Use of the vital stain FUN-1 indicates viability of Phytophthora capsici propagules and can be used to predict maximum zoospore production

Abstract

The fluorescent vital dye FUN®-1 (2-chloro-4-[2,3-dihydro-3-methyl-{benzo-1,3-thiazol-2-yl}-methylidene]-1-phenylquinolinium iodide) was evaluated as a tool to assess Phytophthora capsici sporangia and zoospore metabolic activity and viability. Under aerobic conditions, mycelia, sporangia and zoospores cultured on agar medium and stained with FUN-1 exhibited red fluorescent cylindrical intravacuolar structures (CIVS) that were clearly visible at 100× magnification. Encysted zoospores did not exhibit CIVS after exposure to FUN-1 dye. Over 7 d there was a significant reduction in the percent of sporangia containing CIVS, which corresponded with a significant increase in zoospore formation and release. The decline in the percentage of metabolically active sporangia and increase in the number of zoospores fit both a linear and log regression model. The FUN-1 dye was suitable for distinguishing between live and dead sporangia and effective in monitoring the change in metabolic activity of sporangia over time. It will be useful in determining parameters, including P. capsici culture age, that maximize production of zoospores in vitro.

• cylindrical intravacuolar structures (CIVS)
• encysted zoospores
• sporangia
• vital dye
• zoospores

Acknowledgments

The Ohio Agricultural Research and Development Center (OARDC) Research Enhancement Competitive Grants Program (SEEDS) and the Ohio Vegetable and Small Fruit Research and Development Program supported this work.

Notes

2 Chlorine-based residues remaining on P. capsici isolate SAM16-10 sporangia after exposure to chlorine dioxide and sodium hypo-chlorite have a bleaching effect on FUN-1 vital dye (Lewis Ivey 2011).