Bacterial spot of pepper (BSP) is an important disease caused by Xanthomonas spp. Copper-based bactericides have been widely used to manage this disease over the decades. This has resulted in the development of copper resistance in the pathogen. To this date, as a standard practice, mancozeb mixed with a copper material has been used instead of copper alone to control copper-tolerant strains of the BSP pathogen. As a result of the build-up of copper-tolerant strains, there is a need for an alternative to copper bactericides. Based on results of previous studies for control of bacterial spot-on tomato, we tested core-shell silica copper (CS-Cu), a copper-based nanomaterial as well as some magnesium-based nanomaterials like magnesium oxide (MgO), magnesium double coated copper (MgDC) and magnesium copper (MgCu) in vitro and in planta against X. euvesicatoria. In the in vitro experiments, all nanomaterials had bactericidal activity at concentrations as low as 200 ppm, ranging from 100-fold reduction to complete elimination of viable bacterial cells as compared to the commercial copper bactericide (Kocide 3000) and the control. In growth chamber experiments all the nanomaterials at 100 mu g/ml or higher reduced disease severity ranging from 15 % to 56 % less disease compared to theuntreated control. In field experiments nanomaterials except MgO and MgCu at 100 mu g/ml were able to reduce BSP severity ranging from 12 % to 50 % compared to untreated control, whereas their efficacy remained similar to that of Kocide-3000.

Bacterial spot of tomato (BST), predominantly caused by Xanthomonas perforans (Xp) in Florida, is one of the most devastating diseases in hot, humid environments. Bacterial resistance to copper-based bactericides and antibiotics makes disease management extremely challenging. This necessitates alternative new solutions to manage the disease. In this study, we used two novel hybrid copper and magnesium nanomaterials, noted as magnesium double-coated (Mg-Db) and magnesium-copper (Mg-Cu), to manage BST. In in vitro experiments, no viable cells were recovered following 4 h of exposure to 500 μg/ml of both Mg-Db and Mg-Cu, while 100 and 200 μg/ml required 24 h of exposure for complete inhibition. In a viability assay using the live/dead cell straining method and epifluorescence microscopy, copper-tolerant Xp cells were killed within 4 h by both Mg-Cu and Mg-Db nanomaterials at 500 μg/ml but not by copper hydroxide (Kocide 3000). In the greenhouse, Mg-Db and Mg-Cu at 100 to 500 μg/ml significantly reduced BST severity compared with micron-sized commercial copper bactericide Kocide 3000 and the growers' standard (copper hydroxide + mancozeb) (P < 0.05). In field studies, Mg-Db and Mg-Cu nanomaterials significantly reduced disease severity in two out four field trials. Mg-Db at 500 μg/ml reduced BST severity by 34% compared with the nontreated control without affecting yield in fall, 2020. The use of hybrid nanomaterials at the highest concentrations (500 μg/ml) evaluated in the field experiments can reduce copper use by 90% compared with the growers' standard. In addition, there was no phytotoxicity observed with the use of hybrid nanomaterials in the field. These results suggest the potential of novel magnesium-copper-based hybrid nanomaterials to manage copper-tolerant bacterial pathogens.

Bacterial spot of tomato is among the most economically relevant diseases affecting tomato plants globally. In previous studies, non-formulated magnesium oxide nanoparticles (nano-MgOs) significantly reduced the disease severity in greenhouse and field conditions. However, the aggregation of nano-MgO in liquid suspension makes it challenging to use in field applications. Therefore, we formulated two novel MgO nanomaterials (SgMg #3 and SgMg #2.5) and one MgOH2 nanomaterial (SgMc) and evaluated their physical characteristics, antibacterial properties, and disease reduction abilities. Among the three Mg nanomaterials, SgMc showed the highest efficacy against copper-tolerant strains of Xanthomonas perforans in vitro, and provided disease reduction in the greenhouse experiments compared with commercial Cu bactericide and an untreated control. However, SgMc was not consistently effective in field conditions. To determine the cause of its inconsistent efficacy in different environments, we monitored particle size, zeta potential, morphology, and crystallinity for all three formulated materials and nano-MgOs. The MgO particle size was determined by the scanning electron microscopy (SEM) and dynamic light scattering (DLS) techniques. An X-ray diffraction (XRD) study confirmed a change in the crystallinity of MgO from a periclase to an Mg(OH)2 brucite crystal structure. As a result, the bactericidal activity correlated with the high crystallinity present in nano-MgOs and SgMc, while the inconsistent antimicrobial potency of SgMg #3 and SgMg #2.5 might have been related to loss of crystallinity. Future studies are needed to determine which specific variables impair the performance of these nanomaterials in the field compared to under greenhouse conditions. Although SgMc did not lead to significant disease severity reduction in the field, it still has the potential to act as an alternative to Cu against bacterial spot disease in tomato transplant production.

A field survey was conducted in Florida during 2020-2021 in squash and pumpkin research fields to identify the viruses associated with leaf symptoms of yellowing, crumpling, and vein yellowing. The symptoms were similar to previously reported whitefly transmitted viruses such as cucurbit leaf crumple virus (CuLCrV), cucurbit yellow stunting disorder virus (CYSDV), and squash vein yellowing virus (SqVYV). Another potential virus of interest was the cucurbit chlorotic yellows virus (CCYV) that was recently reported on watermelon in Florida. Symptomatic leaves were tested by RT-PCR with coat protein (CP) gene-specific (GS) primers for CuLCrV, CYSDV, CCYV, and SqVYV with nuclear inclusion protein (NIa) GS primers. Amplifications for CuLCrV, CYSDV, and CCYV were detected in squash and pumpkin samples. The CCYV amplicons were further sequenced and compared with available CCYV sequences. The NCBI BLAST analysis revealed similarities of the RdRP (100%), HSP70h (99.75%), and CP (99.75%) to the Shanghai CCYV isolates (RNA KY400636 and RNA2 KY400633). To our knowledge, this is the first report of CCYV on squash and pumpkin in Florida.

Rose rosette disease (RRD) caused by rose rosette emaravirus (RRV) is a major issue in the U.S. rose industry with no effective method for its management. This study evaluated the effect of foliar application of acibenzolar-S-methyl (ASM), a plant systemic acquired resistance inducer, in reducing RRD disease severity on Rosa species cv. Radtkopink ('Pink Double Knock Out') under greenhouse conditions, and the effect of ASM on plant growth under commercial nursery production conditions. ASM at 50- or 100-mg/liter concentrations at weekly intervals significantly reduced RRD severity compared with the untreated control in two of the three greenhouse trials (P < 0.05). The plants in these trials were subsequently pruned and observed for symptoms, which further indicated that application of ASM at 50- or 100-mg/liter concentrations lowered disease severity compared with the untreated control (P < 0.05) in these two trials. Plants treated with ASM at 50- or 100-mg/liter concentrations had delayed incidence of RRD compared with the nontreated controls. Plants treated with ASM at the 50- or 100-mg/liter rate in all three trials either did not have RRV present or the virus was present in fewer leaf samples than untreated controls as indicated by quantitative reverse transcription PCR analysis. Overall, plants treated with ASM at the 50-mg/liter concentration had 36 to 43% reduced RRD incidence compared with the water control. The treatment of two cultivars of rose, 'Radtkopink' and 'Meijocos' ('Pink Drift'), with weekly foliar applications of ASM at the three rates (0.5, 0.75, and 1.0 oz/A) indicated that ASM had no negative effect on flowering or plant growth at even the highest rate of application.

On April 2017, four out of 10,000 Double Knock Out Red roses were observed presenting partially wilted and chlorotic foliage in a commercial nursery in Gadsden Co., Florida. Closer examination of the plant crown revealed brown discoloration of the woody tissue. Under high temperature (85°F) and humidity (70%), shoots progressively turned chlorotic and necrotic, leading to plant death in 4 months. A rapid-growing fungus presenting orange-brown mycelium and abundant cylindrical spores was isolated from infected woody crown tissue. BLAST analysis of the resulting sequence (GenBank no. MT019606) of this pathogen had 100% identity to Calonectria cylindrospora β-tubulin gene (GenBank no. FJ918509.1). Koch’s postulates were conducted on healthy Double Knock Out roses. Two weeks after inoculation, shoots of inoculated plants turned progressively chlorotic and then necrotic, leading to plant death in 2 months. The same pathogen was reisolated from infected plant parts, which sequence also had 100% identity to C. cylindrospora β-tubulin gene (GenBank no. FJ918509.1). This pathogen is the same as one of three isolated from crown rot of roses back in 1994 and identified as Cylindrocladium scoparium (teleomorph: C. cylindrospora [Ellis & Everh.]). In this new occurrence, all infected plants were removed from the nursery, and no further infections were detected. This finding is important for commercial growers to be aware of the potential presence of this pathogen in their nurseries. Knowing the symptoms will help them recognize the disease and take action to prevent spread of the disease.

A hybrid core–shell silica nanoparticle system integrating Cu nanoclusters and Quat combats resistance development of Xanthomonas perforans responsible for bacterial spot disease of tomatoes.

Copper (Cu) is the most extensively used bactericide worldwide in many agricultural production systems. However, intensive application of Cu bactericide have increased the selection pressure toward Cu-tolerant pathogens, including Xanthomonas perforans, the causal agent of tomato bacterial spot. However, alternatives for Cu bactericides are limited and have many drawbacks including plant damage and inconsistent effectiveness under field conditions. Also, potential ecological risk on nontarget organisms exposed to field runoff containing Cu is high. However, due to lack of alternatives for Cu, it is still widely used in tomato and other crops around the world in both conventional and organic production systems. In this study, a Cu-tolerant X. perforans strain GEV485, which can tolerate eight tested commercial Cu bactericides, was used in all the field trials to evaluate the efficacy of MgO nanomaterial. Four field experiments were conducted to evaluate the impact of intensive application of MgO nanomaterial on tomato bacterial spot disease severity, and one field experiment was conducted to study the impact of soil accumulation of total and bioavailable Cu, Mg, Mn, and Zn. In the first two field experiments, twice-weekly applications of 200 μg/mL MgO significantly reduced disease severity by 29-38% less in comparison to a conventional Cu bactericide Kocide 3000 and 19-30% less in comparison to the water control applied at the same frequency (p = 0.05). The disease severity on MgO twice-weekly was 12-32% less than Kocide 3000 + Mancozeb treatment. Single weekly applications of MgO had 13-19% higher disease severity than twice weekly application of MgO. In the second set of two field trials, twice-weekly applications of MgO at 1000 μg/mL significantly reduced disease severity by 32-40% in comparison to water control applied at the same frequency (p = 0.05). There was no negative yield impact in any of the trials. The third field experiment demonstrated that application of MgO did not result in significant accumulation of total and bioavailable Mg, Mn, Cu, or Zn in the root-associated soil and in soil farther away from the production bed compared to the water control. However, Cu bactericide contributed to significantly higher Mn, Cu, and Zn accumulation in the soil compared to water control (p = 0.05). This study demonstrates that MgO nanomaterial could be an alternative for Cu bactericide and have potential in reducing risks associated with development of tolerant strains and for reducing Cu load in the environment.

Bacterial spot disease caused by Xanthomonas euvesicatoria is one of the major constraints for pepper production in Florida and worldwide. The common prevalence of copper (Cu)-tolerant X. euvesicatoria strains has reduced the efficacy of Cu based bactericides against bacterial spot of pepper. In this study, we evaluated antimicrobial activity of three Cu-based nanocomposites, namely, core-shell Cu (CS-Cu), fixed-quat Cu (FQ-Cu) and mixed-valence Cu (MV-Cu), along with Kocide (R) 3000, which is a micron size metallic Cu bactericide and is commercially available, both in vitro and in greenhouse trials, against a Cu-tolerant strain of X. euvesicatoria. In repeated in vitro tests, X. euvesicatoria growth was completely inhibited 24 h after exposure of bacterial cells to 500 and 1000 mu g/ml of MV-Cu and all concentrations of FQ-Cu and CS-Cu (100, 200, 500, and 1000 mu g/ml) treated for 1 h. Micron size copper, even at 1000 mu g/ml, had no statistical difference in growth in comparison to the untreated control (P = 0.05; LSD). In the repeated greenhouse experiments, plants treated with all the copper composites exhibited less bacterial spot severity than untreated control and similar or significantly less than Cu-ancozeb (P < 0.05). However, MV-Cu was the only Cu composite with no phytotoxicity on plants under controlled conditions. This study shows potential to use Cu-based nanoparticles for efficient management of bacterial spot on pepper.

Multispectral imaging is increasingly used in specialty crops, but its benefits in assessment of disease severity and improvements in conventional scouting practice are unknown. Multispectral imaging was conducted using an unmanned aerial vehicle (UAV), and data were analyzed for five flights from Florida and Georgia commercial watermelon fields in 2017. The fields were rated for disease incidence and severity by extension agents and plant pathologists at randomized locations (i.e., conventional scouting) followed by ratings at locations that were identified by differences in normalized difference vegetation index (NDVI) and stress index (i.e., UAV-assisted scouting). Diseases identified by the scouts included gummy stem blight, anthracnose, Fusarium wilt, Phytophthora fruit rot, Alternaria leaf spot, and cucurbit leaf crumple disease. Disease incidence and severity ratings were significantly different between conventional and UAV-assisted scouting (P < 0.01, Bhapkar/exact test). Higher severity ratings of 4 and 5 on a scale of 1 to 5 from no disease to complete loss of the canopy were more consistent after the scouts used the multispectral images in determining sampling locations. The UAV-assisted scouting locations had significantly lower green, red, and red edge NDVI values and higher stress index values than the conventional scouting areas (P < 0.05, ANOVA/Tukey), and this corresponded to areas with higher disease severity. Conventional scouting involving human evaluation remains necessary for disease validation. Multispectral imagery improved watermelon field scouting owing to increased ability to identify disease foci and areas of concern more rapidly than conventional scouting practices with early detection of diseases 20% more often using UAV-assisted scouting.

Rose mosaic virus disease is one of the most economically important diseases affecting roses, because a single symptomatic leaf can result in the rejection of complete shipments for wholesale or retail rose producers. It continues to be a problem in nursery production and landscapes. This 5-page document discusses the causes, symptoms, and management of this disease. Written by Susannah da Silva, Binoy Babu, Mathews L. Paret, Gary Knox, Fanny Iriarte, Barron Riddle, Matt Orwat, Shawn T. Steed, E. Vanessa Campoverde, and Svetlana Y. Folimonova and published by the UF/IFAS Plant Pathology Department, August 2018. http://edis.ifas.ufl.edu/pp338/

Rhizobium radiobacter (also known as Agrobacterium tumefaciens), has been reported to be found on more than 600 different plant species worldwide including many common vegetables, weeds, deciduous and evergreen trees and shrubs. This document discusses the biology, symptom expression, and management of this bacterium.