Further pathogenicity testing of Verticillium nonalfalfae, a biocontrol agent against the invasive Tree of Heaven (Ailanthus altissima), on non-target tree species in Europe.

Verticillium nonalfalfae is an effective biological control agent against the highly invasive Tree of Heaven (Ailanthus altissima) in Europe, and previous research on ten economically and ecologically important tree species occurring in Austria have so far not revealed undesired non-target effects. In this study, another nine tree species including five native, two non-native as well as two invasive alien tree species were tested for susceptibility to the particular strain of V. nonalfalfae (Vert56) used for biological control of A. altissima. Stem inoculations on potted seedlings revealed that this strain of V. nonalfalfae is generally host-adapted to A. altissima. It induced chlorosis, necrosis and wilting already within two weeks post inoculation on A. altissima and resulted in almost completely defoliated or dead seedlings at the end of the vegetation period. Apart from two species (Quercus rubra and Sorbus aucuparia), that suffered from other abiotic/biotic agents, no mortality was observed on all other tree species tested; however, symptoms caused by other abiotic factors were also found on Prunus avium and Ulmus glabra. All tested tree species exhibited vascular discolorations and the fungus could be re-isolated at varying frequencies (6-100%) from inoculated seedlings of all non-target tree species, although five of these species exhibited no external symptoms. Results confirmed high susceptibility (S) of A. altissima to V. nonalfalfae, whereas Acer platanoides, Castanea sativa, Q. rubra, S. aucuparia and U. glabra were considered as tolerant (T), and A. negundo, P. avium, P. serotina and Q. petraea were rated as possible resistant (PR) due to the low rates of re-isolation. Supplementary Information: The online version contains supplementary material available at 10.1007/s12600-022-01032-z.

Application of elemental bioimaging using laser ablation ICP-MS in forest pathology: distribution of elements in the bark of Picea sitchensis following wounding.

Element distribution in the bark of two 20-year-old clones of Picea sitchensis following wounding was studied using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Bark was sampled at 0, 3, and 43 days after wounding and analysed using a focused Nd:YAG laser (266 nm). Intensities of (13)C, (25)Mg, (27)Al, (31)P, (32)S, (39)K, (48)Ca, (55)Mn, (57)Fe, (63)Cu and (64)Zn were measured by ICP-MS to study elemental distribution across the bark samples during the wound repair process. A clear accumulation of Mg, P and K at the boundary zone between the lesion and healthy tissue was detected in the wounded samples and was more distinctive at 43 than at 3 days after treatment. This zone of accumulation mapped onto the position of formation of the ligno-suberised boundary zone and differentiation of the wound periderm. These accumulations suggest major roles for Mg, P and K in the non-specific response of Sitka spruce both to wounding, possibly as co-factors to enzymes and energy utilisation. The LA-ICP-MS method developed in this work proved useful to study spatial element distribution across bark samples and has great potential for applications in other areas of plant pathology research.

Draft Genome Sequences of Three Strains of Verticillium nonalfalfae Exhibiting Different Levels of Aggressiveness on Ailanthus altissima.

Verticillium nonalfalfae, a soilborne vascular fungus, shows promise for biocontrol of highly invasive Ailanthus altissima strains. This announcement provides draft genome sequences of the aggressive isolate G1/5 (wild-type strain), the highly aggressive isolate Vert56 (improved strain), and the mildly aggressive isolate I3/2, all obtained from symptomatic A. altissima trees in Austria.