Progress 07/01/05 to 06/30/10
Outputs
CONTINUED DETECTION OF A NEW PATHOTYPE OF BEET NECROTIC YELLOW VEIN VIRUS (BNYVV). A resistance-breaking pathovar of BNYVV, the cause of rhizomania, was detected by enzyme-linked immunosorbent assay (ELISA) in root tissue from resistant sugarbeets containing the Rz1 resistance gene. In 2007, soil samples were collected from fields in southern Idaho where resistant varieties were showing symptoms of rhizomania. Bioassays were conducted using a set of four differential test varieties with rz, Rz1, Rz2 and Rz1+Rz2 genes. Soil samples were mixed 1:1 with sterile sand. After 5 weeks of growth in controlled environment at 26.7 C and 12 hr light, plants were harvested and 0.5g subsamples of washed roots were analyzed with ELISA. A sample was considered positive for BNYVV if the test value is greater than or equal to 3.00x the healthy check value. The variability in positive reactions to the test varieties suggests that as many as six different resistance-breaking pathovars of
BNYVV may be present. Eight classes and presentations were given to growers, fieldmen, and sugarbeet seed company breeders throughout Idaho during 2007 informing them of the resistance-breaking pathovars of BNYVV and providing management techniques. Growers are also advised to monitor irrigation to prevent the excess soil moisture required for rhizomania development. Cooperated with USDA in a project assessing the storability of sugarbeets infected with Beet Necrotic Yellow Vein Virus.
Impacts
All rhizomania-resistant sugarbeet varieties grown in the U.S. carry only the Rz1 resistance gene. Nearly all fields where new pathovars have been detected since have also been intensively cropped to rhizomania-resistant sugarbeet varieties with shorter rotations than recommended. Resistance-breaking pathovars of BNYVV are likely being selected from the pathogen population in such fields. Growers are advised to lengthen the rotation to at least four years. Lengthening the rotation can reduce the selection pressure on the pathogen and add additional time before new pathovars develop high enough populations to cause loss. This may allow USDA and private breeding programs the additional time needed to develop varieties resistant or tolerant to the new pathovars.
Publications
- Strausbaugh, C.A., Rearick, E., Camp, S., Gallian, J.J. and Dyer, A.T. 2008. Influence of Beet necrotic yellow vein virus on Sugar Beet Storability. Plant Dis. 92: accepted for publication on 7 November 2007.
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Progress 01/01/06 to 12/31/06
Outputs
CONTINUED DETECTION OF A NEW PATHOTYPE OF BEET NECROTIC YELLOW VEIN VIRUS (BNYVV). A resistance-breaking pathovar of BNYVV, the cause of rhizomania, was detected by enzyme-linked immunosorbent assay (ELISA) in root tissue from resistant sugarbeets containing the Rz1 resistance gene. In 2006, 18 soil samples were collected from 17 fields in southern Idaho in 2006 where resistant varieties were showing symptoms of rhizomania. Two samples were taken from one field where two resistant varieties were displaying differing symptoms. All except one bioassay were conducted using a set of four differential test varieties with rz, Rz1, Rz2 and Rz1+Rz2 genes. In one bioassay only the Rz1+Rz2 gene test variety was used. Each soil sample was mixed 1:1 with sterile sand and two pots were planted of each test variety. After 5 weeks of growth in controlled environment at 26.7 C and 12 hr light, plants were harvested and 0.5g subsamples of washed roots were analyzed with ELISA. A
sample was considered positive for BNYVV if the test value is greater than or equal to 3.00x the healthy check value. All bioassays tested with the rz (susceptible) test variety except one were positive for BNYVV. Of the 18 samples, 16 tested positive with at least one of the resistant test varieties, indicating the presence of a resistance-breaking pathovar of BNYVV in 88.6 percent of the samples, compared with 56.3 percent of 16 samples in 2005. In 2006, 55.6 percent of the samples tested positive with all four test varieties, while none of the samples did in 2005. The variability in positive reactions to the test varieties in 2006 suggests that as many as six different resistance-breaking pathovars of BNYVV may be present.
Impacts
All rhizomania-resistant sugarbeet varieties grown in the U.S. carry only the Rz1 resistance gene. Nearly all fields where new pathovars have been detected have also been intensively cropped to rhizomania-resistant sugarbeet varieties with shorter rotations than recommended. Resistance-breaking pathovars of BNYVV are likely being selected from the pathogen population in such fields. Growers are advised to lengthen the rotation to at least four years. Lengthening the rotation can reduce the selection pressure on the pathogen and add additional time before new pathovars develop high enough populations to cause loss. This may allow USDA and private breeding programs the additional time needed to develop varieties resistant or tolerant to the new pathovars.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
OCCURRENCE OF A NEW PATHOTYPE OF BEET NECROTIC YELLOW VEIN VIRUS (BNYVV). A resistance-breaking pathovar of BNYVV, the cause of rhizomania, was detected by enzyme-linked immunosorbent assay (ELISA) in root tissue from resistant sugarbeets containing the Rz1 resistance gene. Soil was collected in 2004 from 11 suspect fields where resistant varieties were showing rhizomania symptoms. A bioassay was conducted using a set of four differential varieties with rz, Rz1, Rz2 and Rz1+Rz2 genes. All bioassays were positive for BNYVV against the rz (susceptible) test variety, and seven of the 11 bioassays tested positive against the Rz1. Five bioassays were positive against the rz, Rz1 and Rz2 test varieties, and three were positive against all test varieties. Similar bioassays were conducted in soils collected in 2005 from 16 fields. Nine of the 16 fields tested positive for BNYVV resistance-breaking isolate(s). The variability in positive reactions to the test varieties
suggests that as many as five different pathovars of the BNYVV may be present. RHIZOMANIA VARIETY TESTS. In 2005, commercial and experimental rhizomania-resistant varieties adapted to the Idaho growing area were tested in Twin Falls, Idaho, in a field that had been inoculated in 2000 with rhizomania-infested soil and susceptible sugarbeets grown to establish disease. Two separate tests were conducted with standard rhizomania-resistant varieties in one test and transgenic Roundup-Ready rhizomania-resistant varieties in the other. In the standard rhizomania test there were 50 entries plus two rhizomania-susceptible check varieties. In the transgenic Roundup-Ready rhizomania test there were seven entries plus two check varieties, one rhizomania-resistant and one rhizomania-susceptible. Disease was uniform and moderate throughout both tests in the susceptible checks. Average root yield and average recoverable sugar of the three highest performing varieties in the standard rhizomania test
was 13.88 tons/A and 4484 lb/A higher, respectively, than the susceptible check varieties. In the transgenic test, average root yield of the three highest test varieties was 13.22 tons/A higher than the susceptible check variety, and 4101 lb/A higher in estimated recoverable sugar. Disease index (DI) of susceptible check varieties was significantly higher than all varieties in the Roundup-Ready test and all except two resistant varieties in the standard test. All varieties were evaluated for resistance to curly top virus in a nursery operated by the Beet Sugar Development Foundation, and all data were provided to a grower committee for their determination of varieties to be approved for planting in the Idaho, Oregon and Washington growing area. GREEN MANURE FOR RHIZOMANIA MANAGEMENT. Oilseed radish (Raphanus sativus) that has been used as a trap crop for sugarbeet cyst nematode (Heterodera schachtii) was tested as a green manure for rhizomania management. In contrast to previous years
results, there were no differences in field performance of sugarbeets following the green manure compared with the untreated checks.
Impacts
All rhizomania-resistant sugarbeet varieties grown in the U.S. carry only the Rz1 resistance gene. Most fields where new pathovars have been detected have been intensively cropped to rhizomania-resistant sugarbeet varieties with shorter rotations than recommended. Resistance-breaking pathovars of BNYVV are probably being selected from the pathogen population in such fields. Growers are advised to lengthen the rotation to at least four years, and most are complying. Lengthening the rotation can reduce the selection pressure on the pathogen and add additional time before new pathovars develop high enough populations to cause economic loss. This may allow USDA and private breeding programs the additional time needed to develop varieties resistant or tolerant to the new pathovars. Variety test information gives growers accurate information for variety selection.
Publications
- Gallian, J.J. and Vargas, D. 2005. The University of Idaho sugarbeet rhizomania variety performance tests, 2004. Proc. Univ. Idaho Winter Commodity Schools 37:197-200.
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