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.

In the spring of 1996, severe blossom blight occurred in some strawberry fruit production fields in the Watsonville area. The symptoms, in addition to blighting of entire flowers, were as follows: on the lower surface of the calyx, watersoaked lesions that appeared dark green under reflected light and translucent under transmitted light; necrotic calyces of seemingly healthy green and ripe fruits; watersoaking of the base of the calyx that extended into the pedicel; green-gray sporulation on dead anthers; and presence of flower clusters with small and irregularly shaped fruits. Yellow bacterial colonies were consistently isolated from water-soaked and necrotic lesions on calyces and pedicels. These colonies were entire, circular, raised, glistening, mucoid, and slow growing, characteristics typical of Xanthomonas fragariae on nutrient agar-glucose-yeast extract medium. The bacterial isolate was also identified by rep-polymerase chain reaction as X. fragariae. In addition to the yellow bacteria, a fungus was also frequently isolated from infected anthers, sepals, petals, and pistils, and was identified as Cladosporium cladosporioides. On potato dextrose agar, the fungus had velvetlike colonies colored olivaceous-green to olivaceous-brown, apically and laterally branched conidiophores, and lemon-shaped conidia that were usually smooth but sometimes textured. Blossoms of greenhouse-grown strawberry plants cv. Selva were inoculated with either or both organisms. Blossoms inoculated with X. fragariae developed symptoms distinct from those inoculated with C. cladosporioides. The most prominent visible symptoms caused by X. fragariae were watersoaked lesions on calyces that later became necrotic, watersoaking of the calyx that extended into the pedicel, and blighting of flowers and developing fruits as a result of girdling of the pedicel. Infection by C. cladosporioides was characterized by necrosis of flower parts or the entire flower, presence of green-gray sporulation on dead anthers, and production of small and malformed or misshapen fruits. Inoculation with both organisms produced all the symptoms described above in different flowers of a plant. Infection with both organisms aggravated disease severity, but each organism was capable of inducing blossom blight independently. Both organisms were reisolated from artificially inoculated strawberry flowers, fulfilling Koch's postulate for proof of pathogenicity. This is the first report of the two organisms causing blossom blight of strawberry in California. This is also the first report that C. cladosporioides is a pathogen of strawberry.

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.

Blossom blight was documented in some strawberry production fields in Watsonville in 1996 and 1997. Xanthomonas fragariae and Cladosporium cladosporioides were identified as the causal organisms. This is the first documentation of the two organisms causing blossom blight of strawberry in California. This is also the first report identifying C. cladosporioides as a pathogen of strawberry.

Differential tolerance of English boxwood to boxwood blight has been linked to the ratio of culturable bacterial and fungal dominance in the leaf tissue of representative samples. To further understand how the whole endophyte communities may involve the tolerance of large samples, we extracted DNA from healthy leaf tissue of previously identified 28 tolerant (T), 41 moderately tolerant (M) and 21 susceptible (S) English boxwood plants, then sequenced associated bacterial and fungal amplicons using the Nanopore MinION platform. The endophyte community did not differ in diversity among the T, M, and S plants, but differed in the abundance of bacteria and fungi, particularly between T and S samples. The bacterial genera Brevundimonas and Ammonifex had higher relative abundance in the T and M communities than in the S community which was more dominant by the fungal genera Botrytis, Thermothelomyces and Chaetomiaceae. The same results were obtained when mother and daughter samples in the T community were compared with controls in the S community, suggesting bacteria as a work force in the T community. Co-occurrence network analyses revealed that the T network had more fungal hubs but less complex with more positive connections than the S network, suggesting that the T community was supported by a healthier network. The resistance of English boxwood to blight is likely attributed to bacteria dominance and a synergic community network. This study is foundational to constructing synthetic communities and using whole communities of tolerant plants through vegetative propagation for microbe-modulated immunity.