Abstract
BackgroundThe genus Phytophthora includes a group of agriculturally important pathogens and they are commonly regarded as water molds. They produce motile zoospores that can move via water currents and on their own locomotion in aquatic environments. However, zoosporic response to dissolved oxygen, an important water quality parameter, is not known. Like other water quality parameters, dissolved oxygen concentration in irrigation reservoirs fluctuates dramatically over time. The aim of this study was to determine whether and how zoospore survival may be affected by elevated and low concentrations of dissolved oxygen in water to better understand the aquatic biology of these pathogens in irrigation reservoirs.ResultsZoospores of P. megasperma, P. nicotianae, P. pini and P. tropicalis were assessed for survival in 10% Hoagland’s solution at a range of dissolved concentrations from 0.9 to 20.1 mg L-1 for up to seven exposure times from 0 to 72 h. Zoospore survival was measured by resultant colony counts per ml. Zoospores of these species survived the best in control Hoagland’s solution at dissolved oxygen concentrations of 5.3 to 5.6 mg L-1. Zoospore survival rates decreased with increasing and decreasing concentration of dissolved oxygen, depending upon Phytophthora species and exposure time. Overall, P. megasperma and P. pini are less sensitive than P. nicotianae and P. tropicalis to hyperoxia and hypoxia conditions.ConclusionZoospores in the control solution declined over time and this natural decline process was enhanced under hyperoxia and hypoxia conditions. These findings suggest that dramatic fluctuations of dissolved oxygen in irrigation reservoirs contribute to the population decline of Phytophthora species along the water path in the same reservoirs. These findings advanced our understanding of the aquatic ecology of these pathogens in irrigation reservoirs. They also provided a basis for pathogen risk mitigation by prolonging the turnover time of runoff water in recycling irrigation systems via better system designs.
Highlights
The genus Phytophthora includes a group of agriculturally important pathogens and they are commonly regarded as water molds
Effect of dissolved nitrogen on zoospore survival In preliminary studies using hydrazine hydrate and CO2 to manipulate dissolved oxygen concentration in Hoagland’s solution, we found that both chemicals themselves significantly reduced zoospore survival [10,22]
In this study we showed for the first time the zoosporic responses to oxygen stress of four economically important species of Phytophthora in a simulated aquatic system
Summary
The genus Phytophthora includes a group of agriculturally important pathogens and they are commonly regarded as water molds They produce motile zoospores that can move via water currents and on their own locomotion in aquatic environments. The aim of this study was to determine whether and how zoospore survival may be affected by elevated and low concentrations of dissolved oxygen in water to better understand the aquatic biology of these pathogens in irrigation reservoirs. Phytophthora species, a group of fungal-like destructive plant pathogens, are known as water molds [1,2,3,4] They produce motile zoospores that can spread through irrigation systems from runoff water retention basins at ornamental crop production facilities and cause severe plant diseases and crop losses. Zoospore survival of individual species in aquatic environments depends upon water pH [7,9], electrical conductivity (EC) [6], and CO2 [10,11]
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