Pecan Bacterial Leaf Scorch Disease Review and Update SEPGA, 2013 - - PowerPoint PPT Presentation

Pecan Bacterial Leaf Scorch Disease

Review and Update

SEPGA, 2013

Randy Sanderlin LSU AgCenter Pecan Research-Extension Station Shreveport, LA

Pecan bacterial leaf scorch (PBLS) caused by bacterium Xylella fastidiosa that lives in the water and nutrient conducting tissue of plants it infects

PBLS symptoms begin at edges and near tips of leaflets, tan coloration

Leaflets drop leaving bare leaf stems Repeated annual defoliation can result in dead branches

Effect of PBLS on Yield and Tree Growth

% Reduced Kernel Weight % Reduced Terminal Weight % Leaflet Defoliation Year 1 19 29 67 Year 2 16 32 66 Year 3 14 20 41 Average 16.3 27 58

Effect of PBLS on Early Tree Growth

% Reduced Height % Smaller Diameter 4-year-old trees 40 43 9-year-old trees _ 52

Cultivar Susceptibility To Scorch Disease

Difficult to Categorize –Variation within Individual Cultivars

• Cape Fear
• Cheyenne
• Oconee
• Sumner
• Pawnee
• Desirable
• Forkert
• Moreland
• Elliott
• Stuart
• Candy

Insect Transmission in Pecan

Lateral-lined sharpshooter Johnsongrass sharpshooter Diamond-backed spittlebug Glassy-winged sharpshooter Pecan spittlebug

Photos by: S. Gil Photo by: R. Melanson

• Insect transmission ranged from 2 – 100%

depending on the species of insect

Pecan Spittlebug Adult

Photo by: Rebecca Melanson

Glassy-winged Sharpshooter (GWSS) GWSS about 0.5inch long GWSS feeding on pecan stem

GWSS On Pecan

Observed feeding in large numbers on pecan, prefer succulent growth

Certain plants attract the glassy-winged sharpshooter, including peach, plum, citrus, crepe myrtle

Graft-Transmission of the PBLS Pathogen

• Occurs with infected scions (21%) or rootstocks (85%)
• Can introduce disease into a new orchard
• Manageable:

– Observe potential sources of stocks & scions during late summer for PBLS. – Avoid using diseased trees for graft sources.

• Treat scions with hot water

to eliminate pathogen: 115°F for 30 minutes.

Current Work

• Five subspecies of X. fastidiosa are recognized.

Subspecies are identified by genetic differences and host specialization.

• Rebecca Melanson in her MS work determined that

the strain of XF that infects pecan is subspecies multiplex.

• Recent results suggest that there may be additional

host specialization within multiplex.

Current Objective

• To determine if the pecan strain can infect
• ther hosts of X. fastidiosa.
• Why? Information about pecan strain host

range could be useful in disease management

• X. fastidiosa from pecan is grown in lab culture

Suspension is made from culture and used to inoculate plants by placing suspension drops on main plant stem

Plant absorbs bacterial suspension when needle is passed through drop and into plant

Infection determined by symptoms (two months to a year) and serological test

Pecan X. fastidiosa sp. multiplex Host Range Test

Host Percent of plants Infected by inoculation

2008 2009 2010 2011 Pecan 80 50 85 Plum Sycamore Blueberry

• Red Maple

Grape Oleander

• Pecan may have a limited host range
• Very difficult to establish a negative hypothesis in biology –

always exceptions to the rule

• Additional testing is needed before conclusions can be made

about the host range of pecan XF

• The 2011 and 2012 test plants will be tested with a more

sensitive assay for XF

• Need to determine if XF strains from other plants can infect

pecan

Preliminary Results

Acknowledgements

• Rebecca A. Melanson

– LSU Department of Plant Pathology and Crop Physiology, Baton Rouge, LA

• Stephanie Gil

– LSU Department of Entomology, Baton Rouge, LA

• Mike Hall

– LSU AgCenter Pecan Research-Extension, Shreveport, LA

• Bill Ree

– Texas A&M AgriLife Extension, College Station, TX

• Forrest Mitchell

– Texas A&M AgriLife, Entomology, Stephenville, TX