Symbiosis between beetles and fungi arose multiple times during the evolution of both organisms. Some of the most biologically diverse and economically important are mutualisms in which the beetles cultivate and feed on fungi. Among these are bark beetles and Harringtonia, a fungal genus that produces Raffaelea-like asexual morph and hosts the causal agent of laurel wilt, H. lauricola (formerly Raffaelea lauricola). In this study, we propose four new species of Harringtonia associated with beetles from Belize and Florida (USA). We hope to contribute towards a more robust and inclusive phylogenetic framework for future studies on these beetle-fungi relationships and their potential impact in crops and forests worldwide.

The accumulation of salt deposits in the soil is becoming a major problem in agriculture. The problem can affect citrus production, which is already seriously hindered in Florida by the disease known as Huanglongbing (HLB, or citrus greening). With the citrus industry declining, it is imperative to study all potential environmental stresses affecting the citrus cultivation and to conduct screening tests to evaluate which rootstocks perform best under these challenging new conditions. This study aims to determine how the ‘US-942’ rootstock reacts to salinity. Thirty-six 3-month-old ‘US-942’ citrus rootstock seedlings were grown in a greenhouse. After 15 d of acclimation, plants were assigned to one of six groups and treated for 30 d with solutions of 25% Hoagland solution amended with 0 (control), 30, 60, 90, 120, or 150 mm NaCl. Higher NaCl concentrations significantly hindered plant growth and negatively affected some physiological processes [i.e., stomatal conductance (gS)] and chlorophyll contents. Conversely, plants treated with mild concentrations (30 mm NaCl) had higher plant biomass and exhibited higher photosynthetic efficiency. Free hand sections of fresh roots were taken at the end of the experiment, and the suberin lamellae development was examined under a fluorescence microscope. In conclusion, results reported that ‘US-942’ rootstock is tolerant to mild salt stress and confirmed the hypothesis that the formation of root apoplastic barriers and the increase in the root biomass could be two possible mechanisms that give the ‘US-942’ a mild NaCl stress tolerance.

Background. Ambrosia beetles include well-known invasive pests, but most species established in non-native areas do not cause any significant impact. Here we report the recent invasion and rapid spread of Ambrosiodmus minor in the Southeastern US. Methods: We used a combination of a multi-year survey, literature data on fungal symbionts from the beetle mycangia and in vitro bioassays of fungal competition, and extensive field observations of wood colonization patterns. Results. In less than seven years, A. minor abundance has increased many-fold in Florida. The beetle is associated with an aggressive wood-rot fungus Flavodon ambrosius. Joint colonization of wood by A. minor and F. ambrosius results in extensive white rot (lignin removal). The invasion of this symbiosis may impact an ecosystem function previously considered not influenced by non-native ambrosia beetles: wood decay. We suggest monitoring of the impact of this invasion on native wood-inhabiting organisms, biomass degradation and the carbon cycle throughout the region.

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Ambrosia beetles in the subtribe Hyorrhynchini are one example of an entire ambrosia beetle lineage whose fungi have never been studied. Here, we identify one dominant fungus associated with a widespread Asian hyorrhynchine beetle Sueus niisimai. This fungus was consistently isolated from beetle galleries from multiple collections. Phylogenetic analyses of combined ITS rDNA and β-tubulin sequences identified the primary fungal symbiont as Diatrypella japonica Higuchi, Nikaido & Hattori (Diatrypaceae, Xylariales, Sordariomycetes), which was recently described as a pathogen of sycamore (Platanus spp.) in Japan. To assess the invasion potential of this beetle-fungus interaction into the US, we have investigated the pathogenicity of two Diatrypella japonica strains on four species of healthy landscape trees native to the southeastern United States. Only Shumard oak (Quercus shumardii) responded with lesions significantly greater than the control inoculations, but there was no observable dieback or tree mortality. Although disease symptoms were not as prominent as in previous studies of the same fungus in Japan, routine re-isolation from the inoculation point suggests that this species is capable of colonizing healthy sapwood of several tree species. Our study shows that the geographical area of its distribution is broader in Asia and potentially includes many hosts of its polyphagous vector. We conclude that the Sueus-Diatrypella symbiosis has high invasion potential but low damage potential, at least on young trees during the growing season.