Wednesday, September 21, 2011



                               STEPHEN J. KREBS

The grape phylloxera, Daktulosphaira vitifoliae (Fitch), (Hemiptera: Homoptera: Phylloxeridae), is an aphid-like insect that attacks the roots and the leaves of plants in the genus Vitis.  It was first described in 1854 from vines in New York State by Asa Fitch, who named the insect Pemphigus vitifolii.  It was then reclassified into the genus Phylloxera (Mayet, 1894) but because the grape phylloxera differs morphologically from other phylloxera species it was re-assigned to its own genus.  Outside the United States, Viteus is an accepted synonym for the older term Daktulosphaira.  Numerous other names appear in the literature (Russell, 1974). 

The basic biology of phylloxera was established in the 1870s by C. V. Riley, State Entomologist in Missouri (Riley, 1871, 1872, 1873, 1874, 1876).  He found that in its native North American range and in other summer-humid climate areas, phylloxera has a complex life cycle, feeding on both the root system and the aerial portion of the vine (Figure 1).  The root feeding forms are all oviparous parthenogenic females.  Some of the eggs these females produce are pre-destined to  become winged adults.  In their fourth instar the alates emerge from the soil and molt to the winged type.  In this form they are highly mobile (Riley, 1876).  The winged adult, which does not feed, lays eggs that hatch into male and female insects.  These males and females, which also do not feed, molt four times, mate and produce the so-called winter egg.  Only fundatrix females hatch from the winter eggs, their feeding inducing galls to form on the vine leaves.  They develop and lay eggs which will produce females.  The offspring of the fundatrix females eventually exit from the galls to form new galls.  Some may return to the soil to live on the roots.  Infestations are spread by both the movement of the winged form above ground in regions where they are fertile, and by the crawler form, a first instar female that can move short distances above or below ground (Riley, 1874) or, when they are above ground, short or long distances in wind (Granett, personal communication, 1995).  Riley confirmed that the insect damaging vines in France and California was the same phylloxera native to the eastern United States (Riley, 1872; Appleton, 1880; Ordish, 1987).  He also confirmed that American Vitis species were resistant to phylloxera and were seldom killed by the insect (Riley, 1880).

In California and other dry-summer climates, the phylloxera life cycle is truncated.  The insect is found on the roots as an oviparous parthenogenic female.  The development of the winged form is often observed under these growing conditions, but it is not known to be fertile and therefore no sexual forms or winter egg is produced and there is no leaf-galling.  The lack of the sexual cycle is thought to limit the genetic diversity of the phylloxera population (Davidson and Nougaret, 1921).

Phylloxera may damage grapevine roots by feeding on either new root tips or on older root tissue.  Feeding on new root tips causes a small gall called a nodosity to develop at the feeding site.  Feeding on older roots causes the formation of an abnormal roughened swelling called a tuberosity.  The formation of tuberosities is more serious because it leads to the decomposition and death of the damaged root (Millardet, 1892).

Phylloxera damage to the roots of the grapevine results in a general weakening and the eventual death of susceptible plants.  Vegetative symptoms include reduced cane growth, short internode length, an absence of actively growing shoot tips in the spring and premature leaf fall.  Crop yield is reduced because the berries are small and few clusters are produced.  The symptoms become increasingly severe over several seasons.  In the field, a circular pattern of decline radiating from the point of first infestation may occur (Riley, 1874; Bioletti, 1901; Davidson and Nougaret, 1921; Husmann, 1910).

In North America phylloxera coevolved with the indigenous Vitis species.  The resistance developed by some American Vitis species limits the root damage caused by the insect.  Different levels of resistance to both leaf and root damage are found among the Vitis species (Riley, 1874; Millardet, 1892; Viala and Ravaz, 1903; Boubals, 1966).  Vitis vinifera has susceptible roots but is resistant to leaf galling (Wapshere and Helm, 1987).  It is the species from which most commercial grape cultivars have been selected.  Accidental importation of phylloxera led to the catastrophic destruction of V. vinifera vineyards throughout Europe, California and most other world viticultural regions in the late nineteenth century (Stevenson, 1985; Ordish, 1987).  It is the most important insect enemy of the grapevine worldwide.

The introduction of phylloxera into Europe probably occurred on American vines used in grafting and hybridizing experiments for the control of powdery mildew (öidium), Uncinula necator, which had been accidentally brought into Europe in the mid-1800s from North America (Hewitt, 1988).  The knowledge gained from this work was later applied to the control of phylloxera (Ordish, 1987).  

Phylloxera was found on the roots of grapevines in southern France in 1868 (Planchon, et al., 1868).  Based on vine decline symptoms that had been previously noted there, the actual introduction into France probably occurred in the Rhone Valley around 1862.  The insect spread very rapidly and soon had devastated the viticulture industry in much of the country (Stevenson, 1980). 

In other European countries, phylloxera was found at about the same time.  In Portugal, the first discovery of the pest occurred in 1862.  It had spread through the Douro region by 1872 and was found in most other districts by 1880 (Bleasdale, 1880; Morrow, 1973).  In Spain, the discovery of phylloxera occurred in 1876 in the Mediterranean district of Malaga and infestation had become general in the country by 1888.  In Italy, phylloxera was probably present by 1870.  In Germany, the first damage occurred in 1875 (Ordish, 1987).  In Great Britain, phylloxera was discovered in 1867 (Stevenson, 1985).  Other European countries infested with phylloxera include Turkey, Austria, Hungary, Switzerland, Algeria, Greece, Cyprus and Yugoslavia (Branas, 1962; Daris, 1970; Ordish, 1987).  In Asia, phylloxera is present in Korea and in Japan.  In Central America, the insect is found in Mexico (Anonymous, 1975).

Phylloxera was also introduced into viticultural regions of the Southern Hemisphere in the nineteenth century.  The insect was first detected in Australia in 1875 (Adcock, 1914; Buchanan, 1987).  The introduction into New Zealand occurred in 1885 (Dry and Smart, 1982a, 1982b; Smart and King, 1983).  In South Africa, phylloxera was discovered in 1886 and is now widely distributed throughout the grape growing regions of that country (De Klerk, 1972).  In South America, phylloxera is present in Peru, Brazil and Argentina (Anonymous, 1975).  Olmo (1976) believes it to be native to Venezuela.

Phylloxera created severe economic and social displacement as wine production declined (Eichel, 1975; Stevenson, 1980; de Blij, 1983; Ordish, 1987; Unwin, 1991).  Expensive insecticide applications were devised to control the insect.  Carbon bisulfide was the most effective material tested, but its application was labor-intensive and the effects were short-lived.  Repeated treatments were therefore required.  Many other purportedly insecticidal materials were also recommended, including coal tars, manures, and various fanciful decoctions.  None of these were successful in the control of the insect (Bleasdale, 1880).   Quarantine methods were generally ineffective in controlling the spread of phylloxera.  Growers were warned to practice careful sanitation whenever moving from one vineyard to another, because the insect is readily transported on harvesting bins, on nursery stock and in contaminated soil that becomes attached to vineyard equipment and workers' clothing.  The small size of the pest makes detection difficult (Fox, 1902; Viala and Ravaz, 1903).

Phylloxera was first found on the roots of grapevines in the Sonoma Valley in 1873, at the center of the young California wine industry.  It was to this location that many Vitis cultivars had been introduced before being taken to other growing regions in the state (Pinney, 1984).  As early as 1860, growers had noted vines with symptoms of phylloxera injury (Appleton, 1880).  University of California reports proposed an introduction date of 1858 (Davidson and Nougaret, 1921) or 1852 (Smith and Stafford, 1955).  The insect may have been brought into California directly from the eastern United States (Davidson and Nougaret, 1921), from contaminated sites in Europe (Bioletti, 1901) or on the roots of  the V. vinifera cultivar Mission (Criolla) imported from Mexico (Granett, personal communication, 1994).  Multiple introductions from these sources may have occurred.

Soon after the discovery of phylloxera in Sonoma Valley, the insect was found in adjacent regions.  By 1880, damage to vineyards had become so serious that the California State Legislature passed an act that created the Board of State Viticultural Commissioners and mandated that the University of California develop a department of viticulture.  The phylloxera problem was a primary focus of their activities (Borg, 1991).

Both the Board and the University published information on the insect and documented the rapid spread of the infestation. By 1900, phylloxera was present in all grape growing areas north of the Tehachapi Mountains (Bioletti, 1901).  The rapid spread of the insect caused severe economic damage to the wine industry in the state (Sullivan, 1981, 1982).  Phylloxera has never become a problem in Southern California vineyards, probably because the soils are generally sandy there and inland areas may be too hot for the pest (Granett, et al., 1992).

At first innumerable methods were proposed for the control of phylloxera (Bleasdale, 1880; Wetmore, 1880).  The Board of State Viticultural Commissioners in California published summaries of the most important work on the insect at that time.  Hundreds of articles were listed that describe the biology, damage and incidence of phylloxera, and possible control practices.  Many of these practices involved the application of some material that was purported to have insecticidal properties.  The inaccessibility of the insect on the roots made this approach largely impractical.  The most successful methods proposed included the planting of grapevines on sandy soils, carbon bisulfide soil treatments, the use of water for vineyard submersion during the winter dormancy period and the use of resistant rootstocks. 

From 1885, the use of American Vitis vines for phylloxera-resistant rootstocks became the focus of control efforts.  American vines were evaluated in Europe for phylloxera resistance and viticultural performance.  By comparing the relative development of nodosities and tuberosities on grapevine roots infested with phylloxera, it was found that V. riparia, V. rupestris and V. berlandieri and their hybrids were sufficiently resistant to phylloxera for use in commercial vineyards (Millardet, 1892).  Some crosses were made using the susceptible V. vinifera in an attempt to develop direct producer vines that did not require resistant rootstocks. (Millardet, 1892; Fox, 1902; Viala and Ravaz, 1903).

In California, grape growers began to use the resistant vines developed in Europe.  The first rootstocks planted in California were Lenoir and Herbemont, which are natural hybrids between V. vinifera and American vines (Munson, 1885).  These two rootstocks were quickly destroyed by phylloxera.  The native grape V. californica was used as a rootstock for a short time (Hilgard, 1885a, 1885b, 1886, 1887), but was discarded because of its insufficient phylloxera resistance (Hayne, 1897).  Growers also planted unselected seedlings of V. riparia and V. rupestris.  Many of these seedling rootstocks had insufficient resistance and were killed by the insect (Hilgard, 1886).  Other failures occurred because rootstocks were not well adapted to particular soil conditions (Hilgard, 1887).  It became clear that scientific evaluation of rootstocks for California vineyards was essential (Hayne, 1897; Bioletti, 1906; Husmann, 1910).

During the late 1800s and early 1900s, thousands of hybrid rootstock cultivars were developed and tested by European breeders, mainly in France (Fox, 1902; Viala and Ravaz, 1903).  The genus Vitis is highly heterozygotic (Olmo, 1976) and phenology is not predictable, so it is necessary to test rootstocks under field conditions before satisfactory recommendations can be made.

The results of early French rootstock evaluations and the nature of both specific rootstocks and of general parentage combinations have been summarized by several authors (Hayne, 1897; Fox, 1902; Viala and Ravaz, 1903).  While confirming that the suitable Vitis species for rootstock use were V. riparia, V. rupestris, V. berlandieri and their hybrids, they warned against the use of V. vinifera-American Vitis rootstock hybrids.  Although rootstocks with V. vinifera parentage may be selected which are vigorous, grow on a wide range of soils and are easily propagated, their resistance to phylloxera tends to be unstable.  Numerous failures of such rootstocks are cited (Fox, 1902; Viala and Ravaz, 1903) and the authors state unequivocally that only rootstocks of pure American Vitis parentage can contain a stable resistance to phylloxera.  In France, the use of some V. vinifera-American Vitis hybrid rootstocks declined.  The V. berlandieri x V. vinifera hybrid rootstock cultivars 41B and Fercal are still widely used there (Galet, 1979; Pongrcz, 1983).

The low or unstable phylloxera resistance of V. vinifera-American Vitis rootstock hybrids has been confirmed for many rootstock cultivars by field research trials (Bioletti, 1908; Bioletti, et al., 1921; Jacob, 1938; Loomis, 1943; Jacob, 1944; Lider, 1958a), commercial vineyard experience (Bioletti, 1906, 1908, 1920; Perold, 1927; Galet, 1956; Dalmasso, 1968; Galet, 1979; Pongrcz, 1983) and in laboratory rating studies (Boubals, 1966; Pastena, 1976; De Benedictis and Granett, 1991).

Extensive rootstock testing has been conducted in many other grape growing regions.  In Australia, New Zealand and California the V. vinifera-American Vitis hybrid rootstocks have been widely planted (Hardie, 1977; Clarke and Pollock, 1981; Pongrcz, 1983; Smart and King, 1983; Whiting, et al., 1987; Whiting, 1991; Southey, 1992). This practice is now changing in these locations.

At first, California grape growers were completely dependent on rootstock testing performed in Europe, because most of the phylloxera-resistant rootstocks available in California were developed by European breeders (Hayne, 1897).  After early failures in the reconstitution of phylloxerated vineyard sites, scientific field trials in California were established to determine which rootstocks were best suited to the soil and climate conditions peculiar to the state. 

The first United States Department of Agriculture rootstock trials in California were started in 1902 (Husmann, 1910).  Over four hundred V. vinifera fruiting varieties and almost three hundred rootstock cultivars were tested in several locations.  The rootstocks were inoculated with phylloxera to determine resistance and rated according to their effect on yield and vigor in the scions.  The trials continued until 1939 (Husmann, et al., 1939).  The AxR#1 rootstock was one of a group of rootstocks recommended in 1910 because it was resistant to phylloxera and induced high vigor and high yield in scion varieties grafted onto it (Husmann, 1910).  A similar recommendation for AXR#1 was repeated in succeeding U.S.D.A. reports from these trials (Husmann, 1915, 1930; Husmann, et al., 1939).

Additional U.S.D.A. rootstock trials were established in the 1930s at Oakville in the Napa Valley and at Fresno.  Both sites were infested with phylloxera.  In these trials, rootstocks were judged according to their effect on vigor, yield and fruit quality.  Despite its earlier recommendation, AxR#1 was not included in these U.S.D.A. rootstock tests.  No reason for this omission was given in the reports of the trials (Snyder and Harmon, 1948; Harmon, 1949; Harmon and Snyder, 1952, 1956; Snyder and Harmon, 1956). 
The first University rootstock trial was started in 1900 at the Moffit Vineyard in St. Helena in the Napa Valley.  In a report on this trial, Bioletti (1908) stated that all the rootstocks tested were vigorous, although there is no mention of the phylloxera status of the test site.  He recommended St. George for dry soils and AxR#1 for compact or wet soils, stating that AxR#1, unlike other V. vinifera-American Vitis hybrids, has sufficient resistance to phylloxera.  He also discussed the failure of AxR#1 in some South African vineyards.  He suspected the failures were caused by overcropping, but indicated that no really satisfactory explanation for the death of vines there had been proposed.

The University began testing rootstocks in 1911 at Davis and at Kearney, measuring the effect of rootstock on scion variety vigor and yield in specific rootstock-cultivar combinations.  In 1921, AxR#1 was recommended for limited use by the University because it had produced high yields and high vigor in some of the scion varieties tested.  It apparently had good phylloxera resistance, although no mention of phylloxera conditions at the test locations is included in the report (Bioletti, et al., 1921).

Starting in 1929, Jacob established University rootstock trials in presumably phylloxerated commercial vineyards, using the most promising stocks from previous tests.  Jacob used the V. rupestris St. George rootstock as a standard of comparison at all of these cooperative rootstock trials.  He chose this rootstock because it was the most widely planted rootstock in California at that time and because it was considered resistant to phylloxera.  Jacob published recommendations for AxR#1 prior to his death in 1949, based on good scion vigor and yield in his trials.  He noted that AxR#1 does not have high phylloxera resistance compared to other rootstocks. However, AxR#1 performed well in the trials in spite of its low phylloxera resistance.  Jacob felt that no satisfactory rootstock was available for dry conditions, so he reluctantly recommended St. George for these sites (Jacob, 1938, 1944, 1947; Jacob and Winkler, 1950). 

After the death of Jacob, University rootstock studies were continued by Lider.  Rootstock rating criteria were expanded to include several fruit quality factors in addition to vigor and yield.  By the mid-1950s, University viticulturists had recommended AxR#1 as an all-purpose phylloxera-resistant rootstock while noting that its phylloxera resistance was relatively low compared to other rootstocks.  It became the most widely planted rootstock in the north coast winegrape regions of the state.  The St. George rootstock recommendation was continued for dry sites (Lider, 1957, 1958a, 1958b, 1958c, 1959; Lider and Sanderson, 1959; Kasimatis and Lider, 1962; Lider, 1964; Kasimatis and Lider, 1972; Lider, et al., 1973; Kasimatis and Lider, 1981). 

In 1978 data collected from six of the University rootstock trials established between 1935 and 1941 showed that the AxR#1 vines in these trials were still performing well.  The authors were clearly concerned with the possible failure of this rootstock.  Although the low phylloxera resistance of AxR#1 was noted, they continued to recommend it for planting in the phylloxerated vineyard soils of California (Lider, et al., 1978). 

Insects of a single species may differ in reproduction,  survival and development, behavior, host preference and other traits.  The term biotype has been used broadly to describe such variations within a species (Russell, 1978).  When an insect biotype is partially or completely isolated reproductively from other members of the species as a result of adaptation to a particular host, the more specific term host race is used.  It may be impossible to distinguish host races morphologically from other insects of the same species (Diehl and Bush, 1984). 

Biotypes are common in other aphid species (Eastop, 1973; Russell, 1978).  The complex life cycle and its long coevolution with Vitis should produce biotypes in phylloxera as well (Riley, 1874; Fergusson-Kolmes and Dennehy, 1991, 1993; Hawthorne and Via 1994).  Since phylloxera may injure or destroy susceptible vines, host races are of concern to grape growers.  In order to perform well over the normal lifetime of a vineyard a rootstock must have stable resistance to any possible host races.  If a genetic weakness in a rootstock permits a new host race to arise, the potential for economic damage is great.

The existence of phylloxera biotypes has been demonstrated in many different locations.  As early as 1914, Brner claimed that both morphologically distinct races of phylloxera and strains of the insect that utilized specific rootstock hosts were present in Germany (Brner, 1914).  The occurrence of morphologically different phylloxera biotypes has not been substantiated, but the existence of host races has been demonstrated in tests with various rootstocks (Becker, 1988).

In South Africa, a new host race on the roots of vines developed around 1912.  At first, the AxR#1 rootstock was destroyed by phylloxera only in certain districts and not in others.  This failure was initially attributed to dry and infertile soil conditions.  When the decline eventually spread to all vineyard districts in South Africa, selectively killing only vines planted on AxR#1, it was clear that a new phylloxera host race had arisen on that rootstock (Perold, 1927; De Klerk, 1979).

Host races of phylloxera occur also with the leaf galling form of the insect.  In Canada, seven local phylloxera populations were collected from leaf galls and placed on the leaves of several Vitis cultivars.  The differential leaf galling reaction that occurred with the cultivars tested showed that at least two phylloxera biotypes existed there (Stevenson, 1970).

The occurrence of host races in France was confirmed in a laboratory root segment study using phylloxera populations obtained from the roots of the V. vinifera cultivar Alicante Bouschet and rootstock cultivars 41B and 3309 (Song and Granett, 1990).  These phylloxera populations were tested on the roots of V. vinifera cultivar Cabernet Sauvignon and the rootstocks 41B, 3309 and St. George.  The authors concluded that host races existed because differences in survivorship were found among the populations.  This result was in contrast to findings in California with phylloxera biotypes A and B, which differed in fecundity and in developmental rate, but not in survivorship (Granett, et al., 1985).  This could indicate variations in rootstock resistance mechanisms.

Evidence of phylloxera host races was discovered in a potted vine experiment conducted in New Zealand.  Phylloxera populations from Germany and New Zealand were placed onto the roots of the V. vinifera cultivar Mller-Thurgau and five rootstock cultivars.  Leaf galls, root nodosities and root tuberosities occurred with Mller-Thurgau.  Although leaf galls and root nodosities were produced on rootstock cultivar 420A, root tuberosities, which cause root death and vine decline, did not occur.  These results indicate that a host race suitable for those vines was present among the phylloxera populations used in the experiment (King and Rilling, 1985, 1991).

In Ohio, separate leaf gall populations of phylloxera from the cultivars Clinton and Concord were tested on the leaves of both cultivars.  The Clinton phylloxera colonized only the leaves of Clinton, while the Concord phylloxera colonized the leaves of both cultivars, indicating that these were separate biotypes.  Other cultivars exposed to the Clinton and Concord phylloxera populations were susceptible to only one of the biotypes.  The differences between the two phylloxera biotypes were consistent with electrophoretic tests (Williams and Shambaugh, 1987), although multiple populations of each biotype were not tested. 
In a trial conducted at Cornell University, phylloxera populations were collected from wild vines from a broad section of the eastern United States.  In laboratory root segment tests using the V. vinifera cultivar Cabernet Sauvignon, some of these insect populations could not survive.  Those that did survive were also tested with AxR#1 root segments.  Some of these populations were more successful on the roots of AxR#1 than on the roots of Cabernet Sauvignon.  The researchers concluded that biotypes in eastern phylloxera populations differ from phylloxera found in California.  Additional root segment tests and potted plant trials comparing twelve New York phylloxera populations with California phylloxera biotype A confirmed that different biotypes existed in the two states (Fergusson-Kolmes and Dennehy, 1991, 1993).   

The existence of phylloxera host races adapted to specific rootstock cultivars was demonstrated in an experiment that used phylloxera from the roots of wild and cultivated grapevines.  Life tables were developed for wild grapevine phylloxera populations by culturing the insects on AxR#1 and Cabernet Sauvignon roots.  Overall performance by these phylloxera populations on AxR#1 was equal to or greater than their performance on Cabernet Sauvignon roots.  When these phylloxera populations were cultured on the roots of AxR#1 and Cabernet Sauvignon, the phylloxera from commercial vineyards showed greater overall performance on Cabernet Sauvignon than the phylloxera from wild grapevines.  Phylloxera from commercial vineyards had greater performance on Cabernet Sauvignon than on AxR#1.  There was no difference between the performance of the phylloxera from the wild vines and the commercial vineyards on AxR#1.  The results of these trials indicated that there is genetic variation among phylloxera populations and that phylloxera in commercial vineyards has adapted to the particular cultivars used by growers (Hawthorne and Via, 1994).

In California, only the root form of phylloxera occurs.  A 1964 University of California test for the presence of phylloxera biotypes was conducted using V. vinifera x V. (Muscadinia) rotundifolia hybrids.  Phylloxera was collected from five sites in the state and grown on the roots of these vines to determine if phylloxera biotypes existed.  No evidence of different California biotypes was found in this experiment (Davidus and Olmo, 1964).  

More recently, a series of experiments has demonstrated that at least two phylloxera biotypes are present in California vineyards.  These biotypes have been designated phylloxera biotypes A and B, and are identified by their differential ability to colonize the AxR#1 rootstock.  Research now in progress on phylloxera populations collected from the roots of other rootstock cultivars indicates that many more host races exist in the state and that biotypes A and B actually each consist of a number of genetically distinct strains (Granett, personal communication, 1994).  

In the first experimental report on phylloxera biotype B in California, the decline of vines grafted on the AxR#1 rootstock caused by a phylloxera infestation in a Rutherford, Napa Valley vineyard was investigated.  Laboratory root segment studies using V. vinifera cultivar Cabernet Sauvignon and the rootstocks AxR#1 and St. George indicated differences in developmental rate and fecundity between the two biotypes.  In the laboratory, Cabernet Sauvignon was a suitable host for both phylloxera biotypes.  The AxR#1 rootstock was a suitable host only for biotype B.  The St. George rootstock did not support either biotype (Granett, et al., 1985).  Field trials to determine rootstock resistance were started in 1984 at the Rutherford vineyard.  Further root segment tests confirmed the host suitability of AxR#1 for biotype B (Granett, et al., 1987). 

Laboratory tests demonstrated that two AxR#1 selections (AxR#1-01A and AxR#1-05) were both suitable hosts for biotype B.  A field survey of biotype distribution conducted in fifteen counties in the state found only biotype A and biotype B.  However, this result occurred because only own-rooted V. vinifera and vineyards grafted on AxR#1 were included in the study, and therefore only host races relative to the AxR#1 rootstock were collected. (Granett, et al., 1991). 

In a more extensive survey of California vineyards, 118 phylloxera colonies were collected from vineyards grafted to the AxR#1 rootstock.  When these phylloxera populations were reared on AxR#1 root segments in the laboratory, again only phylloxera biotypes A and B were detected.  From bioassays the authors concluded that for California phylloxera there is a common ancestral type, and that biotype B resulted from a mutation in biotype A (De Benedictis and Granett, 1991).

The rootstock cultivar AxR#1 was developed by the French grape breeder Victor Ganzin in 1879 from a cross between the V. vinifera cultivar Aramon noir and the V. rupestris selection Rupestris Ganzin (Pongrcz, 1983).  Ganzin believed that all of his Aramon-V. rupestris hybrids had complete immunity to phylloxera (Millardet, 1892).  Viala and Ravaz (1903) found that tolerance was the actual resistance mechanism of these hybrids in France.
One of the first reported failures of this rootstock occurred in 1909 in Sicily, where it was killed by phylloxera.  Researchers there concluded that AxR#1 lacked phylloxera resistance in that region (Richter, 1909; Rossi, 1954).

A major failure of AxR#1 occurred in South Africa during the period of 1900 to 1925.  The damage was initially ascribed to a lack of phylloxera resistance on poor soils (Cillie, et al., 1920) or overcropping (Bioletti, 1908).  However, large phylloxera populations were noted on the roots of AxR#1 even in very fertile soils.  The failure was then attributed to a new phylloxera host race in South Africa (Perold, 1927).  At this time V. vinifera-American Vitis rootstocks were disappearing from other viticultural regions and the recommendation of AxR#1 in South Africa was withdrawn (van Niekerk and Theron, 1927).  The use of AxR#1 continued only in California, Australia and New Zealand (Pongrcz, 1983).

The first failure of the AxR#1 rootstock in California was detected in 1983 near Rutherford in the Napa Valley and at a few other sites.  Testing showed that biotype B phylloxera was present at these sites (Wolpert, 1988).  The spread of biotype B to other AxR#1 vineyards has been rapid.  By 1993, over 16,000 acres in the north coast districts had become infested (Weber, 1994).    

The effect of soil type on phylloxera infestation was noted soon after the insect appeared in Europe.  By 1874, it was discovered that vines growing in sandy soils low in clay in southern France were not affected by the insect, even though the surrounding region was generally infested (Bleasdale, 1880).  It is believed that in soils with a high clay content, small passages are created when the soil dries and shrinks.  This permits the insect to move along vine roots and to migrate through the soil.  Soils with a sand content over sixty percent do not support phylloxera populations in the field. (Nougaret and Lapham, 1928; Smith and Stafford, 1955).

Soil conditions also directly affect the growth of the vine.  Rootstock performance as related to soil depth, fertility and moisture content has been widely documented (Fox, 1902; Viala and Ravaz, 1903; Bioletti, 1906, 1908; Bioletti, et al., 1921; Nougaret and Lapham, 1928; Galet, 1979; Pongrcz, 1983).  Many reports have indicated that rootstocks with relatively low phylloxera resistance perform well on very deep, moist, fertile soils.  Under conditions of favorable soil type where these observations were made, apparently the vines produce enough root growth to mitigate phylloxera damage (Twight, 1903; Bioletti, 1908; Bioletti, et al., 1921). 

The role of water in the management of phylloxera and phylloxera damage may be separated into two general effects.  The first is a direct effect on the insect by the exclusion of air from the soil.  The second is the indirect effect on phylloxera by the role water plays in vine stress and growth.

Vineyard submersion during the dormant season was used successfully in the nineteenth century to control phylloxera.  However, this method is not widely applicable because it can only be used in level vineyards planted on dense soils where large amounts of water are available.  A long period of submersion is required because phylloxera is well adapted to wet soil conditions (Bleasdale, 1888; Mayet, 1894; Hayne, 1897; Fox, 1902).    
The use of irrigation to relieve water stress and enhance vine growth is a widely practiced viticultural technique.  The effect of optimum water availability on vine growth, crop yield and wine quality has been extensively studied (Neja, et al., 1977; Freeman, et al., 1979; Freeman and Kliewer, 1983; Kliewer, et al., 1983; Matthews and Anderson, 1987; Matthews, et al., 1987; Grimes and Williams, 1990). 

Summer irrigation to reduce phylloxera damage was used successfully in some early French studies (Herrison, 1888).  However, failures of summer irrigation were also reported.  In 1869, Faucon found submersion useful but felt that summer irrigation was ineffective.  In 1878, Cornu and Mouillefert found summer irrigation had no beneficial effect (Mayet, 1894). 

In the San Joaquin Valley region of California, Twight reported that V. vinifera-American Vitis rootstocks with a relatively low phylloxera rating performed well in moist, rich soils because the vine could grow additional rootlets to replace those damaged by the insect (Twight, 1903).  Bioletti reported similar success in the San Joaquin Valley, where he felt resistant rootstocks were not needed in fertile phylloxerated soils that could be irrigated (Bioletti, 1920).  Referring to vine decline in the Santa Clara Valley in California, Davidson and Nougaret found that water stress limited the ability of roots to regrow, but warned against excessive irrigation that could promote rot (Davidson and Nougaret, 1921).  Jacob stated that rootstocks with low inherent phylloxera resistance could be used if irrigation could be applied (Jacob, 1938).  Winkler reiterated this concept in his viticulture textbook (Winkler, et al., 1974).

The performance of AxR#1 appears to be closely related to soil moisture content.  In general, University of California publications recommended AxR#1 only for valley sites with deep soils well-supplied with moisture.  The rootstock was never recommended for use on dry or shallow soils, in part because of its low phylloxera resistance.  Jacob stated that there had never been a case of insufficient resistance with AxR#1 on irrigated sites in the San Joaquin Valley.  He predicted that if the rootstock were to succumb to phylloxera the failure would occur on non-irrigated sites (Jacob, 1938, 1944).  Lider repeatedly mentioned that the low phylloxera resistance of AxR#1 is mitigated by soils with a high moisture content (Lider, 1957, 1958a, 1958b).  Winkler made a similar statement about AxR#1 in his text (Winkler, et al., 1974).  Stafford and Doutt specified that AxR#1 performs well only on irrigated soils (Stafford and Doutt, 1974).

A recent article has suggested that phylloxera infestation is a symptom of water stress rather than a direct cause of vine decline (Helm, et al., 1991).  This conclusion is in opposition to the findings reported in the vast literature on the insect.  Unfortunately, the experimental design of this trial was flawed because no control treatment was included in the potted vine study, from which the authors made their conclusion.  The lack of a control made it impossible to separate the effect of water stress from the effect of phylloxera injury.  Field study data were contradictory.    


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Introduction to Thesis for PhD-Department of Viticulture & Enology- University of California at Davis 

Dr. Stephen KrebsProgram Coordinator and Vineyard Manager
Dr. Krebs runs the viticulture and winery technology program at Napa Valley College. As part of his duties, he teaches viticulture classes and manages the student vineyard. He holds a doctorate, master of science and bachelor of science from the University of California at Davis, all focusing on viticulture. He has also served as viticulturist and manager for Sunny Slope Ranch in Glen Ellen, Matanzas Creek Winery in Santa Rosa, and Mayacamas Vineyards in Napa. Stephen performed field research on grape varieties in Europe and California for author Jancis Robinson’s book Vines, Grapes and Wine.

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