natur...

On-farm research offers many opportunities to understand the effectiveness of various management practices and products. However, how these trials are designed can alter the observed results. This guide summarizes the concepts of experimental design and how those concepts are important in conducting field trials and understanding their results. It...

Photosynthesis is the most important way of obtaining energy for all plants including grapevines. The electron released from the reaction center chlorophyll is transferred to an acceptor molecule in a process termed photochemical quenching because it “quenches” the excitation energy of the chlorophyll. Photorespiration reduces the efficiency of pho...

Developmental changes and factors determining grape berry transpiration were investigated in three genetically diverse Vitis cultivars. Transpiration rates were measured on whole clusters, using a custom-designed cluster chamber, and on individual berries by weighing detached berries over time. Results obtained using the two methods were in good ag...

Four regulated deficit irrigation (RDI) regimes were applied to Cabernet Sauvignon grapes, which were analyzed for phenolics and also made into wine over three consecutive growing seasons. Relative to an industry standard regime (IS), yield was reduced over the three years by 37% in a full-deficit (FD) regime and by 18% in an early deficit (ED) reg...

Thermal time models have been used to predict the development of many different species, including grapevine (Vitis vinifera L.). These models normally assume that there is a linear relationship between temperature and plant development. The goal of this study was to estimate the base temperature and duration in terms of thermal time for predicting...

The rate of shoot growth (vigour) in grapevines tends to decrease as the number of shoots per plant increases. Because the underlying causes of this relationship remain unclear, they were studied by variable pruning of field-grown, deficit-irrigated Merlot grapevines (Vitis vinifera L.). Shoot number ranged from 11 to 124 per vine and was inversely...

The Science of Grapevines: Anatomy and Physiology is an introduction to the physical structure of the grapevine, its various organs, their functions and their interactions with the environment. Beginning with a brief overview of the botanical classification (including an introduction to the concepts of species, cultivars, clones, and rootstocks), p...

This four-year study tested whether the physiological demand of fruit ripening may interfere with grapevine cold acclimation in autumn or with midwinter hardiness. Three harvest time treatments were established in a mature vineyard of own-rooted Cabernet Sauvignon vines: clusters were removed after fruit set, at veraison, or after the first fall fr...

We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink-driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought-induced berry shrinkage. Rew...

Weather conditions have a significant impact on crop growth and development. The main controlling factor is temperature which affects plant development and many other plant processes. Phenological models such as thermal time or Growing Degree Day model have been widely applied to predict the development of many species. These concepts can also be a...

Irrigation practices such as regulated deficit irrigation (RDI) and winemaking practices such as extended maceration have been experimentally evaluated from a chemical perspective but their impacts on sensory composition and interactive effects merit scientific attention. This study evaluated the sensory impact of extended maceration applied to Cab...

Cold injury is a key environmental challenge in many grape-producing regions, especially those at high latitudes. Although grapevines acclimate to cold temperatures in fall and deacclimate when warm temperatures return in spring, cold hardiness varies with species, cultivar, phenology, ambient weather, photoperiod, and plant organ, which hampers im...

Phloem unloading is thought to switch from a symplastic route to an apoplastic route at the beginning of ripening in grape berries and some other fleshy fruits. However, it is unclear whether different solutes accumulate in both the mesocarp vacuoles and the apoplast. We modified a method developed for tomato fruit to extract apoplastic sap from gr...

The impact of extended maceration (EM) was studied in Cabernet Sauvignon grapes sourced from a vineyard subjected to four regulated deficit irrigation (RDI) treatments: (I) 100% replenishment of crop evapotranspiration (100% ETc), (II) 70% ETc, (III) 25% ETc until véraison, followed by 100% ETc until harvest, and IV) 25% ETc. Each vineyard replicat...

A rootstock field trial was conducted in the Yakima Valley, southeastern Washington, with three Vitis vinifera cultivars (Merlot, Syrah, Chardonnay). Vines were grown on their own roots or field-grafted to the rootstocks 5C, 99R, 140Ru, 1103P, 3309C, and an unnamed rootstock from Cornell University (here termed 101CU) that is a likely sibling or se...

The accurate prediction of winter injury caused by low-temperature events is a key component of the effective cultivation of woody and herbaceous perennial plants. A common method employed to visualize geographic patterns in the severity of low-temperature events is to map a climatological variable that closely correlates with plant survival. The U...

Berry shrivel, a physiological disorder, adversely affects ripening of grape (Vitis vinifera L.) berries; however, its causes are unknown. We adopted a holistic approach to elucidate symptomatology, morphoanatomy, and osmotic behavior of grape berry shrivel. Berries from healthy and afflicted vines were analyzed compositionally and with various tec...

Step-by-step guide on how to determine if your grapevines have been damaged by cold temperatures, as well as ways to avoid the problem.

Whole-canopy net CO2 exchange (NCEC) was measured near key stages of fruit development in grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) that were managed under three approaches to regulated deficit irrigation (RDI): (1) standard practice (RDIS), or weekly replacement of 60–70% of estimated evapotranspiration for well watered grapevines; (2)...

This study compared own-rooted vines and different scion/rootstock combinations in arid eastern Washington, where vineyards are primarily deficit-irrigated and own-rooted. The performance of Chardonnay, Merlot, and Syrah on five rootstocks (5C, 140Ru, 1103P, 3309C, and 101CU) or on their own roots was evaluated with 10 field replicates over three v...

Grapevine (Vitis spp.) cold hardiness varies dynamically throughout the dormant season, primarily in response to changes in temperature. The development and possible uses of a discrete-dynamic model of bud cold hardiness for three Vitis genotypes are described. Iterative methods were used to optimize and evaluate model parameters by minimizing the...

The basic unit of biological classification is the species. Although each individual of a sexual population is genetically unique, each species is a closed gene pool, an assemblage of organisms that does not normally exchange genes with other species. This chapter provides a brief overview of the botanical classification of grapevines, starting wit...

A stress limits either the availability of one or several resources to the plant or the plant's ability to put these resources to use. The optimum resource allocation hypothesis holds that plants respond to insufficient resource availability by investing biomass in those organs and processes that enhance the acquisition of the resource that most st...

The amount of fruit production in a given year and over the lifetime of grapevines determines both their reproductive success as a species and their agronomic trait of yield potential. Viticultural yields are determined by the amount of carbohydrate (sugar) partitioned to the fruit rather than to other organs. Yield formation is often referred to a...

Water serves as a solvent for ions and organic molecules in the interior of the vine's cells. Water can diffuse freely, albeit slowly, across the phospholipid bilayer of cell membranes, which are approximately 5–10 nm thick, and diffusion accelerates with rising temperature. Although the main force driving water movement through plants is water pre...

Grapevines employ a division of labor between different tissues and organs that are coupled to their structural framework and rely on an efficient transport system connecting the various parts. All leaves are initially sinks because they need to build up their photosynthetic machinery before they can start producing and exporting their own sugar. T...

Phenology is mainly concerned with the timing of specific stages of growth and development in the annual cycle. Such knowledge can be used for site and cultivar selection, vineyard design, planning of labor and equipment requirements, and timing of cultural practices as part of vineyard management. The annual growth cycle of mature, fruiting grapev...

Rachises of grape (Vitis vinifera L.) clusters that appeared healthy or displayed symptoms of the ripening disorders berry shrivel (BS) or bunch-stem necrosis (BSN) were treated with the cellular viability stain fluorescein diacetate and examined by confocal microscopy. Clusters with BS and BSN symptoms experienced a decrease of cell viability thro...

Background and Aims: Climate variation contributes to fluctuations in reproductive output, and spring temperature is thought to influence flower production in grapevines. For 3 years, we studied the influence of temperature from before budswell through to the appearance of individual flowers on reproductive development in field-grown Cabernet Sauvi...

Wine grape cluster compactness varies among varieties from loose to tight clusters, and can have implications in disease management. Grape varieties with loose cluster architecture may allow for additional air circulation throughout the cluster, reducing disease incidence. European studies have indicated that cutting the apical portion of infloresc...

Written by a recognized expert, and based on his experience in teaching the subject to students with a variety of educational backgrounds, The Science of Grapevines: Anatomy and Physiology is the only book to comprehensively explore the physiology of the grapevine as it occurs around the world. While other books have focused on the vines of specifi...

Grapevine reproductive development extends over two seasons, and the genotypic expression of yield potential and fruit composition is subject to environmental impacts, which include viticultural manipulations, throughout this period. This paper reviews current knowledge on yield formation and fruit composition and attempts to identify challenges, o...

Winegrape samples were collected from 2001 to 2003 in vineyards located in the Pacific Northwest. Riesling and Chardonnay had lower concentrations of biotin (often <1 μg/L) than did red cultivars. The concentration of pantothenic acid (mean 513 ± 181 mg/L) was lowest in Riesling but highest in Chardonnay. Most samples contained low amounts of yeast...

Although the inland Pacific Northwest has a warm climate during the growing season, grapes grown in this region may be exposed to colder than optimal temperatures at several times during the year. In addition to damage from spring and fall frosts, intermittent winters with little to no snow cover and subzero temperatures can cause vine dieback and...

Regulated deficit irrigation (RDI) and crop-load adjustment are regarded as important viticultural practices for premium-quality wine production, although little is known about their interactive effects. Crop loads were altered on field-grown, own-rooted Cabernet Sauvignon grapevines exposed to RDI varying in severity and timing in the arid Columbi...

This study investigated the response to nitrogen (0 or 100 kg N/ha) of field-grown Müller-Thurgau grapevines grafted on six rootstocks (Kober 5BB, Teleki 5C, Teleki 8B, Selection Oppenheim 4, Couderc 3309, Ruggeri 140). Half the nitrogen was applied four weeks pre-flowering and half at the end of flowering. Glutamine accounted for over 85% of xylem...

Ripening berries of Vitis vinifera (L) cv. Shiraz can show pre-harvest weight loss at sub-optimal sugar content (shrinkage). This later-age decline in berry weight implies that water loss from mature berries has begun to exceed water inflow from the parent grapevine. Such decrease in net inflow has been attributed to a cessation of xylem flow subse...

Nitrogen fertiliser was applied at two rates (0 or 100 kg N/ha) to field-grown Müller-Thurgau grapevines grafted onto six rootstocks (Kober 5BB, Teleki 5C, Teleki 8B, Selection Oppenheim 4, Couderc 3309, Ruggeri 140). Half the nitrogen was applied four weeks pre-flowering and half at the end of flowering. Nitrogen supply reduced symptoms of inflore...

Regulated deficit irrigation (RDI) and crop-load adjustment are regarded as important viticultural practices for premium-quality wine production, although little is known about their interactive effects. Crop loads were altered on field-grown, own-rooted Cabernet Sauvignon grapevines exposed to RDI varying in severity and timing in the arid Columbi...

Sensory evaluation was used to determine the aroma threshold of Harmonia axyridis (multicolored Asian lady beetle [MALB]) in Concord grape juice. Prior to Concord grape juice preparation, MALB was added to the Concord grapes at concentrations of 0 and 8.4 MALB/kg fresh grapes. To determine the odor threshold, the three alternative forced‐choice met...

A field experiment was conducted to determine effects of pruning time and bud number on vine recovery and performance following cold injury to trunk tissues. Own-rooted Merlot grapevines planted in 1999 and trained to a bilateral cordon with vertical shoot-positioning were pruned in 2003 and 2004 as follows: prebudbreak spur pruning, postbudbreak s...

The viticultural effects of sward competition with vines for water and nutrients, indirectly resulting from reduced herbicide use under a sustainable production system, are well established in cooler, more humid areas but are less well understood in warm and dry areas. Three groundcover treatments-standard industry practice of herbicide-treated und...

A system for differential thermal analysis (DTA) was constructed to assess cold hardiness of grapevine buds and cane tissues. This updated system incorporated a sample chamber of our own design with a commercially available programmable freezer and data acquisition system (DAS). Thermoelectric modules (TEM) were used to sense exotherms that are pro...

Trials were established in four Semillon hot-climate vineyards to determine the importance of the postharvest period for vines grown under different cropping levels and management practices. Two sites were chosen in high-yielding, furrow-irrigated vineyards in the Riverina region, and two in lower-yielding, drip-irrigated vineyards in the neighbori...

Shiraz berries commonly lose weight during the later part of ripening and loss of vascular flows into the berry may be a contributing factor. Changes in flow through the vascular streams were assessed by monitoring the accumulation of potassium and calcium in berries at the preveraison, postveraison, and shrinkage stages of development. Potassium,...