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Transmission of Tomato Ringspot Virus by Xiphinema Americanum and X

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Transmission of Tomato Ringspot Virus by Xiphinema Americanum and X Journal of Nematology 20(2):304-308. 1988. © The Society of Nematologists 1988. Transmission of Tomato Ringspot Virus by Xiphinema americanum and X. rivesi from New York Apple Orchards 1 LAURA L. GEORGI 2 Abstract: Populations of Xiphinema americanum and X. rivesi were collected from apple orchards in eastern and western New York and tested in the laboratory for ability to transmit tomato ringspot virus (TmRSV) to cucumber and dandelion. Populations varied in the frequency with which they transmitted TmRSV, but this variation did not correspond to variation in disease prevalence in the orchard. The lower prevalence of TmRSV-incited disease in apple trees in western New York cannot be attributed to inability of the local Xiphinema sl0p. to transmit TmRSV. Key words: Cucumis sativus, Taraxacum ojficinale, tomato ringspot virus, Xiphinema americanum, X. rivesi. Tomato ringspot virus (TmRSV) causes MATERIALS AND METHODS a potentially lethal disease of some apple Nematode populations: One X. americanum cuhivars grafted onto certain rootstocks population from western New York (C) and (13,15). There are extensive plantings of one from the Hudson Valley (F), one X. susceptible trees throughout the apple- rivesi population from western New York growing regions of New York, but disease (E), and a mixed population (34% X. ameri- prevalence is higher in the Hudson Valley canum, 66% X. rivesi) from the Hudson Val- than in western New York (14). Because ley (G) were selected for study. Populations TmRSV is transmitted by Xiphinema ameri- F, E, and G were associated with diseased, canum and X. rivesi (2), one possible expla- TmRSV-infected apple trees, and popu- nation for the observed distribution of dis- lation C with healthy trees (Gonsalves, pers. eased trees is variation in the ability of local comm.). Soil samples containing nema- Xiphinema spp. populations to transmit the todes from these populations were collect- virus. The objectives of the present study ed in the autumn in 1983 and 1984 and were 1) to check for variation in the ability were stored at 4 C until needed. Trans- of local populations to transmit TmRSV; mission experiments were conducted using 2) to distinguish between variation in ag- infested orchard soil or nematodes extract- gressiveness of the vector populations or ed by sieving and returned to soil within 3 their associated virus and variation in the hours (1,8). level of virus infestation acquired by the Virus isolates: TmRSV isolates were ob- vectors in the orchards as the source of tained from cucumber (Cucumis sativus L. differences in the frequency of transmis- 'Marketer'), dandelion (Taraxacum offici- sion of orchard-acquired TmRSV; and 3) hale Weber), strawberry (Fragaria ×ana- to investigate the possibility of coadapta- nassa Duch. 'Catskill'), and common tion of local virus isolates and vector pop- cinquefoil (PotentiUa canadensis L.) growing ulations. in pots of soil infested with Xiphinema spp. from populations E, F, and G. An addi- tional virus isolate was obtained from dan- delion growing under declining, TmRSV- Received for publication 25 February 1987. Part of a Ph.D. dissertation submitted to Cornell Uni- infected prune trees (Gonsalves, pers. versity, Ithaca, NY 14853. 2 Division of Biological Sciences, University of Missouri, comm.) near population C. Isolates were Columbia, MO 65211. propagated in mechanically inoculated Ca- The author thanks Dr. D. Gonsalves, New York State Ag- ricultural Experiment Station, Geneva, for sharing the results tharanthus roseus (L.) G. Don. of his survey of TmRSV in New York orchards and for pro- Plants and growing conditions: Cucumber viding antisera to TmRSV. Marian Strang, Susan McCouch, Liz Loder, and Mary Gieselman provided technical assis- and dandelion seeds were obtained from tance. Stokes Seeds, Buffalo, New York. Week- 304 Transmission of TmRSV by Xiphinema spp.: Georgi 305 old cucumber seedlings in 500-ml clay pots 83-1, but an intermediate level and a low were used in all experiments, and 2-week- level were added, corresponding roughly old dandelion seedlings in 250-ml clay pots to 50 and 10 Xiphinema spp. per pot. In a were used in one experiment (La-83-2). Six third experiment with the 1983 collections noninoculated seedlings planted in pas- (Or-83-3) and in experiments with the 1984 teurized (heated to 70 C for 30 minutes collections (Or-84-1 through Or-84-3), with aerated steam) or autoclaved soil Xiphinema spp. were sieved from the soils, served as controls. All experiments were handpicked, and added 10 per pot to the conducted in growth chambers at 22 C on root zones of individual cucumber seed- photoperiods of 14 or 15 hours. Plants were lings in pasteurized soil. fertilized every 10 days with a complete Transmission of laboratory-acquired virus: (23-19-17, N-P-K) soluble fertilizer. Nema- Two kinds of experiments compared trans- todes were permitted 4 weeks transmission mission of TmRSV by Xiphinema spp. that access. acquired the virus in the laboratory. In ex- Enzyme-linkedimmunosorbent assay (ELISA): periments La-83-1 and La-83-2, nema- Presence of virus in experimental plants todes from populations E, F, and G were was determined by ELISA (3,4). Antibod- provided access to cucumbers inoculated ies prepared against TmRSV (PYBMV with the corresponding (local) TmRSV iso- strain and a grape isolate [7] of TmRSV) lates to provide the populations with sim- were provided by Dr. D. Gonsalves, New ilar exposures to virus before transmission York State Agricultural Experiment Sta- tests. Because the nematodes used in these tion, Geneva. Well-washed root samples experiments were permitted access only to were ground using a Tissuemizer (Tekmar virus isolates from the same source, they Co., Cincinnati, OH) (0.35 g tissue in 7 ml were not first freed of virus acquired in the buffer) or Polytron (Brinkman Instru- orchard. In experiments La-84-1 through ments, Westbury, NY) homogenizer (0.5 g La-84-6, virus-free nematodes from pop- tissue in 10 ml buffer). Absorbances at 405 ulations C, E, or F were provided access to nm were read on a Dynatech microelisa cucumbers inoculated with a virus isolate autoreader, dual wave-length mode (ref- from the same (local virus) or a different erence wave-length 450 nm). A sample was (alien virus) source. To obtain virus-free rated positive if its absorbance exceeded nematodes from populations E and F, the the mean plus four standard deviations of nematodes were maintained for 3 months the negative control samples. in 3-liter clay pots planted with sudangrass Transmission of orchard-acquired TmRSV: (Sorghum vulgare var. sudanense Hitchc. Populations E, F, and G were sampled in 'Piper'), a nonhost of the virus. 1983 and tested for ability to transmit or- Virus acquisition access was provided in chard-acquired TmRSV to cucumber, and 3-liter (experiments La-83-1 and La-83-2) populations E and F were sampled and or 2.5-liter (experiments La-84-1 through tested again in 1984. Population C was not La-84-6) clay pots containing the nema- viruliferous, based on assays of cucumber tode-infested orchard soils planted with 4- seedlings planted in soil infested with 6 cucumber seedlings per pot. The seed- nematodes from this population. In two lings were mechanically inoculated with an experiments with the 1983 collections (Or- isolate of TmRSV within a day of trans- 83-1 and Or-83-2), the numbers of Xiphi- planting. Each acquisition pot was placed nema spp. per pot were equalized by dilut- inside a second clay pot of the same size to ing the infested soils (v/v) with pasteurized reduce water loss without eliminating gas soil from orchard F. In experiment Or- exchange through the pot walls. In exper- 83-1, nematode inoculum was adjusted to iments La-84-1 through La-84-6, addition- about 100 Xiphinema spp. per pot. In ex- al pots of infested soil were planted with periment Or-83-2, the highest level of in- noninoculated cucumbers to confirm that oculum was the same as in experiment Or- the nematodes were initially virus-free. 306 Journal of Nematology, Volume 20, No. 2, April 1988 TABLE 1. Transmission of orchard-acquired to- and signed rank test for two-way compar- mato ringspot virus by Xiphinema spp. from New York isons and the Quade test (an extension of apple orchards to cucumber seedlings in the labora- tory. the signed rank test) for three-way com- parisons (5). In the event of a significant Vectors Infected plants (plants tested)'t" Quade test, multiple comparisons were used Experi- per to determine which of the three entities ment plant Pop. E Pop. F Pop. G were significantly different. Or-83-1:~ 100 6 (10) 3 (10) 9 (10) Or-83-2~k 100 6 (9) 9 (9) 9 (9) RESULTS 50 7 (9) 6 (9) 9 (9) 10 3 (9) 2 (9) 7 (9) Transmission of orchard-acquired TmRSV: Or-83-3§ 10 3 (14) 2 (14) 6 (14) Among the 1983 collections, orchard-ac- Or-84-1 § 10 14 (30) 5 (30) Or-84-2§ 10 23 (30) 12 (30) quired TmRSV was transmitted to cu- Or-84-3§ 10 5 (10) 1 (10) cumber most frequently by the mixed- Population E is X. rivesi from western New York, F is X. species population G, followed by the americanum from the Hudson Valley, and G is a mixture of single-species populations E and F, usually 34% X. americanum and 66% X. rivesi from the Hudson Valley. "[" Based on ELISAs of root tissue. in that order (Table 1). The Quade test on :~ Numbers of nematodes per plant were equalized by di- the combined 1983 results was significant luting infested soils with pasteurized soil from orchard F (numbers approximate).
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