Resistance to curly top of sugar beet in germplasm developed at USDA-ARS Ft. Collins, 2013

Seventy-one sugar beet (Beta vulgaris L.) lines from the USDA-ARS Ft. Collins sugar beet program and three control lines were screened for resistance to Beet curly top virus (BCTV) in 2013. Commercial cultivars ‘Monohikari’ (susceptible), ‘HM PM90’ (resistant) and Betaseed line Beta G6040 (resistant) were included as controls. The curly top evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID, and was grown using typical agronomic practices. The plots were two rows 10 ft long with 22-in row spacing and arranged in a randomized complete block design with four replications. Plants were inoculated at the four- to six-leaf growth stage on June 27 with approximately six viruliferous beet leafhoppers per plant. The beet leafhoppers were redistributed twice a day (immediately after sunrise and just before sunset) for one week by dragging a tarp through the field to disrupt settled/feeding leafhoppers. The plots were rated for foliar symptom development on July16 using a scale of 0-9 (0 = healthy and 9 = dead), with the scale treated as a continuous variable. Data were analyzed using the general linear models procedure, and Fisher’s protected least significant difference (a = 0.05) was used for mean comparisons. Development of curly top disease symptoms was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was severe with good symptom development in the susceptible control. Beta G6040, HM P90, and Monohikari were rated at 4.2, 4.4, and 6.3, respectively. The field was confirmed to be predominantly infected with Beet curly top virus (BCTV) and Beet severe curly top virus (BSCTV), with minimal infection by Beet mild curly top virus (BMCTV), using species-specific PCR. Thirty-five entries tested were not significantly different from the resistant control (Beta G6040) based on visual symptoms but were significantly better than the susceptible control (Monohikari). Of those 35 entries, 15 were germplasm being evaluated for release based on a number of factors, including resistance to curly top. Decisions to release these germplasm to commercial plant breeders will be based on their total performance, including resistance to curly top. Among the 35 best performing entries were 20 selfed single plant families of the cross (07-FC1015-420/C833-5cms)/FC201. The top 3 of the resistant families based on severity scores will be grown from remnant seed, recombined, tested against other pathogens, and further developed for eventual release as enhanced germplasm to commercial breeders and other researchers

Beet curly top resistance in USDA-ARS Ft. Collins germplasm, 2016

Fifty-one sugar beet (Beta vulgaris L.) germplasm lines produced by the USDA-ARS Ft. Collins sugar beet program and three commercial check cultivars [SV2012RR (susceptible) and HM PM90 and Beta G6040 (resistant)] were screened for resistance to Beet curly top virus (BCTV). The curly top evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID which has Portneuf silt loam soil and had been in barley in 2015. The field was plowed in the fall and in the spring, it was fertilized (90 lb N and 110 lb P2O5/A) and roller harrowed on April 4. The germplasm was planted (density of 142,560 seeds/A) on May 16. The plots were two rows 10 ft long with 22-in row spacing and arranged in a randomized complete block design with four replications. The field was sprinkler irrigated, cultivated, and hand weeded as necessary. Plant populations were thinned to about 47,500 plants/A on June 16. Plants were inoculated at the four- to six-leaf growth stage on June 20th with approximately six viruliferous (contained at least the following BCTV strains: Cal/Logan, CO, Severe, and Worland) beet leafhoppers per plant. The beet leafhoppers were redistributed three times a day during the first two days and then twice a day for five more days by dragging a tarp through the field. The plants were sprayed on June 30th with Lorsban 4E (1.5 pints/A) to kill the beet leafhoppers. Plots were rated for foliar symptom development on July 13th using a scale of 0 to 9 (0 = healthy and 9 = dead), with the scale treated as a continuous variable (Plant Dis. 90:1539-1544). Data were analyzed in SAS using the general linear models procedure (Proc GLM), and Fisher’s protected least significant difference (LSD; a = 0.05) was used for mean comparisons. Curly top symptom development was uniform and no other disease problems were evident in the plot area. The resistant and susceptible checks performed as expected for the visual ratings. Based on the visual rating, seven entries (1, 14, 15, 32, 40, 44, and 51) were not significantly different from the resistant check. These germplasm will be retested and, if resistance is confirmed, they may be incorporated into the USDA-ARS germplasm improvement program as sources of resistance to BCTV. These results and germplasm will be accessible to interested parties through the USDA-ARS, NPGS GRIN database (http://www.ars-grin.gov/npgs/index.html)

Strausbaugh, C.A., Panella, L.W. 2016. Beet curly top resistance in USDA-ARS plant introduction lines, 2015

Curly top caused by Beet curly top virus (BCTV) is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem, but resistance in commercial cultivars is only low to intermediate. In order to identify novel sources of curly top resistance, thirty-one Plant Introduction (PI) Lines were screened in a disease nursery in 2015. The lines were arranged in a randomized complete block design with three replications. A curly top epiphytotic was created by releasing approximately 6 viruliferous beet leafhoppers per plant at the four- to six-leaf growth stage on 24 Jun. Foliar symptoms were evaluated on 13 and 20 Jul using a scale of 0-9 (0 = healthy and 9 = dead) in a continuous manner. Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was moderately severe with good symptom development in the susceptible check. Seven of the PIs were not significantly different from the resistant checks based on the overall visual symptom rating. These promising lines will be retested and, if resistance is confirmed, they will be incorporated into the USDA-ARS sugar beet germplasm improvement program as potentially novel sources of resistance to BCTV

Beet curly top resistance in USDA-ARS plant introduction lines, 2016

Curly top caused by Beet curly top virus (BCTV) is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem, but resistance in commercial cultivars is only low to intermediate. In order to identify novel sources of curly top resistance, twenty-nine Plant Introduction (PI) Lines were screened in a disease nursery in 2016. The lines were arranged in a randomized complete block design with four replications. A curly top epiphytotic was created by releasing approximately six viruliferous beet leafhoppers per plant at the four- to six-leaf growth stage on 20 Jun. Foliar symptoms were evaluated on 13 Jul using a scale of 0-9 (0 = healthy and 9 = dead) in a continuous manner. Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was moderately severe with good symptom development in the susceptible check. Three of the PIs were not significantly different from the resistant checks based on the visual rating. These promising lines have been incorporated into the USDA-ARS sugar beet germplasm improvement program as potentially novel sources of resistance to BCTV

Ft. Collins sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2012

Rhizomania caused by the Beet necrotic yellow vein virus (BNYVV) is a worldwide problem that can lead to loss of tonnage and lower percent sucrose in the field. BNYVV can also reduce the storability of roots. To identify germplasm with resistance to these problems, 18 sugarbeet germplasm lines developed by the USDA-ARS Ft. Collins sugarbeet program and four check cultivars were screened in a field experiment arranged in a randomized complete block design with 6 replications. During the growing season plants were evaluated for foliar rhizomania symptoms. At harvest on 4 October 2012, roots were evaluated for rhizomania symptoms and then placed into an indoor commercial sugarbeet storage building in Paul, ID. Foliar symptoms ranged from 0% for resistant checks to 95% for the susceptible check, indicating good separation of germplasm for BNYVV resistance should have been possible in the field study. BNYVV root ratings ranged from a low of 19 for a resistant check to a high of 32 for one of the susceptible entries at harvest. Fungal growth on the root surface in storage ranged from a low of 12% for an entry with good storability to a high of 71% for the BNYVV susceptible check. Entries 11, 12, and 15 performed well for all variables. Incorporating better resistance to BNYVV and good storability into commercial sugarbeet cultivars should allow for increased yields in the field and improved recovery of sucrose from roots in storage

Beet curly top resistance in USDA-ARS Plant Introductions, 2012

Thirty sea beet (Beta vulgaris subsp. maritima (L.) Arcang) and beet (Beta vulgaris subsp. vulgaris L.) plant introduction (PI) accessions from the Beta collection of the USDA-ARS National Plant Germplasm System were screened for resistance to Beet severe curly top virus (BSCTV) and other closely related Curtovirus species in 2012. Commercial cultivars Monohikari and HM PM90 and Betaseed, Inc. germplasm line G6040 were included as susceptible and resistant checks. The curly top evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID which has Portneuf silt loam soil and had been in alfalfa in 2011. The field was plowed in the fall and in the spring, fertilized (90 lb N and 110 lb P2O5/A) on 16 Apr 12, sprayed with Ethotron (2 pt/A), and roller harrowed. The germplasm was planted (density of 142,560 seeds/A) on 21 May. The plots were two rows 10 ft long with 22-in row spacing and arranged in a randomized complete block design with three replications. The fields were sprinkler irrigated and hand weeded as necessary. Plant populations were thinned to about 47,500 plants/A on 19 Jun. Plants were inoculated at the four to six leaf growth stage on 22 Jun with six viruliferous beet leafhoppers per plant. The beet leafhoppers were moved twice a day (right after sunrise and just before sunset) for one week by dragging a tarp through the field. The plants were sprayed with Lorsban 4E (1.5 pints/A) on 4 Jul to kill the beet leafhoppers. The plots were rated for foliar symptom development on 10 Jul using a scale of 0-9 (0 = healthy and 9 = dead; Mumford 1974), with disease index (DI) treated as a continuous variable. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher’s protected least significant difference was used for mean comparisons. Disease development was uniform and other disease problems were not evident in the plot area. The disease pressure in the test was severe with good disease development in the more susceptible lines. Most of the lines were not significantly different from the most resistant check. These accessions will be retested and, if the resistance is confirmed, entered into USDA-ARS breeding programs to enhance sugar beet germplasm with increased resistance to Beet severe curly top virus (BSCTV) and other closely related Curtovirus species. These data will be entered into the USDA-ARS, NPGS GRIN database (http://www.ars-grin.gov/npgs/index.html)

Sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2011.

Rhizomania caused by the Beet necrotic yellow vein virus (BNYVV) is a worldwide problem that can lead to loss of tonnage and lower percent sucrose in the field. BNYVV can also reduce the storability of roots. To identify germplasm with resistance to these problems, 14 sugarbeet germplasm lines developed by the USDA-ARS Ft. Collins sugarbeet program were screened in a field experiment arranged in a randomized complete block design with 5 replications. During the growing season plants were evaluated for foliar rhizomania symptoms. At harvest on 29 September, roots were evaluated for rhizomania symptoms and then placed into an indoor commercial sugarbeet storage building in Paul, ID. Foliar symptoms ranged from 0% for one of the resistant checks to 99% for the susceptible check, indicating good separation of germplasm for BNYVV resistance should have been possible in the field study. BNYVV root symptoms ranged from a low of 14 for a resistant check to a high of 25 for one of the susceptible entries at harvest. Fungal growth on the root surface in storage ranged from a low of 21% for an entry with good storability to a high of 100% for the BNYVV susceptible check. Entry 6 ranked among the best entries for all variables indicating it should be investigated further as a potential source of good resistance to these problems. Incorporating better resistance to BNYVV and good storability into commercial sugarbeet cultivars should allow for increased yields in the field and improved recovery of sucrose from roots in storage

Beet curly top resistance in USDA-ARS Plant Introductions, 2013

Curly top caused by Curtovirus species is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem but resistance in commercial cultivars is only low to intermediate. In order to identify novel sources of curly top resistance, thirty Plant Introduction (PI) Lines were screened in a disease nursery in 2013. The lines were arranged in a randomized complete block design with three replications. A curly top epiphytotic was created by releasing approximately 6 viruliferous beet leafhoppers per plant at the four- to six-leaf growth stage on 27 Jun. Foliar symptoms were evaluated on 16 Jul using a scale of 0-9 (0 = healthy and 9 = dead) in a continuous manner. Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was moderately severe with good symptom development in the susceptible check. Twelve of the PIs were not significantly different from the resistant control, HM PM90. Of these 12 PIs, three performed extremely well, one from Greece (PI546423) and two from Portugal (PI604524, PI604539). They will be retested and, if resistance is confirmed, they will be incorporated into the USDA-ARS germplasm improvement program as potentially novel sources of resistance to BSCTV and closely related Curtovirus species

Beet curly top resistance in USDA-ARS Ft. Collins Germplasm, 2011

Twenty-two sugar beet (Beta vulgaris L.) lines from the USDA-ARS Ft. Collins sugar beet program were screened for resistance to Beet severe curly top virus (BSCTV) and other closely related Curtovirus species in 2011. Commercial cultivars Monohikari and HM PM90 were included as susceptible and resistant checks, respectively. The curly top evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID which has Portneuf silt loam soil and had been in barley in 2010. The field was plowed both in the fall and the spring, fertilized (80 lb N and 120 lb P2O5/A) on 20 Apr 11, sprayed with Ethotron (2 pt/A), and roller harrowed. The germplasm was planted (density of 142,560 seeds/A) on 16 May. The plots consisted of two rows 10 ft long with 22-in row spacing, arranged in a randomized complete block design with three replications. The field was sprinkler irrigated and hand-weeded as necessary. Plant populations were thinned to about 47,500 plants/A on 19 Jun. Plants were inoculated at the four to six leaf growth stage on 27 Jun with approximately six viruliferous beet leafhoppers per plant. The leafhoppers had been reared in the greenhouse on viruliferous sugar beet plants. The beet leafhoppers were moved twice a day (right after sunrise and just before sunset) for 1 week by dragging a tarp through the field. The plants were sprayed with Lorsban 4E (1.5 pints/A) on 11 Jul to kill the beet leafhoppers. The plots were rated for foliar symptom development on 18 Jul using a scale of 0-9 (0 = healthy and 9 = dead; Mumford 1974), with disease index (DI) treated as a continuous variable. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher’s protected least significant difference was used for mean comparisons. Yield data were not collected. Curly Top development was uniform and no other disease problems were evident in the plot area. The test was evaluated while disease pressure was moderate and good symptom development occurred in the more susceptible lines. The experiment was rated only 3 weeks after inoculation, because of the severity of the epidemic; some of the more susceptible entries had died by 4 weeks and thus some of the differences among entries were no longer apparent. Only three experimental germplasms and the susceptible check were significantly different from the resistant controls. However, the three most resistant germplasm tested were not significantly different from the most resistant control (HM PM90, rated 3.1). All three also have increased tolerance of leaf spot caused by Cercospora beticola Sacc. (data not shown). The combination of resistance to both diseases gives this germplasm potential for use in development of hybrid parents in the Great Plains (Colorado, Wyoming, Western Nebraska, and Montana) because both of these diseases can severely limit yield. These lines also may be of use in the Red River Valley of North Dakota and Minnesota, as well as Michigan, two growing areas with severe leaf spot pressure

Ft. Collins sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2012

Rhizomania caused by the Beet necrotic yellow vein virus (BNYVV) is a worldwide problem that can lead to loss of tonnage and lower percent sucrose in the field. BNYVV can also reduce the storability of roots. To identify germplasm with resistance to these problems, 18 sugarbeet germplasm lines developed by the USDA-ARS Ft. Collins sugarbeet program and four check cultivars were screened in a field experiment arranged in a randomized complete block design with 6 replications. During the growing season plants were evaluated for foliar rhizomania symptoms. At harvest on 4 October 2012, roots were evaluated for rhizomania symptoms and then placed into an indoor commercial sugarbeet storage building in Paul, ID. Foliar symptoms ranged from 0% for resistant checks to 95% for the susceptible check, indicating good separation of germplasm for BNYVV resistance should have been possible in the field study. BNYVV root ratings ranged from a low of 19 for a resistant check to a high of 32 for one of the susceptible entries at harvest. Fungal growth on the root surface in storage ranged from a low of 12% for an entry with good storability to a high of 71% for the BNYVV susceptible check. Entries 11, 12, and 15 performed well for all variables. Incorporating better resistance to BNYVV and good storability into commercial sugarbeet cultivars should allow for increased yields in the field and improved recovery of sucrose from roots in storage