Biocontrol ofAilanthus altissima: inoculation protocol and risk assessment forVerticillium nonalfalfae(Plectosphaerellaceae: Phyllachorales)

Abstract

Verticillium nonalfalfae has been proposed as a biocontrol for invasive Ailanthus altissima (tree-of-heaven) in Ohio, Pennsylvania and Virginia. However, previous studies evaluating this potential biocontrol utilised a conidial suspension with a short shelf life as inoculum. Anticipating future expanded use of V. nonalfalfae, we evaluated other inoculum formulations, inoculation protocols and sensitivity of non-target (non-Ailanthus) plant species within Pennsylvania. The most effective inoculum formulation, with an extended shelf life, was prepared by mixing water with stored, refrigerated soil containing V. nonalfalfae. Less successful, but positive infections were obtained by simply using infected Ailanthus wood and leaves as inoculum. Monthly inoculation of Ailanthus trees demonstrated that the optimal time for successful inoculations was April to May, but limited infections were achieved during all months, including the winter. The health of Ailanthus and non-target species was evaluated within a decade-old natural Verticillium wilt epicentre, where all mature Ailanthus trees had been killed by V. nonalfalfae. Verticillium wilt was observed on a few small Ailanthus trees, likely newly established seedlings, whereas non-target species were asymptomatic. Our findings reveal that soil formulated and natural inocula are effective biocontrols against Ailanthus, and V. nonalfalfae appears to pose little threat to non-target plants.

Natural distribution of Verticillium wilt on invasive Ailanthus altissima in eastern Austria and its potential for biocontrol

“…This might be the reason that 12 of 20 inoculated Ailanthus trees remained asymptomatic at subsite 3b and diminished MDS at that site. Slow colonization of V. nonalfalfae within Ailanthus due to high temperatures was already suggested byO'Neal and Davis (2015b).…”

First Report of Aleurocanthus spiniferus on Ailanthus altissima: Profiling of the Insect Microbiome and MicroRNAs

“…To the best of our knowledge, this is the first report of A. spiniferus infesting A. altissima. In fact, several studies have documented a number of pathogens and pests on A. altissima, but no mention of OSW has been reported [9][10][11][12][13]. This would suggest a host shift of OSW to A. altissima, but it cannot be excluded that the insect has infested this plant at extremely low population densities for a long time and it has not been observed or documented until now.…”

The Inability of Spotted Lanternfly (Lycorma delicatula) to Vector a Plant Pathogen between its Preferred Host, Ailanthus altissima, in a Laboratory Setting

“…Cultures of Verticillium nonalfalfae VnAa200/NRRL66918 [18] were grown on prune extract agar amended with streptomycin sulfate and neomycin sulfate (PEA + SN) [20] starting in mid-May 2019. After 2-5 weeks of growth, sterile 0.1% peptone in water was used to suspend V. nonalfalfae conidia at 10 7 conidia mL −1 for immediate use as an inoculum [14,15]. The germination rate of the inoculum was confirmed to be over 75% both before and after use by plating a subsample of the suspension on water agar and assessing germination after 24 h.…”

“…More recently, a very promising naturally occurring fungus found killing A. altissima in Pennsylvania (Verticillium nonalfalfae Inderb. (formerly Verticillium albo-atrum Reinke and Berthold) has also been the subject of biological control [13][14][15]. Movement of this vascular wilt pathogen within a stand through functional root grafts is rapid and can result in the local mortality of hundreds of A. altissima trees per year [15,16].…”