2017 ASHS Annual Conference
Laurel Wilt of Avocado: Management of an Unusual and Lethal Disease
Laurel Wilt of Avocado: Management of an Unusual and Lethal Disease
Thursday, September 21, 2017
Kona Ballroom (Hilton Waikoloa Village)
Laurel wilt kills members of the Lauraceae plant family in the southeastern United States, including the important commercial crop, avocado (Persea americana). It is caused by Raffaelea lauricola, a nutritional fungal symbiont of an invasive Asian ambrosia beetle, Xyleborus glabratus, which was detected in Port Wentworth, Georgia in 2002. This invasive insect is the primary vector of R. lauricola in forests along the southeastern coastal plain of the United States, but other ambrosia beetle species that obtained the pathogen after it was introduced in Georgia may play a role in the avocado pathosystem. To date, R. lauricola has been detected in nine additional species of ambrosia beetle, two of which transmitted the pathogen experimentally to avocado and one of which has been shown to reproduce when fed solely on the fungus. Comparisons between R. lauricola and its closest, nonpathogenic relative, R. aguacate, have identified specific genomic attributes that are associated with pathogenicity and which may be useful for disease screening. Sanitation (prompt destruction of affected trees) is needed to successfully manage new outbreaks of laurel wilt, as root-graft transmission of the fungus can result in rapid disease spread and, ultimately, the abandonment of commercial orchards. Early detection of the disease, which is key to successful sanitation, is possible with: 1) frequent scouting for foliar symptoms, 2) remote sensing of spectral reflectance signatures that are associated with the disease, and 3) trained dogs. Although fungicidal protection of avocado trees is possible, it is expensive, requires annual re-treatment and may not be sustainable due to the damage that occurs in treated trees after treatment (fungicide injection). Progress has been made in understanding the vector portion of this puzzle, but reduction of the disease’s impact has not been demonstrated with insecticides, repellents or attractants. Work continues to understand why ambrosia beetle species other than X. glabratus harbor the fungus and what attributes are associated with the alternative vectors. Vascular attributes of different avocado cultivars are associated with laurel wilt susceptibility. For example, highly susceptible West Indian cultivars have significantly higher rates of sapflow, and wider lumen diameters. Current work examines reducing the susceptibility of West Indian cultivars by grafting them onto less susceptible Guatemalan and Mexican genotypes.