Amer J of Res (1999) 76:191-197 191

Distribution of Tobacco Rattle Wlrus in Tubers of Resistant and Susceptible Potatoes and Systemic Movement of into Daughter Plants

James M. Crosslin, Peter E. Thomas*, and Charles R. Brown

USDA-ARS, 24106 N. Bunn Rd., Prosser, WA 99350. *Corresponding author. Peter E. Thomas; ph. (509) 786-9249; fax (509) 786-9277; email: [email protected].

ABSTRACT Ploeg eta/., 1992). In potato (Solanum tuberosum L.), TRV incites a disease called spralng or corky ringspot (CRS), char- Fifty-nine potato cultivars or breeding clones were acterized by internal discoloration which may form arcs or planted near Umatilla, OR and/or Pasco, WA, in fields circles. The affected tissue may have a corky texture and known to be infested with tobacco rattle virus (TRV) symptoms may be visible on the tuber surface (Harrison and and vector , Paratrichodorus allius Jen. Robinson, 1986). The virus may be present in asymptomatic (Sid.). Tubers from these field plots were cut and tissues of CRS-affected tubers of at least one cultivar (Cross- examined for corky ringspot (CRS) symptoms. Reverse lin and Thomas, 1995). transcription-polymerase chain reaction (RT-PCR) for Potatoes grown from TRV-infected tubers may become TRV was conducted on tissue samples from sympto- systemically infected and occasionally produce "stem mot- matic and asymptomatic tubers. Sixty-five percent of tle" symptoms where one or a few stems exhibit varying the symptomatic and 42% of the asymptomatic tissue degrees of mottling and discoloration. Systemic movement samples from CRS symptomatic tubers contained of TRV, however, occurs infrequently (Oswald and Bowman, detectable TRV. Approximately 2% of plants grown 1958; Harrison and Robinson, 1982; Harrison and Robinson, from either symptomatic or asymptomatic tubers con- 1986) and may relate to the level of CRS resistance of a par- tained TRV when tested by ELISA, whereas 20% and ticular cultivar (Harrison and Cooper, 1974). 12% of plants grown from symptomatic and asympto- The research described herein was conducted in order matic tubers, respectively, were positive for TRY by to (1) investigate the distribution of TRV in tissue of CRS RT-PCR. These results suggest that RT-PCR is a more symptomatic and asymptomatic tubers of numerous culti- sensitive assay for detection of TRY. Systemic infec- vars and breeding clones, and (2) determine the frequency tions by TRV were detected more often in foliage of of TRV movement from seed pieces into daughter plants. CRS-susceptible genotypes. Daughter tubers exhibit- ing symptoms of CRS, and which contained RT-PCR- MATERIALS AND METHODS detectable TRV, were produced on plants of three genotypes, including one from an asymptomatic parent CRS Evaluation tuber. in 1996, tubers of 28 potato cultivars or breeding clones were planted near Umatilla, OR in an area where CRS had INTRODUCTION been previously observed. Similarly, 31 cultivars or breeding clones were planted both at the UmatiUa site and another site Tobacco rattle virus (TRV) is a bipartite rod-shaped near Pasco, WA where a high incidence of CRS had been virus with a positive sense RNA genome and is transmitted in observed (unpublished data). The materials and sites which a persistent manner by several species of Paratrichodorus were planted are shown in Table 1. Six rephcates of 10 plants and T~chodorus nematodes (Harrison and Robinson, 1986; were planted in randomized blocks. Twenty tubers of each replicate were harvested and 10 tubers were quartered and evaluated for CRS symptoms. The mean percentage of tubers showing CRS symptoms was used as an indicator of CRS Accepted for publication December 14, 1998. resistance. The remainder of the tubers were kept in storage ADDITIONAL KEY WORDS: RT-PCR, ELISA, virus detection, Solanum and used in additional experiments described below. De- tuberosum. 192 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 76

TABLE 1.--Potato c~dtivars or brveding dones grown in two Seed Pieces Grown for Individual Genotype Site a tested by PCRb Tuberization~ Plant PCRd anky ringspot-aff~ed fields in 1996 and subsequent TX1385.12RU U U evaluation of the tube~ and daughter plants for TXAV657.27 U U tobaoco rattle virus. TXNSll2 U Seed Pieces Grown for Individual TXNS278 U U Genotype Site a tested by PCRb Tuberization~ Plant PCR ~ White Rose U,P U,P Yukon Gold U A082706.2R U -~ Russet Burbank~ Control yes yes yes A085165.1 U U U A087119.3 U U U U asix replications of 10 plants each per genotype were planted at the indi- A77715.6 U,P U,P cated sites. U: Umatilla, OR; P: Pasco, WA. Tubers were cut and examined A81480.6 U for corky ringspot symptoms. A8259.3 U,P bTubers produced at the indicated site(s) were tested by RT-PCR for TRV. A8259.5 U,P U,P P P c5-6 plants were placed into growth chambers with 12 hr photoperiod for A8292.5 U,P tuberization. A8390.3 U,P U,P P P dLeaves from individual plants within the set of 10 greenhouse grown A84118.3 U plants were tested for TRV by RT-PCR. A86102.6 U eNot tested. A87109.10 U fCertified Russet Burbank tubers which served as negative controls. A8787.2 U,P P P A8792.1 U A8793.6 U,P U,P A88345.2 U tailed procedures and results of the CRS evaluations will be A88356.1 U published elsewhere. A8836.5 U A88431.1 U A8894.8 U Reverse Transcription-Polymerase Chain A89875.5 U,P U,P U U Reaction (RT-PCR) of Tuber Tissue Abnaki U,P AC87313.3 U Tubers from 35 of the field plots (Table 1) were cut and Achirana U,P examined for CRS symptoms. Two core samples of approx- Atlantic U,P U U imately 7 mm diameter by 6 mm were excised from the ATX84706.2 U,U U AWN85510-2 U,P U,P tubers, combined, placed into microcentrifuge tubes, and BCO894.2 U stored at -20 C. Tissue samples consisted of one or more of Belrus U,P the following: CRS symptomatic tissue from symptomatic Bintje U,P U,P Bzura U,P tubers, asymptomatic tissue from symptomatic tubers and Chipeta U,P P P asymptomatic tissue from asymptomatic tubers. Tissue from Cisa U,P U,P disease-free certified seed pieces of Russet Burbank served CO85026.4 U U as negative controls and tobacco (cv. Samsun NN) tissue sys- CO86142.3 U CO86218.2 U temically infected with TRV served as positive controls. CO87106.5 U Tissues were thawed and ground with a mortar and pes- Dark Red Norland U,P fie. Total nucleic acids were isolated using the procedures of Elba U,P Kennebec U,P U,P U U Presting et al. (1995), resnspended in 500 ~ of sterile distilled Lemhi U,P P P water, and stored at -20 C. A total of 220 tuber samples were N42-11 U processed. RT-PCR for TRV was performed as previously Nemarus U,P Norkotah Russet U,P U,P described (Crosslin and Thomas, 1995). Ten microliters of NZA8904-2 U,P U,P the RT-PCR reaction were resolved on a 1.5% agarose gel Ontario U,P containing ethidium bromide. Samples were considered pos- Pirola U,P itive if a band of the predicted size (463 base pairs) was visi- Pungo U,P Ranger Russet U,P P P P ble when the gel was observed under UV light. Red La Soda U U U Russet Burbank U,P U,P U,P U,P Systemic Movement of TRVfrom Seed Pieces Sangre U Serrana U,P U,P Tubers from 90 of the Umatilla and Pasco field plots 1999 CROSSLIN, eta/.: TOBACCO RATILE VIRUS 193 were cut and examined for CRS symptoms in March 1997. susceptible to CRS included Norkotah Russet, Ranger Rus- Tuber pieces containing a single eye were planted into com- set, Kennebec, Dark Red Norland, and Lemhi. Together with mercial potting mix (Sunshine #1, Sun Gro Horticulture, Inc., Russet BLlrbank these include the most economically impor- Bellevue, WA) in a greenhouse with a 16 hr photoperiod and tant cultivars grown in the Pacific northwest. Most cultivars temperatures of approximately 22-30 C. Ideally, six samples or breeding clones which were grown at both locations had from CRS-symptomatic and four CRS-asymptomatic tubers a higher disease incidence at the Pasco site. For discussion were planted. For some cultivars or clones, however, six purposes, resistant, intermediate, and susceptible lines were symptomatic tubers were not found and symptomless tubers defmed as exhibiting 10% or less, 10.1-19.9%, and 20.0% or were substituted as necessary. The same tubers sampled for greater incidence of CRS, respectively, in either or both of RT-PCR were included in the planting. A total of 294 and 150 the 1996 Umatilla and Pasco plots. The specific data on the symptomatic and 296 and 160 asymptomatic tubers were CRS evaluation of these cultivars and breeding clones will planted from UmatiUa and Pasco, respectively. be published elsewhere. Approximately 2 weeks after emergence, individual leaves were removed and assayed by indirect enzyme-linked RT-PCR of Tuber Tissue immunosorbent assay (ELISA). (Converse and Martin, 1990) Tobacco rattle virus was detected by RT-PCR in 65 % for TRV using antiserum PVAS 820 from the American Type (46/71) of the CRS-symptomatic tissue samples excised from Culture Collection as detecting antibody. Tests were consid- tubers of 18 of the 20 genotypes tested (Table 2). Forty-two ered positive if the absorbance at 405 nm was greater than percent (35/83) of the asymptomatic tissue samples from two times that of healthy potato foliage. Approximately 4 symptomatic tubers were positive for TRV with samples weeks after the fwst test, leaves and a small amount of root from 15 of the 21 genotypes testing positive. Ten percent tissue were likewise assayed by ELISA for TRV. (6/59) of the tissue samples from asymptomatic tubers con- Leaf tissue was also assayed for TRV by RT-PCR. Single talned detectable TRV with samples from four of the 20 lines leaf disks approximately 1 cm in diameter were removed testing positive (Table 2). Negative RT-PCR results were from each of the 10 plants in the 90 greenhouse plantings obtained from all tissue samples of Serrana and approximately 4 weeks after emergence, combined, and TX1385.12RU. The symptomatic Serrana tubers exhibited tested for TRV as a "bulk" RT-PCR sample as described typical CRS symptoms, however tuber symptoms of above. After testing of the bulk samples, the 10 individual TX1385.12RU at planting were atypical of the disease. plants from 12 of the greenhouse plantings were assayed for All 17 samples of symptomatic tuber tissue from five TRV by RT-PCR (Table 1). susceptible cultivars contained detectable TRV compared with about half (23/44) of similar samples from tubers of Presence of TRV in Daughter Tubers resistant genotypes. Similarly, TRV was detected more often Approximately 8 weeks after emergence, 5-6 plants from in asymptomatic tissue from symptomatic tubers of suscep- each of 14 greenhouse plantings (Table 1) were transplanted tible as compared to resistant genotypes. into 4 L containers and placed into growth chambers with a Systemic Movement of TRVfrom Seed Pieces 12 hour photoperiod to allow tuberization. Three to four months later, tubers were harvested, cut, and examined for Although a few plants developed mild mottling resem- CRS symptoms. Tissue samples from 17 tubers were tested bling "stem mottle" disease (Cadman, 1959; Richardson, for TRV by RT-PCR as described above. 1970), there was no apparent relationship between these symptoms and the symptomatology of the parent seed piece. Potato X and Y were detected by ELISA in some RESULTS plants and may have led to development of these foliar symp- CRS Evaluation toms (data not shown). The incidence of CRS for genotypes grown at the In the fLrst ELISA test, TRV was detected in 1.5% (6/400) Umatilla site ranged from 1.7-75%, with cultivar Ontario and 0.9°/5 (4/426) of leaf samples from plants grown from CRS showing the highest incidence of disease. Genotypes grown symptomatic and asymptomatic tubers, respectively (Table at the Pasco site produced CRS incidences of 0-80%, with 3). In the second ELISA test, 1.5% (6/403) and 2.2% (9/403) of Russet Burbank the most affected cultivar. Other cultivars the leaf and root samples, respectively, grown from sympto- 194 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 76

TABLE 2.--Detection of tobacco rattle virus by reverse tran- TABLE 3.---Detection of tobacco rattle virus by ELISA in scription-polymerase chain reaction (RT-PCR) potato foliage and roots grown from corky in tissue from corky ringspot symptomatic or ringspot symptomatic or asymptomatic tubers.a asymptomatic tubers, a Second Test Sample Typeb First Test: Leaves From Sym. From Asym. Tuber (+) Tuber (+) Tuber (-) CRS Tubers Tubers Genotype Tissue (+) Tissue (-) Tissue (-) Resistancec Line Location b From From Leaves Roots I.~aves Roots Sym. Asym.c A087119.3 2/2 1/1 2/2 R A77715.6 1/2 1/2 0/4 R A8259.5 P 1/5 0/5 1/5 1/5 0/5 0/5 A8259.5 2/2 2/2 0/4 R A8390.3 P 1/6 0/4 1/6 1/6 0/4 0/4 A8793.6 1/4 0/4 0/4 R A878Z2 P 1/6 3/4 1/6 1/6 1/3 1/3 A89875.5 2/5 1/2 0/4 R A8787.2 U 0/6 0/4 0/6 1/6 0/4 0/4 ATX84706.2 3/4 1/2 0/2 R Chipeta P 1/6 1/4 1/6 1/6 1/4 1/4 Bintje 2/5 2/4 0/4 R Elba P 0/2 0/3 1/6 1/6 0/4 0/4 Cisa 3/5 0/5 0/4 R Kennebec U 0/6 0/4 0/6 1/6 0/4 0/4 CO85026.4 1/2 2/2 2/2 R Sangre U 1/1 no plants 0/2 1/2 0/3 0/3 NZA8904.2 1/5 0/1 0/4 R Ranger Russet P 1/5 0/3 1/5 1/5 0/3 0/3 TX1385.12RU 0/2 0/2 0/2 R Total Tests U,P 6/400 4/426 6/403 9/403 2/424 2/424 TXAV657.27 2/2 1/2 1/2 R (1.5%) (0.0%) (1.5%) (2.2%) (0.5%) (0.5%) TXNS278 3/4 1/3 0/2 R Resistant Total 23/44 (52%) 12/32(38%) 5/40(13%) aThis table shows only the data from cultivars or breeding clones which Chi-square" 0.076 0.609 0.598 produced at least one ELISA positive sample in either of the two tests. The remaining plants of other cultivars or breeding clones were negative A8390.3 6/6 0/5 0/4 I in both ELISA tests. The data are number of ELISA positive samples/total AWN85510.2 nt" 2/7 0/1 I number of samples tested. A total of 444 symptomatic and 456 asympto- Serrana 0/4 0/5 0/2 I matic tubers had been planted. The total number of plants tested is less Intermediate Total 6/10 (60%) 2/17(12%) 0/7 (0%) due to nonemergence of some seed pieces. Number of tests conducted Chi-square 0.740 0.012 0.378 varies between tests due to death of a few plants or delayed emergence. bLocation where the tubers used for the growout tests were produced. Kennebec 3/3 5/8 0/2 S U: Umatilla, OR; P: Pasco, WA. Norkotah Russet 2/2 4/8 0/2 S Cplants grown from corky ringspot symptomatic or asymptomatic Ranger Russet 1/1 1/4 nt S tubers, respectively. Russet Burbank 8/8 9/10 1/4 S White Rose 3/3 2/4 0/4 S Susceptible Total 17/17(100%) 21/34 (62%) 1/12 (8%) exception of A8259.5, all genotypes which produced plants Chi-squa~ 0.000 0.020 0.847 testing positive by ELISA were susceptible to CRS. In contrast to the ELISA data, however, TRV was Totalofall 46/71(65%) 35/83(42%) 6/59(10%) genotypes detected by RT-PCR in 23% (21/90) of the bulk leaf samples RB Controlf -- -- 0/5 (Table 4). In individual plant tests, 20% (13/64) and 12°/5(6/51) of leaf samples grown from symptomatic and asymptomatic aData for each genotype include tissue samples from tubers produced at the Unmt2Ua and/or Pasco sites. Data are number of samples RT-PCR tubers, respectively, were positive for TRV. No more than ~ ositive for TRV/total number of samples tested. two plants grown from a maximum of six symptomatic (+) = corky ringspot symptomatic; (-) = corky ringspot asymptomatic. tubers of any cultivar or breeding clone were positive for CResistance categories are based on symptoms of corky ringspot (CRS) observed in Pasco and/or Umatilla plots in 1996. Resistant: 10% or less; TRV in the individual plant tests. Three of the six positive Intermediate: 10.1-19.9%; and Susceptible: 20% or seater incidence of CRS. samples from asymptomatic tubers were from A8787.2 and dsignificance probability level for comparison of different CRS resis- one each from A087119.3, Lemhi, and Ranger Russet. These tance categories for each tissue type. enot tested. data indicated that TRV moved systemically more frequently fDisease-free certified Russet Burbank seed. than had been assumed from the ELISA results.

matic tubers, contained detectable TRV. Two plants grown Evaluation of Daughter Tubers from asymptomatic tubers were ELISA positive. Approximately 30% of plants grown from either CRS These ELISA data suggested that TRV rarely moved symptomatic or asymptomatic tubers failed to produce tubers. from a seed piece into potato foliage or roots. With the Tubers produced on the remaining 51 plants were cut and 1999 CROSSLIN, eta/.: TOBACCO RATILE VIRUS 195

TABLE 4.--Detection of tobacco rattle virus in leaves of grown from a CRS asymptomatic tuber, whereas the Ranger plants groum from corky ringspot symptomatic Russet and Russet Burbank were grown from CRS sympto- or asymptomatic tubers by reverse transcription- matic seed pieces. It should be noted that the Russet Burbank polymerase chain reaction (RT-PCR)2 plant which produced the symptomatic daughter tuber had previously tested negative for TRV by ELISA and RT-PCR. RT-PCR of Individual Plant Number. Bulk These results may have been due to the uneven distribution of Genotype(Umat.)b 1 2 3 4 5 6 7 8 9 10 PCR TRV in tubers (Crosslin and Thomas, 1995) and foliage. A082706.2R t nt nt nt + The RT-PCR data indicate that TRV can move systemi- A085165.1 + cally into daughter tubers from symptomatic or asympto- A087119.3 + + A8292.5 t nt nt nt + matic seed pieces and incite CRS symptoms. A8787.2 t nt nt nt + A88431.1 t nt nt nt + DISCUSSION A89875.5 + Atlantic + To our knowledge, this is the first detailed investigation Kennebec + Red La Soda + into the distribution of TRV in tubers exhibiting symptoms Sangre t nt n nt +

RT-PCR of Individuh] ~lant Number. Bulk TABLE 5.--Development of corky ringspot symptoms and Genotype(Pasco)d 1 2 3 4 5 6 7 8 9 10 PCR ~" ~ " detection of tobacco rattle virus in daughter A8259.3 nt nt nt nt + tubers produced on plants grown from corky A8259.5 .... + ringspot symptomatic or asymptomatic tubers." A8292.5 nt nt nt nt + t A8390.3 .... + A8787.2 + + + + Genotype CRS Leaf Daughter Daughter Daughter ,~ symptoms in PCRc tuber number tuber tuber A89875.5 nt nt nt nt + parent tuberb and sized symptoms° PCRf Bzura nt nt nt nt + Chipeta nt nt nt nt + Lemhi + + A087119.3 + 1 m dark stem end Ranger Russet + nt + A89875.5 + 2 s dark center Russet Burbank .... A89875.5 + + i s Atlantic + 2 m, 2 s aThis table shows results for cultivars or breeding clones which were Atlantic + 1 s, 1 m m: CRS? positive for TRV in the bulk RT-PCR tests, and/or plants which were Atlantic + 1 m CRS? tested individually. The remaining 68 bulk RT-PCR samples were negative Atlantic + 1 s, 1 m s: -, m: CRS? for TRV. Shaded boxes indicate plants grown from CRS symptomatic Kennebec + + I m tubers. Non-shaded boxes indicate plants grown from asymptomatic Kennebec 2 vs, 2 s tubers. (+) and (-) indicate RT-PCR positive and negative results, respec- A8390.3 + 2 vs, 2 m tively. Bulk RT-PCR tests consisted of one leaf disk per plant per geno- A8787.2 + + 2 vs, 1 s CRS? type processed together. Individual plant tests consisted of two leaf disks A8787.2 + 1 vs CRS + per plant. Ranger + + 2 vs CRS + bparent tubers grown at Umatilla, OR Ranger + 1 vs tiny fleck CNot tested or plants did not emerge Russet Burbank + 1 vs CRS + dparent tubers grown at Pasco, WA Russet Burbank + 1 vs, 1 s Russet Burbank - 1 vs, 2 s, 1 m small flecks RB controlg 4 s, 1 m evaluated for CRS symptoms. Discoloration resembling CRS aThis table shows the data from daughter tubers which were tested for was observed in tubers of Atlantic, A8787.2, Ranger Russet, TRV by RT-PCR. Daughter tubers produced on the other 34 plants were and Russet Burbank (Table 5). Internal discoloration not typ- asymptomatic and were not tested for the presence of TRV. ical of CRS was observed in tubers of A087119.3 and A89875.5. bpresence (+) or absence (-) of corky ringspot symptoms in parent tuber. CRT-PCR results of leaf tissue of parent plant. TRV positive (+) or nega- Tissue from these affected tubers and apparently healthy tive (-). tubers of Kennebec and A8390.3 were assayed for TRV by RT- dNumber of daughter tubers and relative size of the tubers. (vs): very smal~ PCR. One symptomahc tuber each ofA8787.2, Ranger Russet, less than about 2.5 cm; (s): small, about 4 c~ (m): medium, about 7 cm. and Russet Burbank tested positive for TRV (Table 5). Other eAbsence (-) of corky ringspot symptoms. Questionable (?) CRS symp- toms, or other symptoms as noted. discolored or asymptomatic tubers were negative for the virus. fTRV positive (+) or negative (-) by RT-PCR. The A8787.2 plant which produced the symptomatic tuber was gcertifled Russet Burbank seed. 196 AMERICAN JOURNAL OF POTATO RESEARCH Vol. 76 of CRS. Our data indicate that TRV is usually present in CRS Pasco, respectively, yet plants of both cultivars were nega- symptomatic tissue and is often present in the asymptomatic tive in the bulk RT-PCR tests. Also, RT-PCR tests failed to tissue from CRS-affected tubers. This confirms earlier find- detect TRV in individual Russet Burbank plants grown from ings (Crosslin and Thomas, 1995) in which five out of six symptomatic tubers. Similarly, Harrison (1968) reported that samples of symptomatic tissue and one out of five asympto- tubers of spraing-susceptible cultivars gave rise to fewer sys- matic tissue samples from CRS-symptomatic tubers tested temically infected plants than resistant cultivars. In contrast, positive for TRV by RT-PCR. In the present study, TRV was ELISA results (Table 3) suggest a possible relationship also detected, although infrequently, in tubers which did not between systemic movement of TRV and CRS susceptibility exhibit symptoms of CRS. In tests with a limited number of since seven of the nine genotypes which produced ELISA symptomatic tubers (Cadman, 1959), viruses of the tobacco positive plants are susceptible to CRS. Also, although only rattle type could be transmitted from the symptomatic but four plants grown from asymptomatic tubers were ELISA not healthy tissue from each of four spraing-affected tubers positive for TRV in the fwst tests, the affected genotypes, of the cultivar Kerr's Pink. Chipeta and A8787.2, were susceptible to CRS. The presence of TRV in asymptomatic tissue in our tests We found that 20% (13/64) of plants grown from CRS- may suggest that environmental factors, time of inoculation symptomatic tubers were systemically infected with TRV, by viruliferous nematodes, virus titer, or other factors, may as determined by RT-PCR. Similarly, Richardson (1973) re- play a role in development of CRS. Harrison and Cooper ported that 25% (10/40) of plants grown from spraing-symp- (1974), however, were able to incite spralng symptoms by tomatic tubers (cv. Maris Piper) exhibited stem mottle rubbing young tubers of the susceptible line Pentland Dell symptoms. However, tests confirming the presence of TRV in with purified TRV, but no spraing symptoms resulted when the foliage were not reported. tubers of the resistant line Arron Pilot were similarly inocu- Based on RT-PCR of individual plants, 12% (6/51) of the lated. However, verification of the presence or absence of plants grown from asymptomatic tuber pieces produced virus in symptomatic or asymptomatic tissue of these tubers plants systemically infected with TRV. Additionally, we noted was not reported. Samson et al. (1993) reported detection of that one CRS asymptomatic tuber piece of line A8787.2 pro- TRV by ELISA in 3 of 39 samples from tubers grown in a duced an infected plant which yielded tubers with CRS symp- TRV-infested field; however the symptomatology of the tis- toms. In contrast, Richardson (1970) found that symptomless sue samples was not specified. Similarly, Gugerli (1978) plants grown from symptomatic tubers did not produce reported detection of TRV by ELISA in some tubers exhibit- tubers with secondary spralng symptoms. ing CRS symptoms, although the specific tissue tested was In recently conducted transmission tests not described. The virus was not, however, detected in (Crosslin, unpublished), nonvinfliferous P. a//ius acquired sprouts or plants grown from diseased tubers. TRV from systemically infected potato and transmitted the The inability to detect TRV in potato foliage by ELISA virus to tobacco. The systemically infected Russet Burbank, was possibly due to the presence of"non-multiplying" or NM- Norkotah Russet, and Ranger Russet used in these tests were type infections in which nucleoprotein particles are not pro- grown from CRS-symptomatic tubers produced at the Pasco duced (Cadman and Harrison , 1959; Gugerli, 1978; Harrison field site. In fight of this result and the results presented in and Robinson, 1986). In Great Britain, research has shown this paper, we feel that tubers from fields known to harbor that most plants grown from CRS-affected tubers which TRV and nematode vectors, regardless of the presence or developed stem mottle symptoms contained NM type iso- absence of CRS symptoms, may be capable of giving rise to lates (Harrison and Robinson, 1986). Although serological plants systemically infected with TRV. It is, therefore, possi- tests would not detect NM type isolates, nucleic acid-based ble that these plants may then act as a source of TRV for detection of NM type isolates has been reported (Harrison indigenous populations of nonvirulfferous P. a//ius. and Robinson, 1982; Harrison et al., 1983). A greater percentage of plants grown from CRS-affected LITERATURE CITED tubers of CRS susceptible genotypes contained detectable TRV than similar samples of CRS resistant genotypes. How- Cadman, C.H. 1959. Potato stem-mottle disease in Scotland. Eur Potato J 2:165-175. ever, there were cases where this relationship was not Cadman, C.H. and B.D. Harrison. 1959. Studies on the properties of soil- observed. For example, cultivars Ontario and Russet Bur- borne viruses of the tobacco-rattle type occurring in Scotland. bank exhibited the highest CRS incidences at Umatilia and Ann Appl Bio147:542-556. 1999 CROSSLIN, eta/.: TOBACCO RATTLE VIRUS 197

Converse, R.H. and R.R. Martin. 1990. Elisa methods for plant viruses. Harrison, B.D., D.J. Robinson, W.P. Mowat, and G.H. Duncan. 1983. Com- Pages 179-196, In: Serological Methods for Detection and Identi- parison of nucleic acid hybridisation and other tests for detecting fication of Viral and Bacterial Plant Pathogens. R. Hampton, E. tobacco rattle virus in plants and potato tubers. Ann Ball, and S. DeBoer, eds. APS Press, St. Paul, MN. Appl Biol 102:331-338. Crosslin, J.M. and P.E. Thomas. 1995. Detection of tobacco rattle virus in Oswald, J.W. and T. Bowman. 1958. Studies on a soil-borne potato virus tubers exhibiting symptoms of corky ringspot by polymerase disease in California. (Abstr.). Phytopathology 48:396. chain reaction. Am Potato J 72:605-609. Ploeg, A.T., D.J.F. Brown, and D.J. Robinson. 1992. Acquisition and sub- Gugerli, P. 1978. The detection of two potato viruses by enzyme-linked sequent transmission of tobacco rattle virus isolates by Paratri- immunosorbent assay (ELISA). Phytopath Z 92:51-56. chodorus and Trichodorus nematode species. Neth J Plant Path Harrison, B.D. 1968. Reactions of some old and new British potato cul- 98:291-300. tivars to tobacco rattle virus. Eur Potato J 11:165-176. Presting, G.G., O.P. Smith, and C.R. Brown. 1995. Resistance to potato Harrison, B.D. and J.I. Cooper. 1974. Studies on the nature of the resis- leafroU virus in potato plants transformed with the coat protein tance of potato cultivars to tobacco rattle virus. Pot Res 17:348- gene or with vector control constructs. Phytopathology 85:436- 349. 442. Harrison, B.D. and D.J. Robinson. 1982. Genome reconstitution and Richardson, D.E. 1970. The assessment of varietal reactions to spraing nucleic acid hybridization as methods of identifying particle-defi- caused by tobacco rattle virus. J Nat Inst Ag Bot 12:112-118. cient isolates of tobacco rattle virus in potato plants with stem- Richardson, D.E. 1973. An external ringspot of potatoes. P1 Path 22:120- mottle disease. J Virol Methods 5:255-266. 122. Harrison, B.D. and D.J. Robinson. 1986. Tobraviruses. Pages 339-369. In: Samson, R.G., T.C. Allen, and J.L. Whitworth. 1993. Evaluation of direct The Plant Viruses, Vol. 2: The Rod-shaped Plant Viruses. M.H.V. tissue blot~ng to detect potato viruses. Am Potato J 70:257-265. van Regenmortel and H. Fraenkel-Conrat~ eds. Plenum Press, NY.