Abstract
Isolated boxwood endophytes have been demonstrated to effectively protect boxwood plants from infection by Calonectria pseudonaviculata (Cps). However, the roles of endophytes as communities in plant defense are not clear. Here, we demonstrated differential tolerance to Cps of English boxwood (Buxus sempervirens ‘Suffruticosa’), an iconic landscape plant and generally regarded as highly susceptible, and its link to endophyte complexity. Fifteen boxwood twig samples were collected in triplicates from three historic gardens—Colonial Williamsburg, George Washington’s Mount Vernon and River Farm, and Virginia Tech’s research farm in Virginia Beach in the summer and fall of 2019. A portion of individual samples was inoculated with Cps under controlled conditions. Significant differences in disease severity were observed among samples but not between the two seasons. Examining the endophyte cultures of the summer samples revealed that bacterial and fungal abundance was negatively and positively correlated with the disease severity. Nanopore metagenomics analysis on genomic DNA of the tolerant and susceptible group representatives confirmed the associations. Specifically, tolerant English boxwood plants had an endophyte community dominated by Bacilli and Betaproteobacteria, while susceptible ones had a distinct endophyte community dominated by Gammaproteobacteria, Actinobacteria, and diverse fungi. These findings may lead to boxwood health management innovations—devising and utilizing cultural practices to manipulate and increase the abundance and performance of beneficial endophytes for enhanced boxwood resistance to Cps.
Highlights
Introduction published maps and institutional affilBoxwood blight is a destructive fungal disease [1]
The sample twigs were evaluated for their tolerance to the boxwood blight pathogen, Calonectria pseudonaviculata (Cps)
English boxwood is generally considered highly susceptible to Cps, blight severity varied among the plants sampled (Figure 1)
Summary
Boxwood blight is a destructive fungal disease [1]. Among the most susceptible cultivars is English boxwood (Buxus sempervirens ‘Suffruticosa’), an iconic landscape plant in American and European gardens. The widespread planting of English boxwood, along with interstate and international trade of mass boxwood plant stocks, has presented an overwhelming challenge to blight prevention and control in private and public gardens as well as the ornamental horticulture industry [2,3]. The current boxwood plant protection paradigm relies largely on fungicide treatment, which is not sustainable and, in some cases, not practical. On the other hand, mulching is a common practice that prevents the blight pathogen in infested soil and diseased plant debris from water splash onto the foliage [4]. Mulching cannot prevent the pathogen from above-ground sources.
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