funky leaf spot, viruses, and xylella update – winter...
TRANSCRIPT
Funky Leaf Spot, Viruses, and Xylella Update – Winter 2011
Phillip M. Brannen
University of Georgia Plant Pathology Department
Background: Systemic Blueberry Diseases
� At least nine species of plant viruses infect blueberries in North America
� Some (such as scorch and shock viruses) are very damaging, whereas most others are highly variable in level of damage
� Historically, southern blueberries have been essentially virus-free– 2000: a few plants positive for Blueberry shoestring virus or
Strawberry latent ringspot virus in south GA– 2001: no positives in sample of 93 suspects in large NC & GA
virus survey– Since 2005: increased prevalence and severity of viral and
virus-like diseases on southern highbush
Blueberry red ringspot virus (BRRV)Fall Spring
Blueberry red ringspot virus (BRRV)
BRRV on Ozarkblue fruit in NC (courtesy Bill Cline, NCSU)
� Mosaic, mottling, ringspotting� Foliar symptoms most
pronounced in fall (absent in spring)
� Stem symptoms most pronounced in spring
� Fruit symptoms not seen in GA� No known in-field vector, most
likely transmitted via cuttings� Effects on plant growth and yield
poorly documented
Prevalence of Blueberry red ringspot virus (BRRV) and necrotic ringspot disease in different counties in Georgia, based on a survey conducted in fall of 2008.
Scherm et al., 2008
Scherm et al., 2008
Prevalence of Blueberry red ringspot virus (BRRV) and necrotic ringspot disease on different southern highbush cultivars in Georgia, based on a survey conducted in fall of 2008.
Phil Harmon (Univ. of Florida) did observe transmission of the disease in a greenhouse. Infected plants on one table, collected for experimentation, were placed opposite non-infected plants. Within two months, most of the non-infected plants were showing the disease symptoms. Mites were found in association with the diseased plants, but data is preliminary at best.
Blueberry Shock
�Spread through propagation or pollen (bees). � In theory, the bees coming from Michigan to
Georgia should not be a problem, since the pollen would not be active when the bees come to Georgia (pollen too old).
� 1-2 year latent period before symptoms.�Plants eventually recover, but losses are severe
for several years.
Blueberry Scorch
�Spread through propagation or aphids. � 1-2 year latent period before symptoms.�Plants eventually die, and losses are significant
until death occurs.
Temecula isolate (WT))
Xylella fastidiosa
A small, fastidious, Gram negative, xylem-inhabiting bacterium related to Xanthomonas spp.
Tissue specific, confined to tracheary elements, tracheids or vessels
Photo by H.C. Hoch, Cornell University; Journal of Bacteriology.
189:7507–7510.
XF1968F3/XF1968R3 Primer Results
1 kb BB21 BB1 BB9 G11 Teme OL2 T1B T5C Dixon M12 FL GA NegLadder Oak Plum Ctrl
Several strains of X. fastidiosa courtesy of Dr. Jianchi Chen, USDA-ARS, Parlier, CA
Blueberry Grape Oleander Almond
Results from multiple primers indicate the blueberry X. fastidiosa is not piercei
L. Nissen and T. Denny
Blueberry survey locations with confirmed Xylella fastidiosa infections. Plants symptomatic for bacterial leaf scorch were confirmed through ELISA (map developed using Google Earth).
Incidence (percentage of symptomatic plants) of bacterial leaf scorch by cultivar at one 7th leaf producer site in Colquitt County. The number of rows surveyed (n) is shown in parentheses next to the cultivar name.
FL 86-19 [V1]
Emerald
Millennium
Windsor
Southern Belle
FL 86-19 (V1) y = 7.7299x - 1.7131R2 = 0.4022F = 0.002
0
20
40
60
80
100
0 2 4 6 8 10 12
Years
Dis
ease i
ncid
en
ce (
%)
Star y = 3.2974x - 4.2256R2 = 0.2758F = 0.00004
0
20
40
60
80
100
0 2 4 6 8 10 12
Years
Dis
ea
se
in
cid
en
ce
(%
)
Disease incidence (percentage of symptomatic plants) of bacterial leaf scorch observed on cultivars FL 86-19 (V1) and Star over time (years in the field). Both cultivars are susceptible to the disease, but FL 86-19 is clearly more susceptible to disease development and spread than Star. Based on the trend lines projected through use of survey data, ~75% of FL 86-19 plants would be symptomatic by the tenth year in the field, versus ~30% in Star.
Can we screen for resistance in the greenhouse to obtain rapid evaluations of blueberry lines?
Blueberry leaf scorch symptom Development with 10-fold dilution of 0.25 OD BB08-2 Inoculum (2009)
0
1
2
3
4
6wk
8wk
10wk
12wk
14wk
16wk
18wk
V1StarWindsorEmerald
Blueberry leaf scorch symptom development with 0.25 OD BB08-3 inoculum (2010 test)
0
1
2
3
4
2 mo 3 mo 4 mo 5mo
V1StarWindsorEmerald
Blueberry leaf scorch symptom development with 0.25 OD BB08-3 inoculum (2010 test)
0
1
2
3
4
2 mo 3 mo 4 mo 5 mo
V1ClimaxSouthern BelleTif BlueRebel
Cultivar Field GreenhouseV1 Susceptible SusceptibleStar Susceptible Moderate Res.Windsor Resistant ResistantEmerald Resistant SusceptibleRebel Susceptible SusceptibleSouthern Belle Resistant ResistantClimax ? ResistantTif Blue ? Resistant
Comparison of Field Resistance to Blueberry Leaf Scorch and Greenhouse Resistance
0
0.5
1
1.5
2
2.5
3
Leaf
sco
rch
ratin
g
Four months after Inoculation
BB08-3 EB06-1SCBB08-1 B1-10 GAB2-64 GA B2-66 GABuffer
Pathogenicity of Xylella fastidiosa strains to Emerald, 2010 test
Greenhouse Screening for Resistance to Leaf Scorch
� Resistance to blueberry leaf scorch in greenhouse screening agreed with observed field resistance for most cultivars.
� Emerald was more susceptible to Xylella fastidiosa in the greenhouse than in the field.
� Star appeared to be more resistant in greenhouse tests than has been observed in the field.
� Differences between greenhouse and field observations could be due to host specificity of strains, aggressiveness of strains, or loss of virulence in some strains during culture.
Evaluation of Benign Strains of X. fastidiosa for the Biological Control of Blueberry Leaf Scorch by Cross-Protection
� Various strains of X. fastidiosa are being evaluated in the greenhouse for biological control of blueberry leaf scorch in ‘Star’ and ‘V1’, including strains from elderberry, blackberry, sycamore, and mulberry.
� ‘Star’ and ‘V1’ blueberry plants inoculated with these strains were challenged 3-4 weeks later with the blueberry leaf scorch strain BB08-2 in 2009 or BB08-3 in 2010 to evaluate biological control of the disease.
� Disease incidence and severity are rated once a month.
Don Hopkins, UF
0
1
2
3Le
af s
corc
h ra
ting
Five months after Inoculation with BB08-3
Buffer EB92-1
Syc86-1 BKB95-1
Dixon PD00-2
Biological Control of Blueberry Leaf Scorch in V1 (2010 test)
Biocontrol of Blueberry Leaf Scorch
� In greenhouse tests, X. fastidiosa strains EB92-1 and Syc86-1 reduced leaf scorch in both Star and V1. BKB95-1 provided biocontrol in Star and PD00-2 was effective in V1.
� Strain PD00-2 is not a candidate for biocontrol of blueberry leaf scorch, because it is pathogenic to grapevine.
� Further greenhouse and field tests are warranted for EB92-1, Syc86-1, and possibly BKB95-1.
Summary � In addition to X. fastidiosa strains from blueberry, strains
from lupine, almond, and elderberry were pathogenic to blueberry.
� Resistance to blueberry leaf scorch in greenhouse screening agreed with observed field resistance for most cultivars. The development of a quick screening test for resistance to leaf scorch is possible.
� Differences in virulence or host specificity were observed in X. fastidiosa strains used in greenhouse tests.
� Greenhouse tests for the biological control of leaf scorch were positive. Field tests are needed.
Vectors of Xylella species diseases are limited to sharpshooter and spittlebug insects, of which the glassy-winged sharpshooter (Homalodisca vitripennis) is primary in the Southeast.
University of California
Homalodisca insolita Paraulacizes irrorata
Credits: Susan Ellis
Draeculacephala sppOncometopia nigricans
0.25% 0.77% 0.25% 1%
Graphocephala versuta 0.51%
Emphasis on glassy-winged sharpshooter (Homalodisca vitipennis), which constituted 97% of leafhoppers sampled within bushes season-long at two field sites 97%
Credit: University of California
Dr. Moukaram Tertuliano, 2009
Feeding preference of glassy-winged sharpshooter in choice test
� Total of 4 plants (reps) per cultivar tested sequentially
� For each rep, 20 leafhoppers released in cage containing one plant per cultivar
� Five days observation, plant position rotated every day
� Number of leafhoppers settled/feeding per plant recorded daily
Emerald
Star
V155%
27%
17%
GWSS feeding on blueberry cultivar
Early plant growth (3 months after transplanting) was reduced for BRRV and Xylella cuttings, although Xylella cuttings were still asymptomatic at that time. In fall 2010, 15 months after transplanting, 100, 8.9 and 0% of plants derived from the summer 2009 BRRV, Xylella, and funky spot cuttings, respectively, showed visual disease symptoms.
Scherm et al., 2010