• Irrigation is illegal in many wine growing regions throughout Europe in part due to the traditional view that water deficits promote winegrape quality.  Experimentally, water deficits consistently promote one quality parameter, higher concentrations of anthocyanins in red winegrapes and their wines.  However, controversy remains as to whether there is any direct effect on berry metabolism other than inhibition of growth.  We are characterizing the effects of the timing of water deficits on: (1) berry maturation, (2) the accumulation of anthocyanins, proanthocyanidins and flavonols, and (3) the expression of structural and regulatory genes of the flavonoid pathway in berry skin. CLICK HERE FOR MORE!

• We are using various microscopy techniques to describe changes in berry anatomy throughout ripening into extended hang times. With these techniques we are able to generate 3-dimensional images of flesh cells in the berry. Click the fluoroscein diacetate (FDA) stained berry below and link to a 3-dimensional movie taken from a pre-verasion berry section that was exposed to FDA, which enters viable cells and fluoresces when exposed to the correct activating light. The movie shows viable cells due to the fluorescence arising from the thin layer of cytoplasm in each cell.

• We use the cell pressure probe to measure turgor, hydraulic conductivity, and cell wall elasticity in situ to better understand the water relations during berry development. Currently we are working to automate the probe using machine vision.
• Watch a Movie of the Automated Machine Vision tracking the meniscus of the pressure Probe

• During the development of (Vitis vinifera L.), water flow changes from being predominantly xylemic to being predominantly phloemic.  The accepted hypothesis to explain this change is that the tracheary elements of the peripheral xylem break as a result of berry growth, rendering the xylem nonfunctional. However, recent work in our laboratory suggests that the xylem remains functional throughout berry development. More!

• 2006 Thomas, T. R., Shackel, K. A., Matthews, M. A.. Direct in-situ measurement of cell turgor in grape (Vitis vinifera L.) berries during development and in response to plant water deficits. Plant, Cell and Environment 29:993-1001.

• 2005 Bondada, B. R., M. A. Matthews, and K. A. Shackel.  Functional xylem in the post-veraison grape berry. Journal of Experimental Botany 56:2949-2957.

• 2005 Matthews, M. A. and K.A. Shackel.  Growth and Water Transport in Fleshy Fruit. pp 181-197. In, Vascular Transport in Plants, N.M. Holbrook and M.A. Zwieniecki (Eds.)

• The exact mechanisms of Xylella fastidiosa (Xf) pathogenicity remain unknown. Recently genomic sequencing revealed that Xf harbors known bacterial RTX-toxins, proteins known to disrupt host cell functioning, reviving old speculation that phytotoxins may be involved Xf pathogenicity. These proteins along with other virulence-associated proteins, including host-derived signals, have the potential to elicit a variety of plant defense responses leading to programmed cell death (PCD), lesion formation, and eventually premature leaf senescence and vine death. The objective of this study is to identify Xf and host-derived elicitors and characterize the plant’s signaling responses during Pierce’s Disease. CLICK FOR MORE

• Characterizing Xylella fastidiosa populations via quantitative PCR reveals an interesting relationship between bacterial load and Pierce's Disease leaf scorch symptoms. Click here to read more from a PDF of Greg Gambetta's poster presentation at this year's CDFA Pierce's Disease Research Symposium.

• Many plants harbor the bacteria with little or no visible symptoms.  In order to better comprehend how the xylem network might influence bacterial movement and contribute to pathogenicity we are investigating xylem structure, and its relation to the movement of Xf, by comparing different hosts that are able to support systemic and non-systemic Xf infection. MORE!

• 2006 Chatelet, D.S., M. A. Matthews, and T.L. Rost. Xylem Structure and Connectivity in Grapevine (Vitis vinifera) Shoots Provides a Passive Mechanism for the Spread of Bacteria in Grape Plants. Annals of Botany 98(3):483-494.

• 2006 Thorne, E., B.M. Young, G. M. Young, J.F. Stevenson, J.M. Labavitch, M. A. Matthews, and T.L. Rost. The Structure of xylem vessels in grapevine and a possible passive mechanism for the systemic spread of bacterial disease. American Journal of Botany 93(4):497-504.

• 2006 Thorne, E. T., J. F. Stevenson, T. L. Rost, J. M. Labavitch, and M. A. Matthews. Pierce’s Disease symptoms: Comparison with symptoms of water deficit and the impact of water deficits. American Journal of Enology and Viticulture 57(1):1-11.

• 2005 Stevenson, J. F., M. A. Matthews, and T. L. Rost. The developmental anatomy of “Green Islands” and “Matchsticks” as symptoms of Pierce’s Disease of grapevines. Plant Disease 89:543-548.

• That small berries are superior to big berries, and that high yield translates into low quality, are two prevalently held dogmas within the wine industry.  Data suggest that it is the journey rather than the destination that determines wine grape composition and wine sensory attributes. Click here for more…

• Berry shrivel (BS) and bunch stem necrosis (BSN) are two disorders that afflict vines in the Napa/Sonoma viticultural areas, and symptomatic fruit is usually dropped in the vineyard prior to harvest.  Both disorders involve the visible shriveling of the berries during ripening. Click here for more info...

• Is there an optimal point during the ripening of a grape that will produce the best tasing wine? If there is a time point, what chemical compounds inside the grape would indicate this optimal harvest time? A three year study, using senitive analyical insturments, to monitor Cabernet Sauvginon grapes from a vineyard in Paso Robles will try to determine what chemical changes happen and when. We hope to begin to build an optimal ripening profile for Cabernet Sauvginon using SPEME-CG/MS and Harberson & Adams Assay.

• 2005 Chapman, D. M., Gaspar, R., Ebeler, S. E., Guinard, J.-X., and Matthews, M. A..  Sensory attributes of Cabernet Sauvignon wines made from vines with different water status. Australian Journal of Grape and Wine Research 11:339-347.

• 2004 Chapman, D. M., M. A. Matthews, and J.-X. Guinard. Sensory attributers of Cabernet Sauvignon wines made from vines with different crop yields. American Journal of Enology and Viticulture 55:325-334.

• 2004 Roby, G., J. F. Harbertson, D. O. Adams, and M. A. Matthews. Berry size and vine water deficits as factors in winegrape composition: Anthocyanins and tannins. Australian Journal of Grape and Wine Research 10:100-107.

• 2004 Roby, G. and M. A. Matthews. Relative proportions of seed, skin and flesh, in ripe berries from Cabernet Sauvignon grapevines grown in a vineyard either well irrigated or under water deficit. Australian Journal of Grape and Wine Research 10:74-82.

The lab out in the field harvesting BSN and berry shrivel grapes for wine production and subsequent sensory analysis. From left to right: Ken Shackel, Brendan "my arms hurt" Choat, Derek Cronk (Solinas Farming Company) and Mark Matthews, Alfredo Koch, and David Chatelet.