Introduction
Beet western yellows virus (BWYV), an aphid-vectored luteovirus, causes a pronounced, bright yellow color to the leaf margin of lettuce, spinach, and other leafy greens. Interveinal chlorosis may also develop. The virus does not usually stunt growth and is not considered a problem in many susceptible crops. However, where the leaves are harvested or comprise the edible portion of the crop, such as with lettuce, spinach, Chinese cabbage, and root crops sold with the shoots attached, even a slight expression of symptoms can render the crop unmarketable.
This problem has increased dramatically in recent years, perhaps influenced by changing weather patterns that favor increased numbers of aphid vectors. Another factor is the prevalence of both weedy and cultivated host species. This makes control extremely difficult as even a grower who practices perfect phytosanitary practices cannot control the practices of neighbors, particularly in the mixed woodland-row crop-pasture land use patterns typical of the Willamette Valley.
The winged aphids that spread the disease are difficult to control with insecticides. New flights entering an area must be constantly monitored and eradicated immediately. Thus, the best solution may be to find varieties or breeding lines that are resistant to the disease or that do not strongly express the symptoms. Tolerant varieties of crisphead lettuce have been developed for the Salinas Valley of California and resistance has been found in some European lines, so the appropriate germplasm may be available to breeding programs. The purpose of this trial was to screen a wide number of spinach and lettuce varieties for tolerance to BWYV.
Methods
In 1991, seed companies known to produce lettuce and spinach were contacted for trial samples. In late April the NWREC plot area was treated with a broadcast, incorporated application of 1000 pounds/acre of 10N-8.7P-16.7K fertilizer. A mixture of Rainier spinach and Detroit Dark Red table beet seed was broadcast over the plot area and over a 50-foot wide buffer area around the plots in the variety trial. The spinach, beets, and weedy species were allowed to grow uncontrolled in this area as a potential reservoir for the virus and as a shelter for the aphid vectors.
On 17 June, 53 lettuce and 24 spinach varieties were seeded into a rototilled section in the middle of the plot area. Each variety was seeded twice in 10-foot long plots. Pronamide was applied to the lettuce area at 1.5 pounds per acre for weed control. No herbicide was used on the spinach. An additional 150 pounds ammonium nitrate/acre was applied three weeks after seeding. On 27 June, 58 lettuce and 25 spinach varieties were seeded on a bed in a commercial lettuce field near Aurora, Oregon. The bed was located at the edge of the field next to a weedy fence-row and pasture. Plot length was 15 feet with one replication. The plots were sidedressed twice with ammonium nitrate, with a total N application of 100 pounds/acre. One replication of the same varieties was also planted at the OSU Vegetable Crops Research Farm on 24 June. Fertilizer consisted of 12N-12.6P-8.3K-4S at 450 pounds/acre, banded at planting. No herbicide was used. Twenty-one varieties of spinach were seeded adjacent to the earlier trial at NWREC on 15 August. Plot length was 15 feet with two replications. The earlier trial, now heavily infected with BWYV, was left as a source of virus inoculum. In all trials, lettuce was thinned to 10-12 inches between plants. Spinach was not thinned. No insecticides were used at any site. Plots were sprinkler-irrigated as necessary.
Observations of virus symptoms and other quality characteristics were made periodically. The scores reported in the tables are for the final observation of each planting (5-7 August for the NWREC and grower plots for both lettuce and the early spinach planting, 19 August for the OSU Vegetable Crops Farm planting, and 26 September for the second spinach planting at NWREC). Data presented are averaged over all sites and replications. Quality characteristics were rated on a five-point scale with 1 equal to least intense and 5 equal to most intense. Thus, a low score is desirable for virus symptoms and tendency to bolt, while a high score is desirable for color and overall score. In addition to an intensity of symptoms score, the percentage of symptomatic plants was determined for the lettuce varieties. For all plantings, presence of the virus in symptomatic plants was confirmed by enzyme-linked immunosorbant assay.
The seed used in the 1992 trial was drawn primarily from material donated in 1991. Promising varieties were included along with several known to be highly sensitive to BWYV. Methods were similar except as follows. On 16 June, 34 lettuce and 18 spinach varieties were seeded in the middle of the plot area. Each variety was seeded four times in 10-foot long plots. Fifty pounds N/acre was applied as ammonium nitrate immediately after seeding and another 100 pounds N/acre were applied three weeks after seeding. Observations of virus symptoms and other quality characteristics were made on 27 August.
Results and Discussion
1991
Lettuce varieties differed greatly in expression of BWYV virus symptoms (Table 1). Many of the varieties with a low score for BWYV intensity were red-pigmented leaf or Romaine types and slow-growing. Late maturity is related to delayed BWYV expression. The red pigmentation may have masked the virus symptoms as a bronzing of the leaf margin could be normal for the variety, or might indicate virus infection.
Several green-leafed varieties also had low scores for BWYV intensity, including Alto, Balisto, Canasta, Cindy, Divina, Fanfare, Krizet, Loriol, Nancy, Royal Green, Slobolt, and Waldmann's Green. These varieties represent a wide range of leaf types. In the case of Alto, Cindy, and Slobolt, the pale to cream yellow color of the leaves may also have masked the expression of the virus.
Varieties with high (4.0 or higher) overall scores included Balisto (butterhead), Brunia and Raisa (red oakleaf), Canasta (French crisp), Krizet (oakleaf), Majestic Red (red romaine), New Red Fire and RedPrize (red leaf).
As no insecticides were used, many plants suffered from intense damage caused by diabrotica and other chewing insects. Varieties differed in susceptibility to insect damage. Insect damage was not scored, but the comments note those with severe damage. Most varieties were adapted to the climate and daylength of the Willamette Valley in early summer. However, several varieties did bolt (form an elongated seed stalk) before reaching market maturity, notably Etna and Musca. Varieties of particular interest in future trials include those green leaf, romaine, and butterhead types (listed above) with a low percentage and intensity of BWYV. Their market acceptance will also have to be determined. In general, the spinach varieties showed much less diversity in type and in expression of BWYV than did the lettuce. The degree of virus expression was great for most varieties, although Bejo 1299 and NIZ 46-17 were the slowest to express it and appeared most promising (Table 2). Perhaps the most valuable observation from this trial is the large difference among varieties in tendency to bolt. Bejo 1299, Correnta, Bejo 1369 and 1370, Martine, Space, and Splendour appeared particularly resistant to bolting and may be well-adapted as a summer crop in the Willamette Valley. The color of Splendour, Correnta, 1369, and 1370 was particularly outstanding.
In the autumn spinach planting (Table 3), bolting was not observed in any variety. BWYV intensity was, again, very high with only Fall Green, 1370, NIZ 46-17, and Splendour showing promise when rated on 26 September. Observations were made again on 11 October. At this time, all varieties expressed intense BWYV symptoms (data not shown).
1992
As in 1991, lettuce varieties differed greatly in expression of BWYV virus symptoms (Table 4). Again, many of the varieties with a low score for BWYV intensity were red-pigmented leaf or Romaine types.
Several green-leafed varieties also had low scores for BWYV intensity, including Alto, Balisto, Canasta, Cindy, Divina, Enza 5879, Fanfare, Krizet, Royal Green, Soraya, and Waldmann's Green. Varieties showing consistently low scores (1.5 or less) for BWYV symptoms in both years included Alto, Balisto, Brunia, Canasta, Cindy, Deep Red, Garnet, Krizet, Majestic Red, Musca, New Red Fire, Prizehead, Raisa, RedPrize, Sierra, and Waldmann's Green.
Varieties with high (4.0 or higher) overall scores in 1992 included Balisto and Divina (butterhead); Brunia and Raisa (red oakleaf); Canasta and Sierra (French crisp); Majestic Red (red romaine); New Red Fire, Deep Red, Garnet, Prizehead, and RedPrize (red leaf). All but Divina, Sierra, Deep Red, Prizehead, and Garnet were also rated 4.0 or higher in 1991.
Several varieties bolted (formed an elongated seed stalk) just after reaching market maturity, notably Fanfare, Musca, and Royal Green.
Again, spinach varieties showed much less diversity in type and in expression of BWYV than did the lettuce (Table 5). The degree of virus expression was high for most varieties, although Ambassador, Hybrid #7, NIZ 46-17, Rainier, and Rhythm 9 expressed the symptoms to a lesser degree. These varieties also had a paler color, possibly obscuring symptoms. As in 1991, there were large differences among varieties in tendency to bolt. Bejo 1369, Martine, and Splendour appeared particularly resistant to bolting. The color of Martine was particularly outstanding.
Table 1. Lettuce beet western yellows virus variety trial, NWREC and OSU Vegetable Farm, 1991 Variety Source Type Color BWYV %BWYV Bolting Overall Comments Alpi Nunz Ry 3.5x 4.0 45w 1.0 3.0 Very little insect damage. Alto RZ L 1.5 1.5 5 1.0 3.0 Pale. Anuenue Ter FC 2.3 3.7 35 1.7 2.0 Severe insect damage. Aquarius Sak B 3.8 3.3 21 1.0 3.0 Augustus Peto R 2.8 2.5 38 1.0 3.0 Spreading habit. Balisto RZ B 4.5 1.0 0 1.0 4.5 Bellagreen FM B 3.8 3.0 33 1.0 3.0 Brunia Ter RO 4.3 1.0 2 1.0 4.7 Attractive; very little insect damage. Bubbles Toz BR 2.8 3.5 58 1.0 2.3 Canasta Ter FC 2.8 1.3 21 1.0 4.0 Attractive; some insect damage. Centennial Joh FC 3.3 2.8 40 1.0 2.0 Cindy Ter B 2.3 1.3 28 1.8 3.0 Pale, cream-yellow; severe insect damage. Corsair Toz R 3.3 3.8 39 1.0 2.0 Upright habit; severe insect damage. Cosmic Toz R 3.5 4.0 46 1.0 2.0 Severe insect damage and virus expression. Dark Green Boston Asg B 3.0 3.3 27 1.0 1.7 Severe virus expression. Deep Red HM RL 4.0 1.0 21 2.0 3.3 Density Toz BR 4.0 4.0 40 2.0 2.3 Spreading habit. Divina Vil B 2.0 1.7 29 1.0 3.0 Severe insect damage; poor emergence. E5879 Enza B 2.8 2.5 27 1.0 3.0 Moderate insect damage; one lettuce mosaic. Eline Joh B 2.8 2.3 47 1.0 2.3 Severe insect damage. Etna Vil RL 4.0 1.0 7 4.3 1.3 Bolts too readily. Fanfare FM L 3.0 1.8 34 2.3 2.7 Virus-infected leaves are trimmable. Felicia Enza B 2.5 3.5 49 2.0 1.7 Severe insect damage. Garnet FM RL 4.8 1.0 1 2.3 2.7 Gento Nun B 3.3 3.8 39 1.0 2.0 Severe insect damage and virus expression. Green Towers HM R 3.3 3.0 41 1.0 2.0 Spreading habit. HMX 9561 HM R 3.3 2.5 25 1.0 2.3 Spreading habit. Kagran Summer Joh B 2.3 4.0 63 1.0 1.7 Severe insect damage and virus; poor color. Krizet RZ O 2.0 1.0 0 1.0 4.0 Lobjoits Toz R 4.0 3.5 40 1.0 2.0 Severe insect damage. Loriol Enza B 2.3 1.3 39 1.0 3.7 Moderate insect damage; low vigor. Majestic Red Ter RR 4.8 1.0 8 1.0 4.0 Musca Vil RL 4.8 1.0 4 3.5 2.0 Low vigor; internal tipburn; poor germ. NIZ 739 NZ B 2.0 3.0 40 1.0 2.3 Severe insect damage; pale. NIZ 740 NZ B 2.3 2.3 34 1.0 2.3 Severe insect damage. Nancy Joh B 2.0 1.5 35 1.0 3.0 Severe insect damage. New Red Fire Tak RL 5.0 1.0 6 1.0 4.3 Very deep red. Parris Island Cos Joh R 3.5 3.0 30 1.0 3.0 Spreading habit. Prizehead HM RL 3.8 1.0 8 2.0 2.7 Raisa RZ RO 5.0 1.0 0 1.0 5.0 Attractive; leathery leaf. RedPrize FM RL 4.0 1.0 15 1.0 4.7 Romea Joh R 3.0 4.0 58 1.0 2.0 Romulus Peto R 3.3 3.0 39 1.0 2.3 Royal Green RS L 3.8 1.8 25 1.3 3.7 Salinas HM C 3.3 4.0 28 1.0 2.0 Poor emergence. Sergio Enza R 3.3 4.0 50 1.3 1.3 Severe virus expression. Sierra Vil RF 2.0 1.5 39 1.0 3.0 Moderate insect damage. Slobolt Joh L 1.8 1.0 34 1.0 3.0 Very yellow leaf. Soraya RZ B 2.5 2.0 14 1.0 3.0 Sudia Vil B 4.3 2.5 40 1.0 1.7 Dark green; poor emergence. Summertime OSU C 3.0 3.5 40 1.0 3.0 Tania HM B 3.3 2.8 43 1.0 2.0 Poor emergence. Vanity Enza FC 2.0 2.0 58 1.0 3.3 Rib blight, tipburn; yellow leaf masks virus. Verte Mar Vil R 3.8 3.8 56 1.0 2.7 Severe virus; upright, self-blanching. Victoria Joh FC 3.8 2.0 38 1.0 3.0 Vista Vil B 2.5 2.5 49 1.0 2.3 Cream yellow; severe insect damage. Waldmann's Green Asg L 4.3 1.5 28 2.3 2.3 Winter Density Ter BR 4.3 3.0 41 1.0 2.3 zAsg, Asgrow Seed Co.; Enza, Enza Zaden; FM, Ferry-Morse; HM, Harris-Moran; Joh, Johnny's Selected Seeds; NZ, Nickerson-Zwaan; Nun, Nunhem's; OSU, Oregon State University Dept. of Horticulture; Peto, PetoSeed; RS, Royal Sluis; RZ, Rijk Zwaan; Sak, Sakata; Ter, Territorial Seed Co.; Toz, Tozer Seeds; Vil, Vilmorin. yR, Romaine; L, Leaf; C, Crisphead; O, Oak Leaf; B, Butterhead or Bibb; FC, French Crisp; RR, Red Romaine; RL, Red Leaf; RC, Red Crisphead; RF, Red French Crisp; RO, Red Oak Leaf; RB, Red Butter; BR, Butter-Romaine. xColor, bolting, overall score, and beet western yellows symptom intensity rated on a 5-point scale with 1=least intense, 5=most intense expression of the characteristic. wPercentage of plants expressing virus symptoms, regardless of intensity. Table 2. Summer spinach beet western yellows virus variety trial, NWREC and OSU Vegetable Farm, 1991 Variety Source Type Color BWYV Bolting Comments Ambassador Asgz SSy 3.0x 4.5 4.3 Avon AC SS 3.3 4.8 4.0 B1299 Bejo SS 3.0 3.0 1.0 Resists bolting. Chinook II AC SS 1.8 5.0 5.0 Coho AC SS 3.3 4.8 4.5 Correnta RS F 4.3 4.3 1.0 Resists bolting; some chlorotic mottle. Fall Green AC SS 2.8 3.8 5.0 Grandstand Asg SS 3.3 4.3 5.0 Hybrid 1369 Bejo SS 4.3 3.3 1.0 Resists bolting. Hybrid 1370 Bejo SS 4.5 4.5 1.0 Hybrid 7 AC SS 2.0 4.3 3.8 Some chlorotic mottle. Hybrid CX5013 AC SS 3.7 4.7 3.3 Iron Prince FM F 3.0 4.8 3.5 Some chlorotic mottle. Liberty FM F 2.8 4.0 4.0 Martine RZ S 3.5 3.5 1.0 Melody Twi S 3.3 3.5 3.0 NIZ 46-17 NZ S 1.5 2.8 4.8 Interveinal chlorosis. Rainier AC F 2.7 3.3 5.0 Rhythm 9 RS SS 3.3 4.3 5.0 Skookum AC SS 3.3 5.0 4.5 Some chlorotic mottle. Space Bejo F 3.3 4.5 2.0 Some chlorotic mottle; stunted. Splendour Bejo F 4.3 5.0 1.8 Resists bolting. Tyee AC SS 3.3 5.0 4.3 Vienna AC S 3.5 4.0 5.0 Winter Bloomsdale AC S 4.0 3.5 4.7 zAC, Alf Christianson; Asg, Asgrow; Bejo, Bejo Zaden; FM, Ferry-Morse; NZ, Nickerson- Zwaan; RS, Royal Sluis; RZ, Rijk Zwaan; Twi, Twilley. yS, Savoy; SS, Semi-savoy; F, Flat or Smooth leaf. xColor, bolting, and BWYV symptom intensity rated on 5-point scale with 1=least intense and 5=most intense expression of the characteristic. Table 3. Autumn spinach beet western yellows virus variety trial, NWREC, 1991 Variety Source Type Color BWYV Bolting Overall Comments Avon ACz SSy 3.0x 4.0 1 2.5 Chinook II AC SS 2.0 3.5 1 2.5 Coho AC SS 2.5 4.5 1 2.5 Correnta RS F 3.0 3.0 1 2.5 Fall Green AC SS 2.5 2.0 1 3.0 Small leaves. Hybrid 1369 Bejo SS 3.0 3.5 1 3.5 Poor stand; prostrate habit. Hybrid 1370 Bejo SS 3.0 2.5 1 2.5 Poor stand. Hybrid 7 Bejo SS 3.0 4.0 1 2.5 Good vigor. Hybrid CX5013 AC SS 2.5 3.5 1 2.0 Small leaves; poor vigor. Iron Prince FM F 2.0 4.5 1 2.0 Leaf dieback; mildew-like symptoms. Liberty FM F 2.5 3.0 1 2.5 Good vigor; large leaf. Martine RZ S 3.5 3.0 1 2.5 Melody Twi S 3.0 3.0 1 2.5 NIZ 46-17 NZ S 2.5 2.5 1 3.0 Rainier AC F 2.5 3.5 1 2.0 Rhythm 9 RS SS 3.0 3.0 1 3.0 Skookum AC SS 2.0 5.0 1 1.5 Splendour Bejo F 3.0 2.5 1 3.0 Tyee AC SS 2.5 3.5 1 2.0 Small leaves; poor vigor. Vienna AC S 2.0 3.5 1 2.5 Winter Bloomsdale AC S 3.0 3.5 1 3.0 zAC, Alf Christianson; Bejo, Bejo Zaden; FM, Ferry-Morse; NZ, Nickerson-Zwaan; RS, Royal Sluis; RZ, Rijk Zwaan; Twi, Twilley. yS, Savoy; SS, Semi-savoy; F, Flat or Smooth leaf. xColor, bolting, beet western yellows virus intensity, and overall score on a 5-point scale with 1=least intense and 5=most intense. Table 4. Lettuce beet western yellows virus variety trial, NWREC, 1992 Variety Source Type Color intensity BWYV %BWYV Bolting Overall Alpi Nunz Ry 3.0x 1.5 17w 1.0 3.5 Alto RZ L 2.0 1.5 25 1.0 2.5 Balisto RZ B 4.5 1.0 0 1.5 4.0 Brunia Ter RO 4.0 1.0 2 1.0 4.0 Canasta Ter FC 4.0 1.5 13 1.0 4.0 Cindy Ter B 2.5 1.5 50 1.0 3.0 Cosmic Toz R 3.7 2.7 23 1.0 3.0 Dark Green Boston Asg B 4.0 2.3 35 2.0 3.0 Deep Red HM RL 4.0 1.0 21 3.0 4.0 Density Toz BR 4.0 2.3 20 1.3 3.3 Divina Vil B 3.0 1.7 0 1.0 4.0 E5879 Enza B 3.0 1.0 0 1.0 3.0 Fanfare FM L 3.3 1.0 0 2.3 3.0 Garnet FM RL 4.5 1.0 0 2.0 4.5 Green Towers HM R 3.0 2.7 33 1.3 3.0 HMX 9561 HM R 4.0 2.0 16 1.0 3.5 Kagran Summer Joh B 3.5 4.0 67 1.5 2.0 Krizet RZ O 2.5 1.5 19 1.0 2.5 Loriol Enza B 3.3 2.3 17 1.0 2.7 Majestic Red Ter RR 5.0 1.0 0 1.0 5.0 Musca Vil RL 4.0 1.0 0 4.3 1.7 Nancy Joh B 2.0 2.0 42 1.0 3.0 Nevada Vil FC 2.8 2.3 25 2.0 2.8 New Red Fire Tak RL 5.0 1.0 0 1.3 4.8 Parris Island Cos Joh R 3.8 1.8 20 1.5 3.8 Plato Peto BR 3.8 2.3 19 1.0 2.5 Prizehead HM RL 3.8 1.0 0 1.3 4.0 Raisa RZ RO 5.0 1.0 0 1.0 5.0 RedPrize FM RL 4.3 1.0 0 1.3 4.0 Royal Green RS L 3.8 1.5 13 4.0 3.5 Sierra Vil RF 3.7 1.3 17 1.0 4.0 Slobolt Joh L 2.7 2.3 44 1.0 3.5 Soraya RZ B 3.3 1.0 0 1.0 3.7 Waldmann's Green Asg L 3.8 1.5 25 1.5 3.5 zAsg, Asgrow Seed Co.; Enza, Enza Zaden; FM, Ferry-Morse; HM, Harris-Moran; Joh, Johnny's Selected Seeds; Nun, Nunhem's; Peto, PetoSeed; RS, Royal Sluis; RZ, Rijk Zwaan; Ter, Territorial Seed Co.; Toz, Tozer Seeds; Vil, Vilmorin. yR, Romaine; L, Leaf; C, Crisphead; O, Oak Leaf; B, Butterhead or Bibb; FC, French Crisp; RR, Red Romaine; RL, Red Leaf; RF, Red French Crisp; RO, Red Oak Leaf; RB, Red Butter; BR, Butter-Romaine. xColor, bolting, overall score, and beet western yellows symptom intensity rated on a 5-point scale with 1=least intense, 5=most intense expression of the characteristic. wPercentage of plants expressing virus symptoms, regardless of intensity. Table 5. Spinach beet western yellows virus trial, NWREC, 1992 Variety Source Type Color intensity BWYV Bolting Overall Ambassador Asgz SSy 4x 3 5 2 Avon AC SS 3 4 5 2 Coho AC SS 3 4 5 2 Correnta RS F 4 5 2 3 Hybrid 1369 Bejo SS 4 5 1 3 Hybrid 1370 Bejo SS 4 5 2 3 Hybrid 7 AC SS 2 3 5 1 Hybrid CX5013 AC SS 3 4 5 1 Liberty FM F 2 4 5 1 Martine RZ S 5 5 1 2 Melody Twi S 4 4 4 2 NIZ 46-17 NZ S 3 3 5 2 Rainier AC F 2 3 5 1 Rhythm 9 RS SS 2 3 5 1 Space Bejo F 4 5 3 2 Splendour Bejo F 4 5 1 3 Vienna AC S 3 5 5 2 Winter Bloomsdale AC S 3 4 5 2 zAC, Alf Christianson; Asg, Asgrow; Bejo, Bejo Zaden; FM, Ferry-Morse; NZ, Nickerson-Zwaan; RS, Royal Sluis; RZ, Rijk Zwaan; Twi, Twilley. yS, Savoy; SS, Semi-savoy; F, Flat or Smooth leaf. xColor, bolting, and BWYV symptom intensity rated on 5-point scale with 1=least intense and 5=most intense expression of the characteristic.