Identification and Characterization of Menadione and Benzethonium Chloride as Potential Treatments of Pierce's Disease of Grapevines.

Xylella fastidiosa infects a wide range of plant hosts and causes Pierce's disease (PD) of grapevines. The type 1 multidrug resistance (MDR) efflux system is essential for pathogenicity and survival of bacterial pathogens in planta. X. fastidiosa, with a single MDR system, is significantly more vulnerable to inhibition by small-molecule treatments than most bacterial pathogens that typically carry redundant MDR systems. A high-throughput cell viability assay using a green fluorescent protein-marked strain of X. fastidiosa Temecula 1 was developed to screen two Prestwick combinatorial small-molecule libraries of drugs and phytochemicals (1,600 chemicals in total) approved by the Food and Drug Administration and European Medicines Agency for cell growth inhibition. The screens revealed 215 chemicals that inhibited bacterial growth by >50% at 50 µM concentrations. Seven chemicals proved to lyse X. fastidiosa cells at 25 µM, including four phytochemicals. Menadione (2-methyl-1,4-naphthoquinone, vitamin K) from the phytochemical library and benzethonium chloride (a topical disinfectant) from the chemical library both showed significant bactericidal activity against X. fastidiosa. Both menadione and benzethonium chloride foliar spray (15 and 5 mM, respectively) and soil drench (5 and 25 mM, respectively) treatments were equally effective in reducing PD symptoms by 54 to 59% and revealed that the effects of both chemical treatments became systemic. However, menadione was phytotoxic when applied as a foliar spray at effective concentrations, causing significant loss of photosynthetic capacity.

Pythium spp. Isolated from Bermudagrass During Overseed Transitions in Florida and Pathogenicity of Pythium irregulare on Poa trivialis.

Pythium spp. were isolated from nonoverseeded bermudagrass and from bermudagrass overseeded with cool-season turfgrass species from October 2000 to July 2001 from two sites in Florida. Pythium spp. were isolated from nonoverseeded and overseeded, and fumigated and nonfumigated, bermudagrass plots from October 2001 to July 2002 from one of the two sites. The vast majority of isolates of Pythium spp. were obtained from the bermudagrass, rather than the cool-season turfgrass species (Poa trivialis or Lolium perenne) used as overseed. In the first year at the Ft. Lauderdale site, Pythium graminicola dominated (91% of isolates obtained). In the first year at the Gainesville site, P. graminicola (56% of isolates) and P. irregulare (36%) dominated; however, after fumigation and replanting, P. graminicola comprised only 11% of all isolates. P. irregulare comprised 30% of all isolates, but was found only in nonfumigated plots. A different species, P. ultimum var. ultimum, not isolated in the first year, was recovered (34% of isolates) from the replanted field in February and March. In preemergence pathogenicity tests, three of four isolates of P. irregulare were moderately to highly pathogenic on Poa trivialis, but not on L. perenne, and isolates of Pythium graminicola and P. ultimum var. ultimum were not pathogenic on either turfgrass species. Pathogenic Pythium spp. may survive from season to season on bermudagrass and, under favorable conditions, may cause damping-off or blight on the overseeded cool-season turfgrass.

Pythium spp. Associated with Bell Pepper Production in Florida.

Ten species of Pythium and a group of isolates that produced filamentous sporangia but did not form sexual structures (Pythium 'group F') were recovered from the root systems of fresh market bell pepper plants grown on polyethylene-mulched production systems in Florida. Pathogenicity tests using pasteurized field soil inoculated with infested wheat seed demonstrated that P. aphanidermatum, P. myriotylum, P. helicoides, and P. splendens can cause significant root rot and reductions in root growth of pepper. P. aphanidermatum and P. myriotylum caused the most severe root rot, the greatest reductions in plant weight, and 42 and 62% plant mortality, respectively. In pathogenicity tests with tomato plants, these four species produced similar plant weight losses and disease ratings to those observed in pepper, but little or no plant mortality. Low incidences of root tip necrosis in pepper plants were observed with P. arrhenomanes, P. catenulatum, P. graminicola, and P. irregulare, but none of these species caused losses in root weight and only P. irregulare reduced shoot weight. P. periplocum, P. spinosum, and Pythium sp. F colonized root tissue of pepper but caused no significant root rot and did not adversely affect growth. Similar trends were observed with tomato, except that P. arrhenomanes caused limited root tip necrosis without affecting plant growth and P. catenulatum, P. graminicola, P. irregulare, P. spinosum, and Pythium sp. F colonized at least some of the plants but did not cause root disease. A significant interaction between temperature and P. aphanidermatum or P. myriotylum was observed on pepper transplants. The greatest reductions in growth occurred at 28°C, whereas plant mortality only occurred at 34°C.