Differential Tolerance to Calonectria pseudonaviculata of English Boxwood Plants Associated with the Complexity of Culturable Fungal and Bacterial Endophyte Communities.

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.

In Vitro Enhancement of Antibiotic Resistance Development-Interaction of Residue Levels of Pesticides and Antibiotics †.

This study investigated the interaction of three commonly used pesticides, carbaryl, captan, and malathion, with combinations of antibiotics occurring commonly in milk, all at levels below established tolerances. The modality of measurement was the MIC; the assay organism was Staphylococcus aureus ATCC 9144. Acetone alone or individual pesticides in acetone caused no increase in the baseline MIC of any of the marker antibiotics. For single antibiotics, (ampicillin, dihydrostreptomycin, erythromycin, neomycin, oxytetracycline, and sulfamethazine) 7.1 % of the combination possibilities showed increased MICs. The three pesticides together resulted in an increased MIC in 4.8% of the combinations. Varying combinations of three of the aforelisted antibiotics showed increases in the baseline MIC in 18.5% of the possibilities. Combinations of three antibiotics and the three pesticides showed increased MICs in 24.4% of the possibilities. There appears to be an additive effect upon the development of antibiotic resistance of S. aureus cells between the three pesticides and the antibiotics in the combinations studied.