Sugar
Beet Polymyxa-Vectored Viruses
Beet necrotic yellow vein virus (BNYVV) and
Beet soil borne mosaic virus (BSBMV) are closely
related viruses found throughout the growing regions
of Minnesota and North Dakota. BNYVV is the casual
agent of rhizomania and results in a severe reduction
of extractable sucrose and yield. Both viruses are
vectored by the same fungus, Polymyxa beta,
and occupy similar ecological niches. This has raised
concern about virus recombination because none of
the US germplasm is resistant to BSBMV. Most commercial
beet varieties are resistant to BNYVV (most carry
the Holly gene), however with the increase in acres
planted to beet varieties resistant to BNYVV, the
possibility of selection for new more resistant strains
of this virus has increased. In 2002, a strain of
BNYVV was found in California’s Imperial Valley
on a beet variety that should have been resistant
to BNYVV. USDA in Salinas CA confirmed virulence of
this isolate on resistant sugar beets, putting nearly
all of the US germplasm at risk. By understanding
the variability that exists in natural populations
of these viruses, we can evaluate the risk to sugar
beet growers.
Objective 1. Quantify intraspecific genotypic
variation among isolates of BNYVV and BSBMV.
We have found deletions in the read-through protein
(75 KDa) of BSBMV ranging in size from 363 bp to 460
bp. The 75 KDa read-through protein is one of the six
open reading frames (ORF’s) of BSBMV and BNYVV
RNA2. It is a complex which contains the coat protein
and 495 additional amino acids, and results from the
translational suppression of the coat protein termination
codon. It has been shown to be essential for transmission
of BNYVV virus by Polymyxa betae. Deletions in
isolates from North Dakota, Colorado, and Texas removed
a significant part of the read-through gene, but do
not appear to have any effect on serological detection
or transmission by the fungus Polymyxa betae.
Similar studies with both BSBMV and BNYVV continue.
Objective
2. Relate virus genotype to incidence and severity of
infection in resistant and susceptible sugar beet cultivars.
In studies of soil from BNYVV resistance trials in the
American Crystal and Southern Minnesota regions, we
have found that variety trials Beta 4818, HM 2411, Crystal
999, and HM 7169 contained the major percentage of BNYVV
infection. There was a high percentage of BSBMV recovered
from most of the cultivars with no BNYVV infection and
a few cultivars were infected with both viruses. It
would be interesting to elucidate the epidemiological
relationship between the two viruses.
Objective
3. Measure disease tolerance among BNYVV tolerance cultivars
by quantitative PCR.
In order to determine whether sugar beet cultivars perform
well as a result of genetic resistance or regional adaptability,
fluorescent real-time PCR will be used to quantify viral
titer in susceptible and disease tolerant cultivars.
Susceptible and resistant beet cultivars will be infested
with BNYVV and ELISA analysis will be performed to determine
viral infection. RNA extracted from the infected roots
will be analyzed by fluorescent real-time PCR to quantify
viral titer in the roots of the sugar beet seedlings.
Quantitative results of viral tolerance will be obtained.
Objective
4. Examining the spatial distribution in a field.
Other related websites:
Description
of Plant Viruses Website
