Invited Review Grapevine Yellows in Italy: Past, Present and Future
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002_JPPReview(Belli)_303 9-07-2010 11:56 Pagina 303 Journal of Plant Pathology (2010), 92 (2), 303-326 Edizioni ETS Pisa, 2010 303 INVITED REVIEW GRAPEVINE YELLOWS IN ITALY: PAST, PRESENT AND FUTURE G. Belli1, P.A. Bianco1 and M. Conti2 1 Dipartimento di Produzione Vegetale, Sezione Patologia Vegetale, Università degli Studi, Via Celoria 2, 20133 Milano, Italy 2 Istituto di Virologia Vegetale del CNR, Strada delle Cacce 73, 10135 Torino, Italy SUMMARY for new plantations, and insecticide sprays against S. ti- tanus. Thanks to these measures, a sharp decrease of Following the discovery and description by the mid- FD incidence has been registered in the last few years in dle of the past century in France of an epidemic all affected areas of the country. Research on GY in grapevine disease called Flavescence dorèe (FD), com- Italy is now focusing mostly on epidemiological aspects parable disorders known with the general name of (e.g. new potential insect vectors), new control practices Grapevine Yellows (GY) were reported from all major such as genetic resistance to either FD or BN, or both, grape-growing countries of the world, where they con- use of thermotherapy on propagation material, and in- stitute a serious threat to viticulture. In Italy, FD and vestigation of the possible role of symbiotic micro-or- Bois noir (BN), the two most important diseases of the ganisms present in host plants and insect vectors as an- GY group, have been recorded since the 1970’s, both tagonists of the phytoplasma agents of GY. representing a major concern for grapevine growers. FD is caused by phytoplasmas of the ‘elm yellows’ or 16Sr- V taxonomic group and is transmitted by the leafhop- INTRODUCTION per Scaphoideus titanus in the persistent-propagative manner. Severe FD epidemics started about two Grapevine yellows (GY), a group of diseases that were decades ago and are still in progress in the main viticul- originally thought to be caused by viruses, are now known tural districts of northern Italy, i.e. Liguria (Italian Riv- to have a phytoplasma aetiology. The first such disorder to iera), Lombardy, Piedmont and Veneto. The disease in- be reported from Vitis vinifera, and the most widely cidence may exceed 50% and the economic losses can known of the GY group, is certainly Flavescence dorée be very high. BN is caused by phytoplasmas of the ‘Stol- (FD), which appeared in south-west France in the 1950’s, bur’ or 16S-XIIA group transmitted in the persistent- from where it spread to other viticultural districts of propagative manner by the planthopper Hyalesthes ob- France, northern Italy and neighbouring European coun- soletus. Other hopper species may also act as vectors tries. Bois noir (BN), whose symptoms are indistinguish- since the disease has been observed to spread actively in able from those of FD, was also first reported from France, geographic areas where H. obsoletus does not occur. then from the most important viticultural areas of Europe. Currently, the presence of FD seems limited to northern During the last forty years or so, other diseases re- Italy, i.e. the Po Valley and a few regions south to it, like sembling FD and BN have been observed and studied Marche, Tuscany and Umbria (central Italy). Its vector, in many countries all over the world. All these diseases however, has occasionally been found also in regions are associated with the presence of phytoplasmas, which further south. BN occurs throughout the country and are now regarded as their effective aetiological agents, its incidence, initially believed to be negligible by com- and closely resemble each other in symptomatology. In parison with that of FD, has recently attained economi- fact, affected vines show downward rolling of the leaves cally important levels in some districts. FD and BN are accompanied by yellow or bright red discoloration of symptomatologically undistinguishable from one anoth- veins and blades, berry withering and uneven or total er, molecular diagnosis is therefore necessary for the lack of cane lignification. GY, however, have different proper identification of the agent. Since 2000, compul- phytoplasma species as causal agent, as well as different sory control measures against FD are enforced in Italy insect vectors, which are either leafhoppers or plan- by a govermental decree. These consist mainly in the thoppers (Homoptera:Auchenorrhyncha) that feed ei- elimination of infected vines, the use of healthy material ther specifically or occasionally on the vines. It is worth noting that two or more different phytoplasma species may infect simultaneously individual grapevines, thus Corresponding author: G. Belli Fax: +39.02.50316781 causing mixed infections. The symptoms, however, do E-mail: [email protected] not differ from those outlined above. 002_JPPReview(Belli)_303 9-07-2010 11:56 Pagina 304 304 Grapevine yellows in Italy Journal of Plant Pathology (2010), 92 (2), 303-326 Although phytoplasmas are non culturable microor- be consequent to root damage, excluding any correla- ganisms and, in the case of GY, Koch’s postulates have tion with infectious agents. Finally, Caudwell (1957), af- not yet been fulfilled, when phytoplasmas of a specific ter two years of detailed observations and transmission group or subgroup are found consistently associated tests, determined that FD was an infectious disease, with a specific grape disease, they are regarded as being probably caused by a virus (phytoplasmas were un- its causal agents. In fact, the identification of phytoplas- known at that time and yellows diseases of different mas as the cause of GY was finalized in the last decades crops were thought to have a viral aetiology). A few when molecular detection methods became available, years later Schvester et al. (1961) provided experimental thus allowing to distinguish from one another the phy- evidence that FD was spread in the vineyards by the toplasma species involved in each single disease. leafhopper Scaphoideus titanus (originally named S. lit- The current information on GY vectors is still largely toralis), an insect accidentally introduced from North incomplete. Whereas it has long been known that FD is America some years before. Since FD was the first dis- transmitted in nature by the leafhopper Scaphoideus ti- ease of the GY group to be investigated in detail and tanus Ball and, more recently, that BN can be transmit- described, it is still universally considered as the typical ted by the planthopper Hyalesthes obsoletus Signoret, representative of the GY group. little is known on the vectors of other GY. Furthermore, Meanwhile, during the 1960’s, another different GY it seems clear that H. obsoletus may not be the only nat- disease was reported by Caudwell (1961) under the ural vector of BN, for this disease spreads actively also name of “bois noir” (BN). BN was primarily present in in areas where this planthopper does not occur, and a some vineyards of north-eastern France and was charac- few other hopper species were identified as potential terized by symptoms very similar to those of FD but, BN vectors, e.g. Pentastiridius beieri and Reptalus quin- because it was spreading more slowly, it was at first con- quecostatus (Gatineau et al., 2001; Holzinger et al., 2002; sidered a non epidemic form of FD. Ten years later, Trivellone et al., 2005). It seems, then, that the relation- Caudwell et al. (1971b) established that BN had to be ship between diseases and insect vectors is a subject that regarded as a disease distinct from FD, primarily on the needs to be more deeply investigated for a better under- basis of its non transmissibility by S. titanus. standing of GY epidemiology and for the hopeful devel- A few years earlier, similar symptoms had been ob- opment of new sustainable means for their control. served in Germany, in vineyards of the Mosel and the Damage caused by GY may in fact be extensive and Rhein Valley by Gaertel (1965), who considered them economically relevant, since most of the crop of diseased as FD expressions, albeit S. titanus did not occur in vines is lost. In the last decade of the past century, FD the affected stands. This disease was later studied in epidemics have affected the vineyards of all the northern the same area by Mendgen (1971), who called it regions of Italy causing dramatic yield losses, while BN “Vergilbungskrankheit” (VK), then by Maixner is expanding in both the northern and southern parts of (1994), who provided experimental evidence of its the country, with great concern of the growers. transmission by the planthopper Hyalesthes obsoletus. This review is intended to provide an historical view We now know that BN and VK are the same disease, of GY in Italy and to describe the present situation with i.e. the likely cause of the yellows-type symptoms de- a look at future prospects. scribed by Ravaz and Verge (1924), when S. titanus was not yet present in Europe. From the 1970’s onwards, diseases similar to FD and HISTORICAL BACKGROUND BN were recorded from countries other than France and Germany, such as Rumania (Rafaila and Costache, First reports of grapevine yellows in France and oth- 1970), Italy (Belli et al., 1973), Israel (Tanne and er countries. Symptoms resembling those of GY had Nitzany, 1973), Greece (Rumbos and Biris, 1979), Chile been observed in France since the beginning of the past (Caudwell, 1980), Australia (Magarey and Wachtel, century and described by Ravaz and Verge (1924) under 1982), USA (Pearson et al., 1985), and in many other the names of “flavescence” and “rougeau”. However, it grapevine-growing areas of the world (Martelli and was around 1950 that a new disease began to appear Boudon Padieu, 2006). and spread in the vineyards of south-west France (espe- cially in Gascogne and Armagnac, where the first epi- First reports of GY in Italy.