Laurel Wilt in Natural and Agricultural Ecosystems: Understanding the Drivers and Scales of Complex Pathosystems

Abstract

Laurel wilt kills members of the Lauraceae plant family in the southeastern United States. It is caused by Raffaelea lauricola T.C. Harr., Fraedrich and Aghayeva, a nutritional fungal symbiont of an invasive Asian ambrosia beetle, Xyleborus glabratus Eichhoff, which was detected in Port Wentworth, Georgia, in 2002. The beetle 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 the initial introduction may play a role in the avocado (Persea americana Miller) pathosystem. Susceptible taxa are naïve (new-encounter) hosts that originated outside Asia. In the southeastern United States, over 300 million trees of redbay (P. borbonia (L.) Spreng.) have been lost, and other North American endemics, non-Asian ornamentals and avocado-an important crop that originated in MesoAmerica-are also affected. However, there are no reports of laurel wilt on the significant number of lauraceous endemics that occur in the Asian homeland of R. lauricola and X. glabratus; coevolved resistance to the disease in the region has been hypothesized. The rapid spread of laurel wilt in the United States is due to an efficient vector, X. glabratus, and the movement of wood infested with the insect and pathogen. These factors, the absence of fully resistant genotypes, and the paucity of effective control measures severely constrain the disease's management in forest ecosystems and avocado production areas.

Host density dependence and environmental factors affecting laurel wilt invasion

“…R. lauricola populations are quite diverse in East Asia, but the pathogen and its vector seem to be clonal in the US (Cognato et al 2019;Dreaden et al 2019;Hughes et al 2017;Wuest et al 2017). This suggests that both were introduced in a single event, possibly being carried to the port of entry in untreated packing material Ploetz et al 2017). Since the introduction of X. glabratus and R. lauricola in the US, the disease has spread to 198 counties in nine states in the Southeastern US (USDA Forest Service 2019).…”

“…To date, an estimated 300 million redbay trees have been killed by laurel wilt , roughly a third of the original native population. Other plants in the Lauraceae, such as the endangered pondberry (Lindera melissifolia) and gulf licaria (Licaria trianda), are threatened with extinction, with unknown environmental consequences Ploetz et al 2017). In addition, commercial production of avocado, P. americana Miller, is affected in Southern Florida and threatened elsewhere Ploetz et al 2013).…”

“…Subsequently, we evaluated laurel wilt disease dynamics at another site in South-central Florida for which detailed spatio-temporal information over the course of an epidemic was available. Previous studies of laurel wilt have focused on redbay and avocado (Hanula and Sullivan 2008;Hughes et al 2017;Ploetz et al 2017;Shields et al 2011). In the present work, in addition to redbay, we studied swampbay P. palustris, syn.…”

Variability and Disturbances as Key Factors in Forest Pathology and Plant Health Studies

“…In the case of cypress canker, the use of the artificially created hybrid Leyland cypress has significantly increased the severity of outbreaks, even where the causal agent is native (e.g., in California) [22]. In the case of laurel wilt, the high susceptibility of cultivated avocados has accelerated the spread of the disease in natural ecosystems [23]. On top of this, and unfortunately, the exotic laurel wilt pathogen, introduced in conjunction with the introduction of an exotic ambrosia beetle, has been picked up by multiple native beetles, thus immediately broadening its host range.…”

Laurel Wilt Disease: Early Detection through Canine Olfaction and "Omics" Insights into Disease Progression

“…Since spreading to S Florida in 2012, it has posed and continues to pose a significant and growing threat to the avocado industry . (The reader is directed to a thorough review on the current status, goals and challenges involved with management and control of this disease by Ploetz et al (2017)). …”