Pecan Bacterial Leaf Scorch Disease Review and Update

Transcription

1 Pecan Bacterial Leaf Scorch Disease Review and Update SEPGA, 2013 Randy Sanderlin LSU AgCenter Pecan Research-Extension Station Shreveport, LA

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

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

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

5 Effect of PBLS on Yield and Tree Growth % Reduced Kernel Weight % Reduced Terminal Weight % Leaflet Defoliation Year Year Year Average

6 Effect of PBLS on Early Tree Growth 4-year-old trees 9-year-old trees % Reduced Height % Smaller Diameter _ 52

7 Cultivar Susceptibility To Scorch Disease Difficult to Categorize Variation within Individual Cultivars Cape Fear Cheyenne Oconee Sumner Pawnee Desirable Forkert Moreland Elliott Stuart Candy

8 Insect Transmission in Pecan Insect transmission ranged from 2 100% depending on the species of insect Pecan spittlebug Lateral-lined sharpshooter Johnsongrass sharpshooter Diamond-backed spittlebug Glassy-winged sharpshooter Photo by: R. Melanson Photos by: S. Gil

9 Pecan Spittlebug Adult Glassy-winged Sharpshooter (GWSS) Photo by: Rebecca Melanson GWSS about 0.5inch long GWSS feeding on pecan stem

10 Observed feeding in large numbers on pecan, prefer succulent growth GWSS On Pecan

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

12 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.

13 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.

14 Current Objective To determine if the pecan strain can infect other hosts of X. fastidiosa. Why? Information about pecan strain host range could be useful in disease management

15 X. fastidiosa from pecan is grown in lab culture

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

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

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

19 Pecan X. fastidiosa sp. multiplex Host Range Test Host Percent of plants Infected by inoculation Pecan Plum Sycamore Blueberry Red Maple Grape Oleander

20 Preliminary Results 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

21 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