Influence of host resistance and insecticide seed treatments on curly top in sugar beets

Curly top on sugar beets (Beta vulgaris) caused by Beet severe curly top virus or closely related species is a considerable problem in arid growing regions of the western United States. Two insecticide seed treatments, Poncho Beta (60 g a.i. clothianidin + 8 g a.i. beta-cyfluthrin/100,000 seed) and Gaucho (45 g a.i. imidacloprid/100,000 seed), and four sugar beet hybrids varying in curly top resistance were evaluated for their influence on the control of curly top in comparison with untreated checks. Plots were established at two locations in southern Idaho in 2005 and evaluated for curly top. Moderate to severe curly top due to natural inoculum and leafhopper infestations occurred at both locations. Untreated, the four hybrids performed as expected with the fewest curly top symptoms on PM21 and the most on Monohikari. Both insecticide treatments lowered curly top ratings compared with the untreated check, but Poncho Beta reduced symptoms more than Gaucho as the season progressed. Poncho Beta led to increased yield and estimated recoverable sugar across all hybrids at harvest, particularly on the more susceptible hybrids. When considering the yield parameters for only the most resistant hybrids individually, Poncho Beta did not always outperform Gaucho. Poncho Beta provided a level of control that would justify its application as a supplement to host resistance under Idaho conditions

Evaluation of experimental sugar beet hybrids for resistance to curly top in Malheur County, OR, 2005

Twenty-five experimental sugarbeet hybrids submitted to the official variety trials were evaluated for resistance to Beet curly top virus (BCTV). Hybrids were planted in a commercial sprinkler-irrigated sugarbeet field and exposed to a natural epiphytotic of BCTV. Experimental units were arranged in a randomized complete block design with seven replications. Plots were evaluated for BCTV based on a Disease Index (DI) scale of 0 to 9 (no symptoms to dead) on Sept 14, 2004 by three raters. The moderately severe epiphytotic resulted in uniform disease pressure and significant differences between hybrids for DI, root yield, sugar content, and estimated recoverable sugar. Our disease ratings were positively correlated with (r = 0.632, P < 0.0001) ratings from the 2004 Curly Top Nursery. There was no correlation between DI and estimated recoverable sugar which was probably due to field or genetic variation influencing yield

Evaluation of commercial sugar beet hybrids for resistance to curly top in Malheur County, OR, 2005

Commercial sugar beet hybrids were evaluated for resistance to Beet severe curly top virus in a furrow-irrigated sugar beet field near Ontario, OR where curly top had been a problem in previous years. The field trial relied on natural infection and was planted on 6 Apr. Plots were planted to a density of 285,120 seeds/A, and thinned to 40,731 plants/A. Plots were four rows wide (22 in. between rows) and 23 ft long. The experimental design was a randomized complete block with eight replications. The crop was managed according to standard cultural practices. The weather during the growing season was normal except for above average temperatures in Mar and Aug and above average precipitation in Apr and May. Disease pressure was uniform and moderately severe. Disease data were recorded on 16 Sep by three individual raters separately using a disease index of 0 to 9 (0 = no symptoms; 9 = dead plant). The three ratings per plot were averaged prior to analysis. The center two rows were harvested on 13 and 14 Oct using a small plot harvester. Yield data were reduced by 10% to account for tare. Sugar content of the beets was determined by the Amalgamated Sugar Co. laboratory using a polarimeter, and recoverable sugar was estimated based on percent sugar and conductivity. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher's protected LSD was used for mean comparisons. Yields were typical for this site and above average for growers. The commercial hybrids response to Beet severe curly top virus ranged from acceptable (slight leaf curl = 2 to most leaves with moderate curling = 4) to severe (most larger leaves becoming prostrate = 6). Analysis of variance indicated there were significant differences among hybrids for disease index, root yield, sugar content, and estimated recoverable sugar. Based on Spearman's coefficient of rank correlation, our disease ratings positively correlated (r s = 0.82, P < 0.0001) with those from the 2005 Curly Top Nursery in Kimberly, ID. There was an inverse relationship (rs = -0.63, P = 0.0005) between estimated recoverable sugar and disease index

Bacteria and yeast associated with sugar beet root rot at harvest in the Intermountain West

An undescribed wet rot of roots was observed in surveys of recently harvested sugar beet roots in Idaho and eastern Oregon in 2004 and 2005. Microorganisms isolated from 287 roots fell into the following groups: A (41% of strains), B (29%), C (17%), D (11%), E (2%), and F (1%). Groups A, B, C, and F were composed of bacteria while groups D and E were yeasts. Subgroup A1 (80% of group A strains) included Leuconostoc mesenteroides subsp. dextranicum strains and subgroup A2 (20%) contained Lactobacillus strains. Group B was dominated by subgroup B1 (92% of strains), which included Gluconobacter strains. When only one organism was isolated from rotted roots, strains from subgroup A1 were isolated most frequently. Group C was composed of enteric bacteria. Strain B322 of L. mesenteroides subsp. dextranicum caused the most severe rot on root slices and produced symptoms similar to those in harvested roots. Results suggest that L. mesenteroides subsp. dextranicum is among the first bacterial species to enter sugar beet roots, closely following fungal infections or entering directly through openings such as growth cracks. The bacterial rot leads to yield loss in the field but likely also leads to storage and factory-processing problems

USDA-ARS sugar beet germplasm developed in Salinas, CA, evaluated for rhizomania resistance in Idaho

Thirty-one sugar beet germplasm breeding lines and releases produced by the USDA-ARS sugarbeet program at Salinas, CA, and one line from the USDA-ARS sugarbeet program at East Lansing, MI, were evaluated for resistance to rhizomania under south-central Idaho conditions at Twin Falls, ID. The field had been identified as having Beet necrotic yellow vein virus (BNYVV), which overcomes resistance conditioned by the Rzl gene. Single-row plots 10 ft long with 22-in. spacing were planted on 23 May 05. Plants were thinned to 4 to 6-in. spacing in mid-Jun. The materials were predominantly multigerm; they were hand thinned to single plants during the first week of Jul. The trial layout was a randomized complete block with eight replicates, however, the blocks were divided into 16 sub-blocks of six rows in which single-row plots of two entries and four control lines were randomized. The control lines were Beta443OR (Rzl gene), GO17R (Rz2 gene), Angelina (Rzl+Rz2 genes) and Beta6600 (no resistance to rhizomania). This allowed each entry plot to have its own control (Local Control). This was necessary given the uneven distribution in the field of resistance breaking strains of BNYVV. Naturally occurring Curly top virus infection was found throughout the field early in the season. Many plants of the rhizomania susceptible control were killed apparently by curly top and therefore this should be considered when evaluating the results. Plants were scored 19 Sep for curly top using a 0-9 scale with 0 showing no symptoms and 9 being dead. Plants were topped, roots lifted then scored on 12-13 Oct. Four teams evaluated the trial for rhizomania with each team rating two replicates. Each root was scored based on the traditional 0 to 6 scale which was converted to a 0 to 9 scale. The categories were 0, 1, 3, 5, 6, 7 and 9 with 0-3 being resistant, 5-7 susceptible and 9 was dead. The average disease severity was determined to create a disease index (DI) for each entry and control. A second index (DI2) was calculated for each entry-plot to evaluate the entry relative to the mean of the Rz2 and Rzl+Rz2 Local Controls (DI of entry/mean DI of the Rz2 and Rzl+Rz2 Local Controls). The percent healthy roots (categories 0-3 combined) and the percent of healthy roots relative to Rz2 and Rzl+Rz2 Local Controls were calculated (PR and PR2, respectively). The DI and DI2 were transformed with the inverse square root and analyzed using PROC MIXED - SAS with Dunnett's test (P = 0.05) option and PROC GLM – SAS with Fisher's protected LSD test (P = 0.05) option, respectively. PR and PR2 were analyzed with PROC GLM –SAS using Dunnett's test (P = 0.05) and Fisher's protected LSD (P = 0.05) test, respectively. The analysis of variance of DI2 showed that block effects were significant, therefore Spearman's partial correlation (PROC CORR Spearman partial - SAS) was used to analyze the relationship of D1, PR, DI2, PR2, and curly top. PROC CORR Spearman -SAS was used to analyze the relationship between DI and DI2

Evaluation of Beta corolliflora for resistance to curly top in Idaho

Curly top of sugarbeet is caused by Beet severe curly top virus (BSCTV) or closely related curtovirus species which are vectored by the beet leafhopper (Circulifer tenellus). Beta corolliflora, shown in 1969 to impart a very high level of curly top resistance to sugarbeet into the BC2 generation, is a wild relative of cultivated sugarbeet that has not been utilized in breeding programs. The nature of curly top resistance from B. corolliflora seems to be reduced symptoms and resistance to viral accumulation. Field screening of 14 B. corolliflora accessions for resistance to curly top followed by PCR detection of BSCTV did not identify any accessions with phenotypic symptoms of curly top and 9 accessions did not have detectable virus. Clip cage inoculations followed by PCR detection of BSCTV and of related species, Beet mild curly top and Beet curly top viruses, were difficult to interpret due to small sample size but indicated that accessions BETA 408, BETA 414, BETA 528, BETA 690, and BETA 805, from Genebank Gatersleben, Foundation Liebniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany had no visible curly top symptoms or evidence of virus accumulation. Results of a preference test showed that beet leafhoppers did not have a strong aversion to B. corolliflora and likely would have at least sampled the plants in the field. Therefore, field screening for resistance to curly top, at least in the early generations of an introgression program, should be successful

Evaluation of experimental sugarbeet hybrids for resistance to beet curly top in Canyon County, ID, 2004

Experimental sugarbeet hybrids were evaluated for resistance to Beet curly top virus in a commercial sprinkler irrigated sugarbeet field near Nampa, ID where beet curly top had been a problem in previous years. The field trial relied on natural infection and was planted on 19 Mar. The plots were planted to a density of 190,000 seeds/A, and thinned to 35,640 plants/A. Plots were four rows wide (22 in -row spacing) and 36 ft long. The experimental design was a randomized complete block design with seven replications. The crop was managed by the grower according to standard cultural practices. The weather during the growing season was cooler than normal and disease pressure was uniform and moderately severe. Disease data were recorded on 14 Sept by three raters using a disease index of 0 to 9 (no symptoms to dead). The three ratings per plot were averaged prior to analysis. The center two rows were harvested on 20 Oct using a small plot harvester. The sugar content of the beets was determined by the Amalgamated Sugar Co. laboratory, and recoverable sugar (lb/A) was estimated. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher's Protected LSD was used for mean comparisons. Yields were above average and disease pressure was moderately severe. The experimental hybrids response to Beet curly top virus ranged from acceptable (slight leaf curl to most leaves with moderate curling) to moderately affected (severe leaf curling). Analysis of variance indicated there were significant differences among hybrids in disease index, root yield, sugar content, and estimated recoverable sugar. Disease index for hybrids in this test were positively correlated (r s = 0.632, P < 0.0001) with ratings from the 04 Curly Top Nursery in Kimberly, ID. Based on Spearman's Coefficient of Rank Correlation (rs = -0.15, P = 0.4651), there was no correlation between estimated recoverable sugar and disease index. This lack of correlation between estimated recoverable sugar and disease index was likely not related to variation associated with the disease rating but rather due to other factors such as field and genetic variation that influenced yield. B&

Evaluation of commercial sugarbeet hybrids for resistance to beet curly top in Canyon County, ID, 2004

The experiment was conducted in a commercial sprinkler-irrigated sugarbeet field near Nampa, ID in an area where Beet curly top virus had been a problem in previous years. The field trial relied on natural infection and was planted on 19 Mar. The plots were planted to a density of 190,000 seeds/A, and thinned to 35,640 plants/A. Plots were four rows wide (22 in-row spacing) and 36 ft long. The experimental design was a randomized complete block with eight replications. The crop was managed by the grower according to standard cultural practices. The weather during the growing season was cooler than normal. Disease data were recorded on 14 Sept by three raters using a disease index of 0 to 9 (no symptoms to dead). The three ratings per plot were averaged prior to analysis. The center two rows were harvested on 20 Oct using a small plot harvester. The sugar content of the beets was determined by the Amalgamated Sugar Co. laboratory, and the recoverable sugar (lb/A) was estimated. Data were analyzed using the general linear models procedure (Proc GLM-SAS), and Fisher's Protected LSD was used for mean comparisons. Yields were above average and disease pressure was uniform and moderately severe. The commercial hybrids response to Beet curly top virus ranged from acceptable (slight leaf curl to most leaves with moderate curling) to severely affected (most larger leaves becoming prostrate). Analysis of variance indicated there were significant differences among hybrids for diseases index, root yield, sugar content, and estimated recoverable sugar. Our disease ratings positively correlated (r s = 0.913, P < 0.0001) with those from the 04 Curly Top Nursery in Kimberly, ID. Based on Spearman's Coefficient of Rank Correlation (rs = -0.737, P < 0.0001), there was an inverse relationship between estimated recoverable sugar and disease index

Curly top survey in the Western United States

Curly top in sugar beet continues to be a challenging disease to control in the western United States. To aid in development of host resistance and management options, the curtovirus species composition was investigated by sampling 246 commercial fields along with nursery and field trials in the western United States. DNA was isolated from leaf samples and the species were identified using species-specific polymerase chain reaction primers for the C1 gene. Amplicons from 79 isolates were also sequenced to confirm identifications. Beet severe curly top virus (BSCTV) and Beet mild curly top virus (BMCTV) were widely distributed throughout the western United States, while only a few isolates of Beet curly top virus (BCTV) were found. In phylogenetic analysis, BSCTV, BMCTV, and BCTV isolates formed distinct groups in the dendrogram. Seven isolates not amplifiable with species-specific primers did amplify with curly top coat protein primers, indicating novel curtovirus species or strains may be present. Given the wide host range of the viruses responsible for curly top, frequent co-infections, and genetic diversity within and among species, establishing better host resistance, and controlling curly top will continue to be a challenge

Managing curly top

Curly top of sugarbeets caused by Beet curly top virus (BCTV) was widespread from southeastern Oregon to southcentral Idaho in 2004. Curly top first became a serious threat to sugarbeet production in southern Idaho in 1919. By the time the first resistant variety was released in 1935, BCTV had almost eliminated the sugarbeet industry (2). Today this disease is largely managed through the use of resistant varieties. Early planting and the use of systemic insecticides (phorate, aldicarb, and imidicloprid) will also help limit curly top (1,2,4)