Research Note
Grapevine trichovirus A (GVA) and grapevine trichovirus B (GVB) were successfully transferred with bulk transmission trials under controlled conditions, from infected grapevines to herbaceous hosts by Pseudococcus affinis MASK., a pseudococcid mealybug that may attack grapevines. P. affinis is the fourth mealybug species capable of vectoring GVA and GVB, confirming that transmission by mealybugs of grapevine trichoviruses may not be species-specific

Boscia, D.

Fiori, M.

Garau, R.

Prota, U.

Prota, V. A.

English

JKI Open Journal Systems (Julius Kühn-Institut)

Vitis 34 (1), 67-68 (1995) Research Note Pseudococcus affinis MAsK., new vector of grapevine trichoviruses A and B R. GARAU, V. A. PROTA1) , D. BoscrA2), M. FroRr 1) and U. PROTA1) . S .u m~ a r y : Grapevine trichovirus A (GVA) and grape-vme tnchov1rus B (GVB) were successfully transferred with bulk transmission trials under controlled conditions, from infected grapevines to herbaceous hosts by Pseudococcus affinis MASK., a pseudococcid mealybug that may attack grapevines. P. affinis IS the fourth mealybug species capable of vectoring GVA and G.VB, ~onfirming that transmission by mealybugs of grapevine tnchov1ruses may not be species-specific. K e y w o r d s : trichoviruses, transmission, mealybugs, epidemiology. Introduction: Pseudococcus affinis MASK. is a polyphagous pseudococcid mealybug present in several areas of the world. In the southern emisphere (McLACHLAN 1970) and Western America (WrLKEY and McKENZlE 1961· GoNZALES 1983; RIPA and RoJAS 1990), it is also reported as a grapevine pest. In Sardinia (Southern Italy) P. affinis thrives primarily on the sclerophyllous shrubs of the Medi-terranean scrub and, although it apparently does not attack Vitis species in the field, it can occasionally be found colo-nizing glasshouse-grown vines. Thus, it may represent a potential virus vector, similarly to other mealybugs of the Planococcus and Pseudococcus genera (reviewed by BovEY and MARTELLI 1992; MARTELLI 1993). This paper reports the results of trials in which the vectoring ability of P. affinis was experimentally tested. Materials and methods: A P. affinis population was collected from a naturally infested myrtle plant (Myrtus communis) near Sassari and transferred to young sprouts of virus-free potatoes growing in glass jars in a climatized greenhouse at a temperature EB 25 °C. Under these condi-tion.s, the mealybugs adapted readily to the new host pro-ducmg a new generation in about 5 weeks. Mealybug populations thriving on potatoes were used for bulk transmission tests made in a growth chamber at 25 oc and 16 h photoperiod (3,500 lx) . Infected grapevine rootlings served as donor and herbaceous plants as recipi-ent hosts . Two sets of trials were carried out: T r i a l 1 : Donors were pot-grown rooted cuttings from a cv. Italia vine (accession I 9117) that had indexed 1) Istituto di Patologia Vegetale, Universita degli Studi , Via E. De Nicola, I-07100 Sassari, Italy; 2) Dipartimento di Protezione delle Piante, Universita degli Studi and Centro di Studio del CNR sui Virus e le Virosi delle Colture Mediterranee, Via Amendola 165/A, I-70126 Bari, Italy positive for corky bark and was known to be infected by a necrotic strain of grapevine trichovirus B (GVB) (GARAU et al. 1993; BoscrA et al. 1994) and ordinary isolates of grapevine trichovirus A (GVA) and grapevine leafroll-as-sociated virus 3 (GLRa V-3) . Fragments of P. affinis-in-fested potato sprouts were placed on grapevine rootlings and the mealybugs were let to multiply undisturbed for 40 d . Then, no less than 30 1st and 2nd instar crawlers were removed from grapevine leaves with the piece of tis-sue on which they were feeding and were placed on each of 5 plants of Nicotiana occidentalis, N. cavicola and Gomphrena globosa. Controls consisted of an equal number of plants of the same species that were infested with mealybugs reared on healthy potatoes. T r i a 1 2 : Donors were rootlings from a cv. Italia vine (accession I 7/8) infected by GVA, GLRaV-3, grape-vine corky bark-associated closterovirus (GCBaV) and grapevine fanleaf nepovirus (GFLV). Mealybugs were placed on donor vines and after an acquisition period of 30 d were transferred with the same technique as above to 3 plants each of N. occidentalis, N. clevelandii, and N. benthamiana Plants of the same species exposed to non viruliferous mealybugs served as controls. All herbaceous hosts were observed for symptom ex-pression and were individually checked in ELISA (CLARK and ADAMS 1977) and immunoelectron microscopy (IEM) (MrLNE and LuiSONI 1977) for virus detection and identifi-cation. Results and discussion: In both trials P. affinis thrived and multiplied very well on grapevine rootlings . It also adapted to the different herbaceous hosts, although with some difficulty. However, many of the mealybug crawlers transferred from grapevines fed and survived on these plants . In the first trial, a light vein clearing began to show on a N. occidentalis plant after 10 d from exposure to mealybugs that had fed on donor vines. In the week that followed , the symptoms became stronger and indistinguish-able from those induced by necrotic isolates of GVB fol-lowing mechanical inoculation (GARAU et al. 1993; BoscrA et al. 1994) and developed on the remaining 4 N. occiden-talis and the 5 plants of N. cavicola. On this latter host the symptomatology was the same as that induced by mechani-cally inoculated GVB isolates (GARAU et al. 1993; BoscrA et al. 1994). All symptomatic Nicotiana plants were ELISA and IEM positive for GVB but did not react with antisera to GVA and GLRaV-3. Controls were always negative. All 5 G. globosa seedlings that had been exposed to presumably viruliferous mealybugs reacted in 10-15 d with a systemic interveinal mottling of varying intensity, whilst the controls remained symptornless. Symptomatic plants were ELISA and IEM positive for GVA, but not for GVB and GLRaV-3 . The presence of GVA was further ascer-tained by immunogold labelling IEM (F. FAORO, personal communication) and through subinoculations to N. bentha-miana. None of the 3 viruses was detected in the controls. In the second trial, 2 of 3 N. benthamiana seedlings exposed to presumably viruliferous mealybugs, showed in 68 R. GARAU, V. A. PROTA, D. Bosc1A, M. FIORI and U. PROTA about 10 d symptoms indistinguishable from those induced by GVA following mechanical inoculation. The remaining seedling and those of N. occidentalis and N. clevelandii remained symptomless, similarly to the controls . Sympto-matic plants reacted positively for GVA in ELISA and IEM but were negative for the other vimses tested (GLRaV-3, GCBaV, GFLV). All asymptomatic plants and the controls were ELISA negative. The results of the present trials provide evidence that P. affinis is capable of acquiring GVA and GVB from dis-eased vines and of moving it to herbaceous hosts with bulk transmission experiments. Actually, it looked as if that this mealybug species could discriminate between GVA and GVB by picking up the 2 vimses from a mixture and trans-mitting them individually to different herbaceous hosts . This may be due either to a really differential vectoring ability of P. affinis and/or to the diverse susceptibility of the herbaceous indicators to these viruses . In fact, GVA, but not GVB, can infect G. globosa (BosclA et al. 1994; MARTELLI et al. 1994), whereas GVB seems to be more readily transmissible and aggressive than GVA to N. occi-dentalis and N. cavicola. Whatever the explanation, the point remains that P. affinisis a vector of grapevine trichovimses, thus join-ing the list of the hitherto identified mealybug vector spe-cies (BOVEY and MARTELLI 1992; MARTELLI 1993), and add-ing strength to the notion that mealybug transmission of these viruses may not be species-specific. Research supported by the National Research Council of Italy, Special Project RAISA, Subproject No. 2, Paper No. 2054. The authors wish to thank Dr. S . M AROTTA, University of Basilicata, Potenza, for the identificat ion of Pseudococcus affinis, Dr. F. FAORO, University of Milano for the help with IEM assays, Mr. M. Ru1u and G. ToLU for the technical ass istance, and Prof. G. P. MARTELLI for ctitical reading of the manuscript. BosctA, D.; Asou-GHANEM, N. ; SALDARELLI , P.; MtNA FRA, A.; CASTELLANO, M. A.; GARAU, R.; SAVINO, V.; MARTEL LI , G. P.; 1994: A comparative study of grapev ine virus B iso lates. Riv. Patol. Veget. , Ser. V, 4, 11 -24. BovEY, R.; MARTELLI , G. P.; 1992: Directory of Major Virus and Virus-like Diseases of Grapevines. Mediterranean Fruit Crop Improvement Council and International Council for the Study of Viruses and Virus Diseases of the Grapevine, Bari. CLARK, M. F.; ADAMS, A. N.; 1977: Characteristics of the micraplate method of enzyme-linked immunosorbent assay for the detection of plant viruses . J. Gen. Viral. 34, 475-483. GARAU , R. ; PROTA, V. A. ; BosctA, D.; PtREDDA, R. ; PROTA, U. ; 1993: Studies on grapevine vi rus B isolates from corky bark-affected vines in Sar-dinia . Ri v. Patol. Veget. , Ser. V, 3, 83-89. GoNZALES, R. H. ; 1983: Manejo de plagas de la vi d. Fac. Cienc. Agrar. Vet. Forest. Univ. Chili. Pub!. Cienc. Agrar. No. 10, Santiago. MARTELLI , G. P. (Ed.) 1993: Graft-transmissible Diseases of Grapevines. Handbook for Detection and Diagnosis. FAO Publication Division, Rome. - -; BOSCIA, D.; CHOUEIRI, E.; DIGIARO, M.; CASTELLANO, A. M.; SAVINO, V. ; 1994: Occurrence of filamentous viruses and rugose wood of grape-vine in Yemen. Phytopathol. Medit. 33, 146- 151. McLAC HLAN, R. A.; 1970: Grape pest control in Queensland. Queens!. Agricult. J. 96, 23 1-235. MtLNE, R. G. ; LutsONI, E.; 1977: Rapid immune electron micrascopy of virus preparations. Method. Viral. 6, 265-28 1. RIPA, S. R. ; RocHAS, P. S. ; 1990: Manejo y control biologico del chanchito blanco de la vid. Rev. Frutic . 11 , 82-87. WtLKEY, R. F. ; McKENZIE, L. L.; 1961: Systematic status of the Pseudococcus maritimus-malvacearum complex of mealybugs (Homoptera ; Coccidea: Pseudococcidae). Bull . Calif. Dept. Agricult. 50, 245-249. 

Pseudococcus affinis MASK., new vector of grapevine trichoviruses A and B

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Pseudococcus affinis MASK., new vector of grapevine trichoviruses A and B

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