Engineered nanoparticles are materials between 1 and 100 nm and exist as metalloids, metallic oxides, nonmetals, and carbon nanomaterials and as functionalized dendrimers, liposomes, and quantum dots. Their small size, large surface area, and high reactivity have enabled their use as bactericides/ fungicides and nanofertilizers. Nanoparticles can be designed as biosensors for plant disease diagnostics and as delivery vehicles for genetic material, probes, and agrichemicals. In the past decade, reports of nanotechnology in phytopathology have grown exponentially. Nanomaterials have been integrated into disease management strategies and diagnostics and as molecular tools. Most reports summarized herein are directed toward pathogen inhibition using metalloid/metallic oxide nanoparticles as bactericides/fungicides and as nanofertilizers to enhance health. The use of nanoparticles as biosensors in plant disease diagnostics is also reviewed. As global demand for food production escalates against a changing climate, nanotechnology could sustainably mitigate many challenges in disease management by reducing chemical inputs and promoting rapid detection of pathogens.

Nanoparticles (NP) have great potential in agriculture. For example, micronutrients have poor mobility in plants and poor availability in neutral soils, yet they play pivotal roles in root health. We investigated whether foliar sprays of micronutrient NP could affect plant health in disease infested soils. In the greenhouse, NP of AlO, CuO, FeO, MnO, NiO, and ZnO were sprayed on tomatoes and grown in soilless medium infested with the Fusarium wilt fungus. NP of CuO, MnO, or ZnO reduced disease estimates [area-under-the-disease-progress-curve (AUDPC)] by 31%, 28%, or 28%, respectively, when compared to untreated controls. When NP of CuO, MnO, or ZnO, their bulked equivalents, or their sulfate salts were compared to untreated eggplants and held in the greenhouse in soilless medium infested with the Verticillium wilt fungus, NP of CuO increased fresh weights by 64%, reduced AUDPC values by 69%, and had 32% more Cu in the roots. These same amendments were sprayed onto the foliage of tomato and eggplant transplants and set in field plots in soil heavily infested with the Verticillium wilt fungus. Compared to untreated controls, yields of tomato were 33% or 31% greater with NP of CuO or the bulked MnO, respectively. NP of CuO or ZnSO₄ increased eggplant yields by 34% or 41% when compared to controls, respectively. In vitro studies found NP of CuO were not inhibitory to the Fusarium wilt fungus, suggesting host defense was being manipulated.

Pyrolyzed biomass waste, commonly called biochar, has attracted interest as a soil amendment. A commercial prototype biochar produced by fast pyrolysis of hardwood dust was examined in soils to determine if it could reduce the damaging effect of allelopathy on arbuscular mycorrhizal (AM) root colonization and on Fusarium crown and root rot of asparagus. In greenhouse studies, biochar added at 1.5 and 3.0% (wt/wt) to asparagus field soil caused proportional increases in root weights and linear reductions in the percentage of root lesions caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum compared with a control. Concomitant with these effects was a 100% increase in root colonization by AM fungi at the 3.0% rate. Addition of aromatic acids (cinnamic, coumaric, and ferulic) that are known allelopathic agents affecting asparagus reduced AM colonization but the deleterious effects were not observed following the application of biochar at the higher rate. When dried, ground, asparagus root and crown tissues infested with Fusarium spp. were added to soilless potting mix at 0, 1, or 5 g/liter of potting mix and then planted with asparagus, there was a decrease in asparagus root weight and increase in disease at 1 g/liter of potting mix but results were inconsistent at the higher residue rate. However, when biochar was added at 35 g/liter of potting mix (roughly 10%, vol/vol), these adverse effects on root weight and disease were equal to the nontreated controls. A small demonstration was conducted in field microplots. Those plots amended with biochar (3.5% [wt/wt] soil) produced asparagus plants with more AM colonization in the first year of growth but, in the subsequent year, biochar-treated plants were reduced in size, possibly due to greater than average precipitation and the ability of biochar to retain moisture that, in turn, may have created conditions conducive to root rot. These studies provide evidence that biochar may be useful in overcoming the deleterious effects of allelopathic residues in replant soils on asparagus.

Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user’s needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

This study explored the use of foliar sprays with nanoparticles (NP) of B, CuO, MnO, SiO, TiO, and ZnO to protect watermelon against Fusarium wilt. Leaves of young watermelon plants were sprayed (1 to 2 ml per plant) with NP suspensions (500 to 1,000 µg/ml) and were planted in potting mix infested with Fusarium oxysporum f. sp. niveum. In five of eight greenhouse experiments, CuO NP suppressed disease and, in six of eight experiments, CuO NP increased biomass or yield more than in untreated controls or other tested NP. More root Cu was detected in CuO NP-treated plants than other treatments (P = 0.015). In Griswold, CT, plants treated with CuO NP yielded 39% more fruit than untreated controls. In Hamden, CT, treatment with CuO NP produced 53% more fruit when compared with controls (P = 0.02) and was superior to other Cu fungicides. Gene expression in watermelon roots revealed strong upregulation of polyphenol oxidase (PPO) and PR1 genes when CuO NP and F. oxysporum f. sp. niveum were both present. Enzymatic assays for PPO supported the gene expression results. CuO NP may serve as a highly effective delivery agent for this micronutrient to suppress disease.

Nanoparticles are used in a variety of products, including fertilizer-nutrients and agro-pesticides. However, due to heightened reactivity of nano-scale materials, the effects of nanoparticle nutrients on crops can be more dramatic when compared to non nano-scale nutrients. This study evaluated the effect of nano manganese-(Mn) on wheat yield and nutrient acquisition, relative to bulk and ionic-Mn. Wheat was exposed to the Mn types in soil (6 mg/kg/plant), and nano-Mn was repeated in foliar application. Plant growth, grain yield, nutrient acquisition, and residual soil nutrients were assessed. When compared to the control, all Mn types significantly (p < 0.05) reduced shoot N by 9–18%. However, nano-Mn in soil exhibited other subtle effects on nutrient acquisition that were different from ionic or bulk-Mn, including reductions in shoot Mn (25%), P (33%), and K (7%) contents, and increase (30%) in soil residual nitrate-N. Despite lowering shoot Mn, nano-Mn resulted in a higher grain Mn translocation efficiency (22%), as compared to salt-Mn (20%), bulk-Mn (21%), and control (16%). When compared to soil, foliar exposure to nano-Mn exhibited significant differences: greater shoot (37%) and grain (12%) Mn contents; less (40%) soil nitrate-N; and, more soil (17%) and shoot (43%) P. These findings indicate that exposure to nano-scale Mn in soil could affect plants in subtle ways, differing from bulk or ionic-Mn, suggesting caution in its use in agriculture. Applying nano Mn as a foliar treatment could enable greater control on plant responses.