TEXAS & NUT PRODUCTION Pierce’s Disease- Tolerant

Jim Kamas, Larry Stein & Monte Nesbitt Extension Fruit Specialists, AgriLife Extension

Introduction vascular constriction inhibits the movement of The single greatest threat to the long-term sur- water through the grapevine and often results vivability of susceptible is in first visible symptoms noted during periods Pierce’s disease (PD). PD is caused by a - of heat or drought stress. Symptoms of the dis- limited bacterium that clogs the vascular tissue ease include irregular leaf scorch, abscision of of susceptible grape cultivars. The causal or- the leaf blade with retained petioles (leaf ganism is a gram-positive, rod-shaped bacte- stems) uneven periderm formation and finally rium named that is indige- cordon die-back and death. nous to the Gulf Coast region of the . Although different races of this organ- The risk of Pierce's disease varies in different ism cause similar diseases in other crops, they parts of the state. Although the disease has appear to be host specific, i.e., the grape strain been found in all parts of Texas, the risk is does not appear to infect and vice versa. much greater in East Texas, South Texas and along the Gulf Coast. The pathogen is sensi- Grapevines become infected when a sharp- tive to cold winter temperatures and it is be- shooter that carries the bacterium feeds on lieved that vine infection in the High Plains is tender tissue. These vectors are very ef- most probably alone not fatal. In transition ficient at transferring the bacterium during zones such as the Hill Country and North Cen- feeding and infection is likely. It is now known tral Texas, proper site selection and that there are at least thirty of xylem the following strict management guidelines feeding capable of transmitting the dis- can mitigate the risk of PD. For homeowners ease in Texas. Once a grapevine is infected, or small commercial operations these steps are the multiply and colonize the xylem, not practical. In high risk areas, the disease or water conducting tissue of the . This pressure is so high that planting susceptible

Typical Symptoms of Pierce’s Disease Bois' are capable of being heavily infected, supporting very high concentrations of the bacterium, while still growing and producing acceptable crop loads.

Some tolerant varieties may scorch and exhibit typical symptoms of PD under drought or heavy crop loads, but they recover and grow normally the next year. Native species are likewise tolerant or in some cases, resistant, There is a distinction because with resistance, a plant has the ability to suppress the bacterial titer or concentration levels within the xylem tissue. Morphological studies suggest that dif- ferences in xylem architecture are at least one mechanism whereby can keep the bacte- rial numbers down by inhibiting movement between xylem vessels but tolerant or even resistant grapevines often carry the disease Distribution and risk of Pierce’s Disease in Texas. and are capable as serving as sources of the varieties is simply not recommended. There disease for further spread by sharpshooters. are, however a series of species or varietal Our strong recommendation is that susceptible types that are not susceptible to PD and can be cultivars be grown completely isolated from grown without risk from that pathogen. wild or plantings of resistant/tolerant grape cultivars. Grapevine species and varieties vary widely in their susceptibility to PD, and most European, PD Tolerant & Resistant Varieties American and French-American Although the cause of vine death from PD was not known to him, T.V. Munson realized that utilizing grape parents that survived local con- ditions was important in creating new, im- proved adapted grape varieties. Many, but not all of Munson's varieties are indeed tolerant of PD. While some of these varieties are com- monly utilized in home , they may not produce a of commercial acceptability by today's standards. The most widely planted of these include 'Lomanto', 'Wine King', 'Beacon', 'Edna', 'Ellen Scott' and 'Carman'. 'Champanel' is commonly used for jelly and is perhaps the most widely propagated of all of Native Texas Grape Species Such as Munson's varieties. Some of Munson's highest berlandieri are Tolerant to Pierce's disease quality wine varieties are being included in on- going evaluation trials and will be evaluated varieties are susceptible to it. Once a suscepti- for wine quality relative to other tolerant varie- ble variety is infected, there is no known, ap- ties. In the 1930's, grape variety trials in the proved method of treating the infection and Winter Garden area of Texas identified 'Black the disease will most probably be fatal to the Spanish' and 'Herbemont' as resistant to "vine vine. There are different mechanisms among disease" which we now know as PD. grapevines that do not die from PD. Some va- Across the Gulf Coast, commercial wineries rieties such as '' and 'Blanc du have been established using new resistant/

2 tolerant varieties produced by numerous pub- pathogens, the loose cluster architecture lic and private breeding programs. In many makes it less prone to sour rot complex than southeastern states, some wineries make wine more tight clustered varieties. 'Blanc du Bois' exclusively out of muscadine grapes. High in typically ripens in early July along the Texas antioxidants, muscadine are generally Gulf Coast. finished with relatively high residual . While many consumers enjoy and appreciate 'Black Spanish'- Also known as 'Lenoir' and the distinct flavor of these wines, the market 'Jacquez', 'Black Spanish' is considered the for muscadine wines is generally limited on current highest premises sales and local distribution. quality red wine The most widely planted PD tolerant varie- grape variety that is ties that also have commercial wine appeal are tolerant to PD. The 'Blanc du Bois' and 'Black Spanish'. parentage and his- tory of 'Black Span- 'Blanc du Bois'- Released in 1988 by the ish' are a subject of University of , this variety is currently debate, and some perhaps the highest quality named winegrape believe its history goes back several hundred years.

We do know that 'Black Spanish' has produced high yields under severe PD pressure in South Texas since 1889. Vines of 'Black Spanish' are moderately vigorous, and clusters are large and compact with small berries. Juice from 'Black Spanish' is very highly pigmented high in tannins and acidity lending some wine makers to use juice for pro- duction of high quality port style wines. 'Black variety that has resistance to PD. This grape is Spanish is also used for red wine production, the result of a cross made in 1968 by Dr. John but enologists work to come up with winery Mortensen which was selected as H18-37 for techniques to deal with the overpowering acid- further evaluation in 1974. It has a complex ity. While 'Black Spanish' is typically grown lineage which includes , smal- successfully on its own roots, it is subject to liana, simpsoni, labrusca and an unknown iron in alkaline . 'Black Spanish' open-pollinated selection thought to be V. typically ripens in mid to late July in Texas lincecumi. coastal regions. 'Favorite' is another variety very similar to, and reportedly is an open polli- In addition to being resistant to Pierce's dis- nated seedling of 'Black Spanish'. Some con- ease, 'Blanc du Bois' has reported resistance to sider the fruit to be of superior quality, but , Isariopsis leaf blight and grape commercial availability of 'Favorite' is quite leaf folder. 'Blanc du Bois' averaged approxi- limited. mately 5.5 tons per acre under initial evalua- tions and ripened in hot climates with good 'Victoria Red'- A recent joint release by the acid retention. Clusters average 133 grams University of Arkansas, Tarkington with 45-55 berries per cluster which average and Texas AgriLife Extension Service, Victoria 2.9 grams each. Berries are round, light green, Red is a PD tolerant, seeded table grape that slipskin, with a pleasant flavor. While produces good yields of high quality attractive 'Blanc du Bois' is susceptible to other fungal fruit. Evaluated as Arkansas 1475, ‘Victoria

3 aestivalis. 'Herbemont' has long been valued as a reliable producer of wine grapes and the vines are resistant to PD, and sev- eral fungal pathogens. Along with 'Black Spanish' this variety has been heavily relied upon by Val Verde winery for the production of port wines and is also used at the Maderia win- ery at Parras, Coahuila and at the Ferrino Win- ery at Cuatro Cienegas, Coahuila. Herbemont has also been referred to as the "brown grape" throughout the southeast and produces clear juice for . While this variety has been widely used for perhaps 200 years, there ‘Victoria Red’ is little written record comparing wine quality Red’ was bred in 1971 and is the result of a to that of modern cultivated varieties. cross between Ark 1123 X ‘Exotic’. Although its paternal parent (‘Exotic’) is purely Vitis vi- Other Resistant/Tolerant Varieties nifera, the female parent is a derivation of Other PD resistant or tolerant vines are avail- largely French-American Hybrids produced in able such as 'Miss Blanc', 'Miss Blue', 'Mid- France in the late 1800’s. While neither of the South', 'Orlando' 'Seedless', 'Roucaneuf', parents exhibit resistance or tolerance to 'Daytona', 'Conquestador', 'Stover' and 'Lake Pierce’s disease, there are several ancestors Emerald'. While these can be grown without within the complex lineage of Ark 1123 that fear of loss due to PD, the ability of these varie- have repeatedly been shown to exhibit sus- ties to successfully compete in the commercial tained field tolerance to Xylella fastidiosa. marketplace is questionable. There are how- Tolerant ancestors include ‘Villard Blanc’ (S.V. ever at least two ongoing breeding programs 12-375), ‘Jacquez’ (‘Black Spanish’, ‘Lenoir’), using classical techniques that are producing ‘Herbemont’, as well as the native Texas spe- tolerant winegrape seedlings that are under cies . evaluation in Texas.

'Victoria Red' has survived PD for over 25 Of special note is the important finding of Dr. years with extremely high PD pressure at Tark- Andy Walker, grape breeder at U.C. Davis, that ington Vineyards near Victoria and has pro- all of the genes for PD resistance in the wild duced reliable crops of high quality fruit. species are all located on a sin- While the primary value of this variety is for gle locus. This means that by using marker as- home fresh fruit production, this variety may sisted selection, the time needed to produce well have a place as a neutral blending wine and screen seedlings that are resistant has grape. With soluble solids up to 25º , Vic- been greatly reduced. Dr. Walker has pro- toria Red may help Gulf Coast wineries source duced a number of breeding lines currently a higher portion of their fruit from local vine- under evaluation in that have 87%- yards. 97% vinifera parentage. Seven of these 87% vinifera lines are currently under evaluation in 'Herbemont'- Bred Texas with the intention of identifying resis- and propagated by tant varieties without the color and flavor flaws Nicholas Herbemont associated with American varieties. (1771-1839) of South Carolina and France, 'Herbemont' is pur- portedly a hybrid of Vitis vinifera, borquiniana, and

4