Sap flow, xylem anatomy and photosynthetic variables of threePerseaspecies in response to laurel wilt

Abstract

Laurel wilt, a lethal vascular wilt disease caused by the fungus Raffaelea lauricola, affects several tree species in the Lauraceae, including three Persea species. The susceptibility to laurel wilt of two forest tree species native to the southern United States, Persea borbonia and Persea palustris, and avocado, Persea americana cv Waldin, was examined and related to tree physiology and xylem anatomy. Net CO2 assimilation (A), stomatal conductance (gs), leaf chlorophyll index (LCI), leaf chlorophyll fluorescence (Fv/Fm), xylem sap flow, theoretical stem hydraulic conductivity (Kh) and xylem vessel anatomy were assessed in trees of each species that were inoculated with R. lauricola and in control trees. Laurel wilt caused a reduction in A, gs, LCI, Fv/Fm, and blockage of xylem vessels by tyloses formation that negatively impacted Kh, and sap flow in all Persea species. However, disease susceptibility as indicated by canopy wilting and sapwood discoloration was less pronounced in P. americana cv Waldin than in the two forest species. Xylem vessel diameter was significantly smaller in P. borbonia and P. palustris than in P. americana cv Waldin. Differences in laurel wilt susceptibility among species appears to be influenced by physiological and anatomical tree responses.

Risk assessment of Hass avocado and Mexican Lauraceae for attack by redbay ambrosia beetle (Coleoptera: Curculionidae: Scolytinae)

“…Upon initial infection, H. lauricola conidia travel through the xylem, triggering the host tree to launch a series of defensive responses, appearing similar to a drought stress response (Castillo‐Argaez, Schaffer, et al, 2020). These defences include secretion of resins and formation of tyloses (outgrowths of parenchymal cells into the xylem vessels) in an attempt to restrict transport of the foreign fungus (Castillo‐Argaez, Vazquez, et al, 2020); however, this response eventually blocks xylem vessels, resulting in systemic wilt and ultimately tree mortality (Inch et al, 2011). Susceptible trees begin to show symptoms within 2 weeks after infection and can die as early as 4 to 6 weeks post‐infection (Hughes et al, 2015a).…”

Different Responses in Vascular Traits between Dutch Elm Hybrids with a Contrasting Tolerance to Dutch Elm Disease

“…As several previous studies suggest, the survival of infected trees appears to be connected with the size of the vessels [ 45 , 46 , 47 ]. An assessment of constitutive traits, such as vessel characteristics before or at the time of infection, is needed and should be supplemented with the study of induced responses in cambial activity and the production of new vessels that were differentiated under specific stimuli.…”

“…Contrary to the genus Ulmus , species of the genus Persea have diffuse-porous wood forming same-sized vessels during the entire growing season. Although the vessels are larger and more prone to become severely invaded by fungi, the remaining vessels may substitute large ones to maintain optimal water transport capacity [ 47 ].…”

Insights into the complexities of fungus‐insect‐plant interaction: The laurel wilt disease

“…Unfortunately, as a consequence of accumulation of tyloses and gums, xylem vessels get blocked and hinder the water conductance that decreases xylem sap flow; this adversely affects leaf gas exchange (Ploetz et al, 2015). Castillo-Argaez et al (2021) found that, in three species of Persea sp., about 50% of xylem vessels were clogged by tyloses accumulation as a result of laurel wilt infection. Also, in the same study, they observed different symptoms like branch dieback, leaf wilting, and discoloration of sapwood which attributed to the embolisms, and were also the consequence of tyloses blockage.…”

“…Castillo‐Argaez et al. (2021) found that, in three species of Persea sp., about 50% of xylem vessels were clogged by tyloses accumulation as a result of laurel wilt infection. Also, in the same study, they observed different symptoms like branch dieback, leaf wilting, and discoloration of sapwood which attributed to the embolisms, and were also the consequence of tyloses blockage.…”