Tomato Spotted Wilt Virus: TSWV in Vegetable Crops: Tospoviruses

Tospoviruses In Solanaceae and Other Crops in The Coastal Plain of Georgia

Management of TSWV

Evaluation of Breeding Lines and Cultivars for Tomato Spotted Wilt Resistance in Georgia

Mike Stephenson, Steve LaHue, Jennifer Levin-Nicholson, Verne Sisson

Since the USDA-ARS withdrew from tobacco research in 1995, cooperators continued with personnel from NC State (Dr. Verne Sisson), to screen some lines based on Polata, which is resistant to TSWV. In 1997 various lines of GMO K326, which had resistance to TSWV, were screened in cooperation Dr. Jennifer Levin.

In 2001 to encourage breeders to work on TSWV, up to 20 lines with 10 replications depending on participators were screened for no cost. Data from 14 plant plots were taken from 10 plants, which would include the percentage TSWV, harvestable plants and vigor per plot rated 1-10, 10 being the best. Any outstanding lines would be added to the Official Variety Test for yield and quality.

2001 season

In the 2001 season, Dr. Sisson’s test consisted of 20 entries of breeding lines 1401-1415, Polata, K326, OX 207, NC 95 and C 371G. Dr. Levin’s test consisted of five replications of ten entries which included K326, non- transgenic susceptible control, Polata, NM 13 R1, NM13 R2, NM 13 R3, NM 13 R4, NM 70 R1, NM 70 R2, NM 70 R3, and NM 70 R4. The lines NM 13 and NM 70 have been transformed with the TSWV nucleocapsid gene and R1, R2, R3 and R4 refers to the generation of seeds.

In Dr. Sisson’s test efforts were under way to transfer resistance to TSWV from an air cured variety named Polata into flue-cured tobacco using conventional breeding methods. Stable lines from several cycles of crossing and selections were tested. In 2001, 11 F 1 hybrid combinations and four advanced generation breeding lines were tested for resistance to TSWV under field conditions. The resistant check Polata, entry 1415 showed similar results to Polata, 8 percent TSWV vs. 5 percent TSWV respectively, with untreated K326 at 28 percent TSWV. Though entries 1409, 1413 had 86 percent and 76 percent harvestable plants, and the amount of TSWV at 20 percent, it was important to identify material for further development. Dr. Levins’ test lines that were initially resistant to TSWV were advanced for four generations, and several resistant lines were found to develop systemic symptoms in greenhouse tests in later generations indicating susceptibility to TSWV. As these lines were double haploids, and therefore completely homozygous, segregation of the transgene was not the cause of susceptibility. In these cases the transgene appears to become inactivated, resulting in the loss of virus resistance. In 2001, the first through fourth generations of two lines that showed a loss of resistance were planted in Tifton, Georgia, to determine if these lines showed a decline in TSWV resistance in the field as well.

In greenhouse tests both NM 13 and NM 70 were completely resistant to TSWV in the R1 and R2 generations. In the R3 generation about half the plants were susceptible to TSWV. NM 70 still retained some resistant plants in the R4, but all the plants of NM 13 were susceptible to TSWV in the R4. These results were mirrored when these lines were planted in the field. The R1 and R2 generations of both lines showed a very low incidence of TSWV. TSWV incidence was increased for both lines in the R3. In the R4, line NM 13 had a TSWV incidence over that of the susceptible K326, showing that resistance had been completely lost. For NM 70, TSWV incidence was increased in the R4 in comparison to the R3, but was still only a third of the level of the susceptible control.

These data show that virus resistance in the field can decline over generations in some lines, and virus resistant transgenic lines should be tested over several generations to determine the stability of resistance before release to growers.

2002 Season

In the 2002 season with 20 lines of Dr. Sisson of NC State, 2401–2420, were evaluated. The second test included eight flue-cured selections and two burley susceptibility checks for Dr. Guy Gooding, a commercial breeder. These included NC 95, N 95-81, NC 9552, 2009, 2041, 2026, Bull A and Bu 37. The third test was for Dr. Albert Johnson of Clemson University at Pee Dee and consisted of eight lines PD 1-8 based on selections from aphid resistant tobacco introduction.

The 2002 season was the heaviest TSWV season to date at the Bowen Farm with disease rates as high as 80 percent TSWV for untreated K 326. Dr. Sisson’s test, the first to be transplanted, came under heavy pressure. At four weeks after transplanting TN 90, a burley variety which is extremely susceptible, had 72 percent disease and virtually all plants were dead by the end of the season. In less susceptible selections, K 326 had 32 percent diseased plants at four weeks, and 2401 and 2402, advanced breeding lines, had 16 percent and 22 percent diseased plants, respectively. As a result, seed was collected from a number of resistant plants for future testing. Dr. Guy Gooding’s selections with a heritage from NC95 showed some improvement over the susceptible checks. In the final test, Dr. Albert Johnson’s selections based on aphid resistant tobacco introductions ranged from 31 percent disease for Entry 1 to 72 percent disease for Entry 8. The remaining six lines were in the middle with a range of 40 percent to 60 percent disease.

2003 Season

Five replications of thirty entries 3601-3611, 3619- 3625 were evaluated for Dr. Verne Sisson and for Dr. Albert Johnson PD 1-PD 6 for TSWV. The 2003 season was light (around 2%) due to spring rains which delayed planting causing more mature plants to be transplanted. Previous data has shown that rain reduces thrips, mature plants are more resistant, and later transplanting reduces disease. For this test plants were transplanted at the end of March, using young transplants, a 40 percent infection rate was observed at the Bowen Farm for all untreated K 326. Dr. Sisson’s lines 3605 and 3621 had the lowest disease rate of 9.23 percent and 9.81 percent respectively, but were hurt in vigor due to herbicide and cultivation necessary to control nutsedge in the plots. 3601-3604 had good vigor and 16.76 percent and 16.16 percent TSWV, respectively.

Dr. Johnson’s best lines were PD 2, 6.4 percent TSWV and good vigor, PD 5 with 5.55 percent TSWV, PD 7 with 3.35 percent TSWV but middling vigor, PD 8 had 6.23 percent TSWV and good vigor and PD 10 with 6.17 percent TSWV and excellent vigor. In all, both sets of lines have shown dramatic resistance to TSWV compared to the K 326 control, and if introduced into commercial lines could virtually eliminate the economic impact of the disease.

2004 Season

The test in 2004 consisted of five replications of 26 entries, 4255-4270 and Polata for Dr. Verne Sisson of North Carolina State University, PD 1-PD 5 for Dr. Albert Johnson of Clemson University at Pee Dee and four released varieties Speight H 11, OX 207, NC 95 and K 326 all non treated.

The incidence of TSWV at the Bowen Farm was in excess of 50 percent infection. Virtually all of Dr. Verne Sisson’s lines 4255 - 4267 were more than 50 percent TSWV with the exception of 4256 at 40 percent. Entries 4268, 4269, 4270 had 38.9 percent, 17.9 percent, and 28.5 percent, respectively. Plants with less TSWV were more vigorous plants at harvest. The Polata check had 23.9 percent TSWV and only one line of Dr. Sisson’s did better (4269 at 17.9%). NC 95 had 18.6 percent TSWV and showed excellent vigor rating 8.6 out of 10 with10 as the absolute best. In some years, NC 95 will perform well but it is not consistent and previously screened selections from NC95 did not perform uniformly. The commercial line Speight H 11 was 30.4 percent infected, but when treated with an Actigard/ Admire combination in another test had only 7 percent TSWV. Its resistance is based on releases from Dr. Albert Johnson at the Pee Dee station at Florence, South Carolina. Dr. Johnson’s PD 1 and PD 2 demonstrated excellent vigor ratings 7.2 and 8.6 number of harvestable plants at 10.6 and 9.0 and TSWV 20 percent and 31.4 percent respectively. These lines in last year’s test were in the low single digits. Unfortunately, the Regional Variety Committee rejected Speight H 11 based on agronomic characters, so it would not be available to farmers. Resistance does exist just the right combination of agronomic and chemical characters need to be incorporated. GMOs show great promise in solving the TSWV problem if the industry would adopt them.

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