UC Agriculture & Natural Resources Agriculture

Title Cooperative efforts contained spread of Pierce's disease and found genetic resistance

Permalink https://escholarship.org/uc/item/57w8t02n

Journal California Agriculture, 68(4)

ISSN 0008-0845

Authors Bruening, George E Kirkpatrick, Bruce C Esser, Thomas et al.

Publication Date 2014

Peer reviewed

eScholarship.org Powered by the California Digital Library University of California MANAGING NEWLY ESTABLISHED PESTS AND DISEASES

Cooperative efforts contained spread of Pierce’s disease and found genetic resistance by George Bruening, Bruce C. Kirkpatrick, Thomas Esser and Robert K. Webster

An outbreak of Pierce’s disease of grapevine in the Temecula Valley in the late 1990s ierce’s disease (PD) was not new was one in a decades-long series of sporadic appearances of this infection in California. to California in 1999, when its characteristic scorching symptoms However, the new outbreak was qualitatively different because of the rapidity with P suddenly and severely devastated several which it spread in the and its appearance almost simultaneously at distant hundred acres of grapevines in the Tem- locations. The causative agent of Pierce’s disease is the bacterium , ecula Valley, affecting a quarter of the and the distinct characteristics of the Temecula Valley outbreak were traced to the region’s . In the early 1880s, PD, then referred to as Anaheim disease, deci- establishment of a new insect vector in California, the glassy-winged . mated 30,000 acres of vines near Anaheim Intensive and collaborative efforts among government agencies, industry and research and Pomona. Newton B. Pierce, a special institutions over 15 years have successfully contained the disease, and given scientists agent of the U.S. Secretary of Agriculture, time to discover promising long-term potential solutions through genetic resistance. responded to this event as the first profes- sional plant pathologist in California. He skillfully eliminated explanations other than disease but was not able to identify the causative agent. In the late 1880s,

Jack Kelly Clark Jack Kelly the disease damaged vineyards in Napa County, and there were severe outbreaks in Southern California in the 1930s and 1940s. Between 1994 and 2000, grapevines on over 1,000 acres in Northern California were affected, resulting in $30 million in damage (Webster and Nation 2000). The causative agent of PD was long thought to be a virus. The disease actu- ally is caused by a strain of the bacterium Xylella fastidiosa (Davis et al. 1978). Strains of this bacterium also inflict damage on many other plant species, including al- mond, , elm, , , oleander, stone and sycamore. The 1999 out- break in the Temecula Valley was unique, alarming and characterized by rapid and long-distance spread of PD in the vine- yard, resulting from the establishment of a new vector in California, the glassy- winged sharpshooter (GWSS; Homalodisca vitripennis). Further spread of GWSS would place at risk California’s $3 billion crop, $60 billion in associated activ- ity, and $3 billion in fruit, nut and orna- mental crops. Epidemiology of PD X. fastidiosa is transmitted in the field by -feeding insects, especially

Online: http://californiaagriculture.ucanr.edu/ PD symptoms on a red grape variety, showing progressive foliage discoloration, irregular bark maturity and petioles without leaf blades. The Temecula Valley PD outbreak in 1999 triggered an landingpage.cfm?article=ca.v068n04p134&fulltext=yes emergency response to save the and grape industries. doi: 10.3733/ca.v068n04p134

134 CALIFORNIA AGRICULTURE • VOLUME 68, NUMBER 4 sharpshooters (family Cicadellidae, sub- quickly than others (Hopkins and Purcell family ) and related insects 2002). Muscadine varieties (V. rotundifoli a) such as spittlebugs (family Cercopidae) and certain hybrids, especially those (Hopkins and Purcell 2002). Insect vec- that are endemic to , such tors acquire X. fastidiosa from infected as V. labrusca X V. vinifera (Concord grape), plants; some plants are much more effec- support only very low X. fastidiosa titers, tive sources of the bacterium than others, which do not affect fruit quality or kill depending on vector feeding preferences the vine. and patterns of X. fastidiosa accumula- The incidence and severity of PD in tion and spread in the plant (Purcell and California vineyards have been cyclic Saunders 1999). Ingested X. fastidiosa at- since the first record of PD in Anaheim taches to the sharpshooter’s mouthparts, and Pomona in the early 1880s. A PD epi- where it multiplies. Transmission to demic occurred from 1933 to 1940 in the healthy plants occurs when the infected Central Valley, where diseased vineyards vector feeds and egests the bacterium were often located next to weedy alfalfa into the plant’s xylem. Plant symptoms, fields, which were breeding sites for green if any, appear weeks to months later. All (Draeculacephala minerva) and red-headed Clark Jack Kelly GWSS adults caught in a yellow sticky trap. In nymphal stages of the sharpshooter can (Xyphon fulgida) sharpshooters (Hopkins areas infested with GWSS, trap counts indicate acquire X. fastidiosa, but nymphs lose the and Purcell 2002). The blue-green sharp- when insecticides should be applied to citrus bacterium when they molt, because the shooter (BGSS; Graphocephala atropunctata), groves located near vineyards. mouth lining is shed during molting. If a very efficient vector of PD, was largely the sharpshooter acquires X. fastidiosa responsible for the severe outbreaks of PD economically important pest of grape- as an adult, it remains infective for the that have occurred in the coastal regions vines in its own right (Andersen et al. remainder of its life (Hopkins and Purcell of Northern and Southern California and 2003), its establishment greatly increased 2002; Purcell and Finley 1979). in the interior areas of Napa and Sonoma the incidence and severity of PD in the PD is most prevalent in grape-growing counties (Redak et al. 2004; Webster and viticultural regions of Southern California regions of the Southern U.S. states, Mexico Nation 2000). and the lower San Joaquin Valley. To date, and , in areas that have None of these sharpshooters is a strong GWSS has not become permanently estab- mild winter temperatures. Research has flyer, so the PD infections they cause are lished north of Fresno County, although shown that vines experi- typically limited to an area of a few hun- incipient infestations have occurred mentally infected with X. fastidiosa will dred meters from their overwintering sporadically and have been successfully become pathogen-free if the vines are sites, which for the BGSS are weedy ripar- eradicated thus far (CDFA 2013). subjected to cold temperatures (Feil and ian areas and ornamental landscapes. The epidemiology of PD transmitted Purcell 2001; Lieth et al. 2011). This cold Vineyards can be protected by treating by GWSS differs considerably from the curing phenomenon likely accounts for them with insecticides in the spring in epidemiology of PD spread by the BGSS the lack of PD in viticultural regions such response to BGSS counts in yellow sticky and other native sharpshooters. GWSS, as New York, Oregon, Washington and panel traps (Varela et al. 2001). When surprisingly, is a less efficient vector of higher-elevation vineyards in California, the emerging shoots are short, BGSS- where vines experience cold winter tem- vectored X. fastidiosa can reach the per- GWSS flies farther than other sharpshooters, peratures. A recent model based on cold manent woody tissues of the vines and has a polyphagous diet and can spread PD vine curing data by UC Davis professor Johan cause PD that persists and kills the vines. to vine. It initiates infections on a nearly year- Lieth showed good predictive correlations Inoculation of the green tips of longer round basis. between winter temperatures and the canes later in the season tends to not presence or absence of PD in viticultural result in systemic disease, since regions in California (Lieth et al. 2011). the infected portions of the Global warming is expected to alter crop vines are pruned off (Feil geographical distributions (Weare 2009) et al. 2003). and could reduce the areas currently sub- The glassy-winged ject to cold curing. Where winter tempera- sharpshooter tures have warmed in the Southeastern states, PD distribution has increased GWSS probably (Anas et al. 2008). entered Southern All cultivars of European grapevine, California on im- V. vinifera, are susceptible to X. fastidiosa ported plant material infection. While most varieties eventu- in the late 1980s or ally die from the infection, some varieties early 1990s. While GWSS Jack Kelly Clark are more susceptible and succumb more is not considered to be an

http://californiaagriculture.ucanr.edu • OCTOBER–DECEMBER 2014 135 X. fastidiosa than native California sharp- shooters (Daugherty and Almeida 2009). However, GWSS is a highly polyphagous insect, feeding on a variety of plants to fulfill its nutritional requirements (Varela et al. 2001). It also flies much greater distances than the native sharpshooters. The severe PD losses that occurred in the Temecula region in the late 1990s and early 2000s often occurred in vineyards located adjacent to citrus orchards, which are preferred feeding and breeding hosts of GWSS. PD transmitted by GWSS can rapidly encompass an entire vineyard, Clark Jack Kelly During hot , PD causes leaves to turn brown, typically first at the leaf margins. New infestations and significant PD losses occurred in are met with a rapid response and have been eradicated in Northern California counties. vineyards located a mile or more from citrus orchards. regulations required inspection, treat- implemented in other infested viticultural Unlike native PD vectors, GWSS can ment, monitoring and certification of ship- areas. Removal of diseased vines helped acquire and transmit X. fastidiosa from ments from infested areas. Enforcement reduce the incidence and sources of dis- woody tissues such as 1- to 2-year-old of the regulations is coordinated by the ease in these areas. lignified canes (Almeida and Purcell CDFA and usually performed by the staff Detection. In addition to the GWSS 2003; Almeida et al. 2005), and even spurs of county agricultural commissioners containment activities, annual detection that remain when the dormant vines (CDFA 2001). surveys in agricultural and urban areas are pruned. Thus, The certification program, established were begun to search for new GWSS in- GWSS spreads to ensure that shipments of nursery stock festations and verify that uninfested areas See also: Jetter KM, X. fastidiosa on a were free of GWSS, was effective but remained free of GWSS. Surveys rely Morse JG, Kabashima nearly year-round proved to be labor intensive, expensive primarily on sticky yellow panel traps JN. 2014. The cost of basis and initiates and a significant burden to many grow- deployed in areas deemed at risk of GWSS the glassy-winged chronic infections ers (Redak and Bethke 2003). In response, introduction. Trapping is conducted every sharpshooter to Cali- of vines. Extensive concerted efforts were made to find a year during the warm-weather months, fornia grape, citrus and disease map- treatment that could be relied upon to with some locations being monitored nursery producers. ping done in the minimize the risk of spreading GWSS on year-round. Calif Agr 68(4): 161-167. early stages of the shipments of plant material from infested Rapid response. Discovery of one or http://california Temecula epidemic areas. While adult and nymphal GWSS more GWSS in a new area triggers rapid agriculture.ucanr.edu/ showed that GWSS were found to be fairly susceptible to response activity by the CDFA, which landingpage.cfm? can spread X. fas- insecticide treatments, the egg masses consists of intensive visual survey and article=ca.E.v068n04 tidiosa vine to vine. of the insect, embedded in the foliage deployment of more traps to determine if p161&fulltext=yes Other PD vectors of plants, were not (Grafton-Cardwell et a new infestation exists and, if so, where tend to introduce al. 2003; Redak and Bethke 2003). Trials its boundaries lie. New infestations are the bacterium from conducted by researchers at UC Riverside treated with insecticides applied primar- infected nongrape- eventually identified two insecticides ef- ily to preferred host plants of GWSS to vine sources outside the vineyard rather fective against all GWSS stages. Based on eradicate the infestation (CDFA 2013). than from chronically infected vines the trial results and beginning in 2008, Outreach. Outreach plays an important (Varela et al. 2001). the Nursery Stock Approved Treatment role in GWSS containment and suppres- Protocol (Kabashima et al. 2011) became sion efforts. Outreach activities, including Preventing spread of GWSS an optional substitute for the certification meetings, mailings and media pieces pre- After the magnitude of the threat from program. pared by CDFA, UC, counties and outside the Temecula PD epidemic was realized, In large grape production areas that contractors, are aimed at the affected in- the California Department of Food and were already infested with GWSS, such dustries and the general public to inform Agriculture (CDFA) put in place a success- as portions of Kern, Riverside and Tulare them of the new pest threat in California ful four-pronged program: containment, counties, area-wide trapping and treat- and the new programs and activities be- detection, rapid response and outreach. ment programs for reducing GWSS num- ing conducted to address it. These efforts Containment. Within the infected ar- bers were implemented and evaluated. In have helped gain compliance with new eas, the CDFA promulgated regulations these programs, coordinated insecticide shipping requirements and enlisted assis- aimed at interdicting likely pathways treatments were applied primarily to tance from the public in finding new in- of GWSS spread from infested areas of citrus and, on occasion, to windbreaks, festations and preventing further spread Southern California. This involved regu- when trap counts revealed GWSS popu- of GWSS. lating shipments of general nursery stock, lations at or above damage thresholds Success of the current four- bulk and (later) bulk citrus. The (CDFA 2005). Similar programs were later pronged program is evidenced by two

136 CALIFORNIA AGRICULTURE • VOLUME 68, NUMBER 4 observations: The GWSS-infested area in being conducted on an ongoing basis collected in the Southern U.S. states and California this year is only slightly larger (CDFA 2001, 2013). northern Mexico (Walker and Riaz 2012). than the area infested in 2002 (fig. 1), and The natural enemies predominantly Progeny of interspecific (i.e., interspecies) 17 infestations found outside this area to used against the sharpshooter are tiny crosses and backcrosses to V. vinifera were date have been eradicated. The success of mymarid wasps in the genus Gonatocerus, evaluated for a spectrum of horticultural the GWSS control program shows it can which lay their eggs inside the eggs of and quality traits in addition to resis- be a model for responding to other pest the sharpshooter. Approximately 2.4 mil- tance to X. fastidiosa (Viana et al. 2011). invasions. However, the potential remains lion of these wasps have been released Aggressive , which forced for GWSS populations to flare up, as in California to date (CDFA 2013). These flowering of 2-year-old seedlings, and ap- evidenced by increased trap counts, and efforts have involved a collaborative re- plication of DNA marker technology gen- spread to new areas or resistance to cur- sponse from CDFA (Larry Bezark, David erated progeny of the fourth backcross, rent control methods could develop, re- Morgan, Charlie Pickett), UC Riverside expected to be genetically 97% V. vinifera, quiring that program measures continue (Ali Al-Wahibi, Mark Hoddle, Nick Irvin, in only 10 years. Test-size lots of wine and prompting recent initiation of studies Rodrigo Krugner, Joseph Morse, Leigh have been made from grapes of previous on resistance management. Pilkington, Serguei Triapitsyn) and USDA generations and currently are being made While insecticide treatments have (Greg Simmons). from fourth backcross generation selec- proven critical to keeping GWSS popula- tions. Release of PD-resistant varieties Genetic approaches to combating PD tions low and preventing the spread and with a range of wine styles is anticipated establishment of GWSS in new areas of Genetic resistance is generally re- (Walker and Tenscher 2012). The breeding California, biological control is also used garded as the most reliable control program continues. as part of an integrated management ap- measure for a readily transmitted plant Efforts in other laboratories have trans- proach. Biological control efforts began in disease. Although there is apparent varia- ferred specific genes from nongrapevine the late 1990s, when explorations for natu- tion in the susceptibility of European sources, referred to as transgenes, into V. ral enemies were conducted in the native grapevine (V. vinifera) varieties to X. vinifera. The advantage of the transgenic range of GWSS (Triapitsyn et al. 1998). fastidiosa, all succumb to PD (Hopkins approach is that it greatly increases the The Temecula PD outbreak stimulated and Purcell 2002). The research group of number of sources of resistance beyond additional searches for biological control Andrew Walker at UC Davis discovered what is available in conventional breed- agents, and testing, rearing, release and both apparently single-gene and multiple- ing. Ten years ago, only a few sketchy monitoring of natural enemies are now gene resistance in other Vitis species notions were available on how to create

2002 2014

Butte

Sacramento

Madera Santa Clara Santa Clara Fresno Fresno Tulare Tulare

Kern Kern Santa San Bernardino Santa San Bernardino Barbara Ventura Los Barbara Ventura Los Angeles Angeles

Orange Riverside Orange Riverside

San Imperial San Imperial Diego Diego GWSS-infested area

Fig. 1. Areas of California infested by GWSS in 2002 and 2014. At the end of 2002, GWSS was confined mostly to Southern California counties, with minor infestations in three Northern California counties. The Southern California infestation in 2014 is slightly expanded compared to the infestation in 2002, but some Northern California infestations have been eradicated. Other infestation maps are available at cdfa.ca.gov/pdcp/map_index.html.

http://californiaagriculture.ucanr.edu • OCTOBER–DECEMBER 2014 137 transgenes capable of interfering with use could be grafted onto the transgenic clever experimental approaches for devel- X. fastidiosa infection of grapevine or the line and be at least partially oping transgenic resistance to X. fastidiosa mechanisms on which they might oper- protected against X. fastidiosa. in grapevines. ate. Infecting X. fastidiosa bacterial cells The transformed lines that have been Fusion of two proteins. One straightfor- reside not in the living cells of the plant, examined closely are indistinguishable ward approach to reducing the titer of where a transgene product normally from the untransformed lines from which X. fastidiosa in grapevine xylem is to would accumulate, but in the xylem, the they were derived (Dandekar et al. 2011; discover or develop a protein capable array of dead cells that form the vascular Lindow et al. 2014), suggesting that the of killing or preventing the increase of elements responsible for conducting water vines have the quality and horticultural X. fastidiosa cells and then to deliver that and minerals from the roots into the aer- traits of the untransformed lines. This protein to the xylem. A research group ial parts of the plant. Responding to this result is expected because the transfor- headed by Abhaya Dandekar at UC Davis challenge, researchers not only identified mation process introduces only a minute and including Goutam Gupta of Los various genetic elements that encode change in the plant genome. In commer- Alamos National Laboratory conceived molecules that restrain the accumulation cialization, combinations of several trans- the approach of fusing two proteins, each and/or spread of X. fastidiosa but also ele- genes acting through distinct biochemical with some activity against X. fastidiosa, ments that deliver these molecules to the mechanisms of action likely would be into a single, xylem-targeted protein. xylem. Importantly, several of the mol- introduced into a grapevine line to obtain One protein of the fusion pair binds to a ecules were shown to cross graft unions at least additive resistance effects and to specific protein that is abundant on the and to confer, as a transgenic rootstock, greatly reduce the chance that a variant surface of the X. fastidiosa cell. The other protection to a grafted nontransgenic X. fastidiosa would be able to overcome re- protein breaches the X. fastidiosa cell scion. Rootstock-conferred resistance has sistance. The following paragraphs sum- membrane, thereby killing the bacterial obvious versatility: Varietal scions now in marize five mechanistically diverse and cell. Both proteins killed X. fastidiosa cells

Coordinated response to PD involves growers, scientists and government he academic and government research on GWSS and PD 1996 Treceived support from the state’s and enology UC ANR forms Viticulture Consortium (VC), funded by a grant industries and even local government before and during the from USDA Cooperative State Research, Education, and Extension Temecula Valley outbreak. Industry organizations partner- Service (USDA CSREES, now USDA NIFA, National Institute of Food ing with CDFA and UC Division of Agriculture and Natural and Agriculture). Resources (UC ANR) in these efforts included the American Report of GWSS establishment in Southern California Vineyard Foundation, the California Table Grape Commis- is published. sion, the California Raisin Board and the California Rootstock Commission. UC ANR and CDFA provided 1997 coordination to prioritize research, Industry-matched state funds initiate the California Competitive avoid duplication and maximize Grant Program for Research in Viticulture and Enology (CCGPRVE). the collective benefits of the programs. Since 1999, USDA 1998 has provided about 75% of Search for biological control agents for GWSS begins. the funding for PD control 1999 and research, and the state of California, industry and Temecula Valley vineyards show severe damage from PD; GWSS is UC have provided the recognized as the vector. rest. California legislation Riverside County declares emergency; the county and city of initiated a statewide as- Temecula each contribute $125,000 for research. sessment on wine grapes UC appoints Pierce’s Disease Research and Emergency Response to support research and Task Force to identify strategies for combating PD. related activities, raising CDFA appoints task force with members from UC, California State about $46 million to date University, CDFA, county agricultural commissioners, USDA and (Tumber et al. 2014; Wig- industry to identify PD/GWSS research priorities. gins 2001). The timeline here Jack Kelly Clark Jack Kelly highlights some of the key CA Assembly Bill 1232 provides $2.25 million over 3 years to be events in the efforts to contain matched by $0.75 million in industry funds for PD/GWSS research; and find solutions to the PD out- the CDFA competitive grants program is funded. break in California.

138 CALIFORNIA AGRICULTURE • VOLUME 68, NUMBER 4 in culture, but the fusion protein was sig- protein to be secreted into the xylem, in the plant, whereas spread of mutants nificantly more potent than either protein where infecting X. fastidiosa cells colonize that overproduce XfDSF is severely re- component alone. Grapevines expressing the vine. Greenhouse-grown plants were stricted (Chatterjee et al. 2008). the fusion protein showed significant pro- found to have reduced disease symptoms Transfer of a gene whose product cata- tection against PD (Dandekar, Gouran et compared to unaltered grapevines when lyzes XfDSF synthesis should result in ac- al. 2012). inoculated with a high dose of X. fastidiosa cumulation of XfDSF even in the absence HxfA protein. Bruce Kirkpatrick’s (Kirkpatrick et al. 2012). of X. fastidiosa and, after inoculation with laboratory at UC Davis identified a pro- XfDSF, pathogen confusion. Steven X. fastidiosa, should constrain movement tein of X. fastidiosa, HxfA, which, when Lindow and his research associates at UC and accumulation of X. fastidiosa and re- inactivated, surprisingly led to increased Berkeley intensely investigated intercel- duce PD symptom extent and intensity. virulence of the bacterium (Guilhabert lular communication of X. fastidiosa and These expected results have been ob- and Kirkpatrick 2005). This result sug- applied their findings to suppress the served (Lindow et al. 2012, 2014). gests that, when active, HxfA suppresses spread of the bacterium in the plant using Programmed cell death. The char- virulence. Perhaps a grapevine line that a phenomenon they refer to as pathogen acteristic scorching symptoms of PD produces HxfA could reduce PD severity confusion. X. fastidiosa secretes a specific were shown by the laboratory of David by decreasing the virulence of infecting 14-carbon fatty acid and possibly other Gilchrist at UC Davis to be an example X. fastidiosa, and infecting X. fastidiosa similar molecules as diffusible signal fac- of the phenomenon known as genetically would be less successful at inducing PD tors (XfDSF). As X. fastidiosa populations programmed cell death, where the symp- than in unaltered vines. Grapevine plants grow, the concentration of XfDSF around toms resulted from a reaction of the plant producing full-length or truncated ver- the cells increases. Compared to the unal- to the presence of a bacterium (X. fastidi- sions of HxfA were constructed. The tered bacterium, X. fastidiosa mutants that osa) rather than directly to an action of genes were designed to cause the HxfA fail to produce XfDSF spread more readily that bacterium (Gilchrist et al. 2007). This

2000 2004 UC is awarded USDA CSREES grant of $2 million to establish a CDFA and UC competitive PD/GWSS research programs combine competitive grants program for PD/GWSS research; annual fund- their proposal review processes. ing was renewed eight times. CDFA-requested report “California Agricultural Research Priorities: UC establishes Pierce’s Disease Competitive Grants Program. Pierce’s Disease” is published by National Research Council of the CA Senate Bill 671 provides funds for a coordinated statewide ef- National Academies. fort against PD/GWSS. Number of GWSS biological control agents released in California Federal government declares emergency and provides $22.3 mil- since 1999 exceeds 1 million. lion for GWSS containment and PD research. 2005 First GWSS infestation is found outside the generally infested grape growers vote to continue statewide PD/ Southern California area, in Contra Costa County; eradication ef- GWSS wine grape assessment. forts begin. 2008 CDFA adopts emergency regulations to prevent spread of GWSS on shipments of nursery stock, bulk grapes and (later) citrus. Nursery Stock Approved Treatment Protocol established to re- duce need for GWSS inspections. 2001 2010 CA Assembly Bill 1394 creates the Pierce’s Disease and Glassy- Winged Sharpshooter Board and an assessment on wine grapes California wine grape growers vote again to continue statewide to fund PD/GWSS research and related activities; this assessment PD/GWSS wine grape assessment, with option to support re- raised $46 million through February 2014. search and outreach on other wine grape pests and diseases. First area-wide management program begins in Kern County, 2011 testing methods for controlling PD and GWSS in large and diverse Last CCGPRVE-supported project completed, and the agricultural areas. program ends. First annual PD/GWSS research symposium takes place. 2013 2002 Last projects funded by USDA-UC and VC are completed; these GWSS infestation found in Contra Costa County in 2000 is de- programs end. clared eradicated, marking the first successful eradication of a Industry-funded CDFA competitive grants program continues, localized GWSS infestation. with its proposal review process now conducted under UC ANR’s Unified Grant Management for Viticulture and Enology. c

http://californiaagriculture.ucanr.edu • OCTOBER–DECEMBER 2014 139 Varietal scions now in use could be grafted onto the transgenic rootstock line and be at least partially protected against X. fastidiosa.

protection against X. intractable in molecular terms. Over the fastidiosa. Protection years, research projects were supported at and level of PGIP 16 universities and at several government accumulation were laboratories, and the continued funding positively correlated from various sources, including grower- in different trans- voted assessments (see sidebar, pages formed grapevine 138–9), resulted in numerous advances in lines (Aguero et al. our understanding of the biology of the 2005). PGIP is natu- disease and the development of effective rally targeted to the control measures. xylem, and PGIP- The entire genome sequence of Gregory Urquiaga generating X. fastidiosa became available, and pro- UC Davis plant scientist Abhaya Dandekar and colleagues have fused protected grafted cedures for creating mutants of the two genes to engineer resistance to Pierce’s disease of grapevines. nontransgenic scions. bacterium and introducing new genes The untransformed were developed and applied (Guilhabert research group searched a large collection scion was demonstrated to accumulate et al. 2001; Guilhabert and Kirkpatrick of grapevine genes for the ability of spe- PGIP from its PGIP-transgenic rootstock, 2003; Newman et al. 2004; Van Sluys et cific nucleotide sequences to confer pro- suggesting that transported PGIP is the al. 2003). Genetic variation in X. fastidiosa tection against programmed cell death in actual agent of protection in the scion was characterized as to its origins and tomato roots. Two of these grapevine nu- (Dandekar, Gilchrist et al. 2012; Labavitch its determination of host range (Nunney cleotide sequences, when transferred back et al. 2012). 2011; Nunney et al. 2013). Individual into grapevine, suppressed PD symptoms Tests of transformed grapevine lines events in the association of X. fastidiosa and prevented death of the X. fastidiosa- were performed first in the greenhouse, with the sharpshooter and the establish- inoculated plants (Harvey et al. 2008). and outdoor trials of these newly devel- ment of feeding sites by the sharpshooter Moreover, the bacterial titer was reduced oped grapevine materials were begun in have been revealed (Almeida and Purcell by 4 to 6 orders of magnitude relative to March 2010. The field trials are expected 2003; Almeida et al. 2005; Son et al. 2012). the titer in untransformed control vines, to valuable information on the feasi- The arrays of grapevine messenger RNAs which died in 2 to 3 months. In the trans- bility of developing these approaches into (responsible for directing the synthesis formed plants, X. fastidiosa titers were re- commercial applications (Gilchrist et al. of proteins) that accumulate under vari- duced to a level that should result in only 2012; Miller et al. 2012). ous situations were characterized and rare or no acquisition by the sharpshooter. revealed grapevine genes that specifi- Research advances One of the nucleotide sequences, when in- cally respond to X. fastidiosa infection but troduced into the rootstock only, was able The seriousness of the GWSS-borne not to drought (Choi et al. 2010, 2013). In to protect untransformed scions (Gilchrist X. fastidiosa threat to the California wine cold curing, X. fastidiosa was found to and Lincoln 2009). and grape industries was realized early be cleared not by the effects of low tem- PG-inhibiting protein (PGIP). The in the Temecula Valley PD outbreak, and peratures alone but by the grapevine’s X. fastidiosa genome has one gene for effective cooperation between federal, response to the cold (Feil and Purcell the enzyme polygalacturonase (PG), an state and county agricultural agencies, in- 2001; Lieth et al. 2011). Obviously, these enzyme that cleaves homogalacturonan, dustry groups, and UC followed. Actions research advances would not have been a major component of the intercellular taken to combat the Temecula Valley PD possible without the sources of research matrix that joins the walls of adjacent epidemic and prevent its spread were rap- support indicated above. The new discov- plant cells. A X. fastidiosa strain with an idly mounted, and funding from federal, eries have elevated the bacterium, the in- inactive PG was unable to move long dis- state and industry sources has supported sect vector and the plant host close to the tance in the inoculated plant or to induce both control measures and basic and ap- level of a model research system and cre- PD symptoms (Roper et al. 2007). UC plied research. A summary of current ated a foundation for new management Davis researchers Abhaya Dandekar, John research and control costs associated with strategies in the future. c Labavitch and Ann Powell lead research PD appeared recently (Tumber et al. 2014), groups that have demonstrated interfer- and the sidebar below indicates some of ence with X. fastidiosa accumulation in the research expenditures. plants by the action of a PG-inhibiting Of the biological actors in the epidemic G. Bruening, B.C. Kirkpatrick and R.K. Webster are all Professor Emeritus, Department of , protein (PGIP). The PGIP from pear fruit (X. fastidiosa, GWSS and grapevine), UC Davis; T. Esser is Special Assistant, Pierce’s Disease was found to be effective in inhibiting none was regarded in 1999 as being Control Program, California Department of Food and bacterial PG. The pear PGIP gene was well characterized in research terms, Agriculture, Sacramento. moved into grapevine, where it provided and all seemed at the time to be almost

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