Survey to Determine the Occurrence of Xylella Fastidiosa and its ...

Survey to Determine the Occurrence of
Xylella Fastidiosa and its vector,
GWSS, in selected Alabama Orchards
Dr. Elina Coneva
Department of Horticulture, Auburn University

Acknowledgements
M.S. Candidate Xing Ma
Dr. John Murphy
Dr. Henry Fadamiro
ACES:
Bobby Boozer
Jim Pitts
Larry Wells
Grower Co-operators:
Ken Buck
Allan Norden
Jimmy Witt
John Neighbors
Bob Helms
Wes Isom

What is Xylella fastidiosa
Xylem-limited Bacterium
Xylella fastidiosa in infected plum tree
(Latham and Norton, 1980)
X. f. bacteria in the water-conducting cells
(xylem) of a grape leaf vein

How X.f. Bacterium Affects the Plant
‣ Moves in plant xylem systematically
‣ Multiplies
‣ Accumulates
‣ Form a bioflim in the susceptible hosts
‣ Plug the xylem vessel of the plant

Disease Significance
‣ Plant diseases caused by Xylella fastidiosa have
emerged as some of the most significant new disease
threats in Americas
‣ X. f. has a wide range of hosts
‣ Introduction of new strains of X. f. resulted in new
host-pathogen combinations - Citrus Variegated
Chlorosis (1980s)
‣ There is no known cure

FRUIT CROP HOSTS
‣ Bunch grapes - Pierce’s Disease (PD) in and contributed
to the outbreak of PD in CA vineyards in the 1990s
‣ Plums - Plum leaf scald - one of the most serious
diseases limiting the production of plums in AL (Latham
and Norton, 1980)
‣ Peaches - Phony peach occurs in the Coastal Plain
from NC to Texas
‣ Citrus – Citrus Variegated Chlorosis (CVC) found in
Brazil in 1987; 2 million citrus trees affected 5 yrs later
‣ Blueberry - Blueberry leaf scorch found in GA in 2006

SYMPTOMS ON GRAPE
• Leaf necrosis
• Dieback
• “Match stick”

SYMPTOMS ON PLUM
‣ Leaf marginal
necrosis
‣ Death of entire
branches

SYMPTOMS ON PEACH
‣ Stunted growth
‣ Dark green canopy
‣ Flat top
‣ Small fruit

SYMPTOMS ON CITRUS
Small infected fruit
compared with
normal fruit
Leaf interveinal chlorosis

SYMPTOMS ON BLUEBERRY
Marginal leaf burn
and scorch
Yellow stems after
leaf abscision
Similar to anthracnose
leaf spot

Disease Transmission
‣ Pruning tools
‣ Stock to scion
‣ Vectors: Xylem-feeding
leafhoppers

Glassy-Winged Sharpshooters (GWSS)
‣ 28 species are confirmed vectors
‣ Strong flyer
‣ Feed on different plant
‣ Feeding on woody part of grapes

OBJECTIVES
‣ Survey the presence and occurrence of Xylella
fastidiosa in commercially important fruit crops in
Alabama
‣ Identify the vector species and estimate the
seasonal dynamics of glassy-winged sharpshooter in
selected AL locations

Site Selection for
Plant Tissue Sampling
‣ 21 orchards sampled 3 X
‣ Fruit Crops:
- Peach
-Plum
- Satsuma mandarin
- Bunch grapes
- Muscadines

Insect Sampling
Three locations were selected
to determine the insect
- identity;
- abundance;
- seasonal dynamics

‣ Four yellow sticky traps per crop
‣ Collected on bi-weekly intervals April - October

RESULTS
‣ Less than 1% peach and plum samples infected
‣ 50% of bunch grapes infected

%
50
10
100

100%
80%

Glassy-Winged Sharpshooter Species
Homalodisca vitripennis Homalodisca insolita Oncometopia orbona

Average Number of GWSS in Three AL Locations, 2008
Gulf Coast
Central AL
North AL
‣ Gulf Coast – highest number, end of June peak
‣ Central AL – low insect pressure, end of July peak
‣ North AL – very low insect pressure

Average Number of GWSS Among Fruit Crops in the Gulf Coast of AL, 2008
Plum - 230
Muscadine - 170
Satsuma - 55
Peach - 37

SUMMARY
‣ X. f. infected peach and plum orchards throughout the state
and infected bunch grapes in Central and North AL
‣ X. f. positive results from asymptomatic trees found on
plum, peach, and bunch grape
‣ Three GWSS species were prevalent in AL orchards
‣ Gulf Coast had the highest incidence of GWSS
‣ Maximum insect pressure in mid June on plum
‣ The peak incidence of GWSS in Central AL occurred 40
days after the peak in the Gulf Coast
‣ The insect incidence in North AL was very low

THANK YOU!