Environment, dosage, and pathogen isolate moderate virulence in eelgrass wasting disease.

Area of Science:

• Marine biology
• Plant pathology
• Ecosystem health

Background:

• Eelgrass wasting disease, caused by *Labyrinthula zosterae*, threatens global eelgrass habitats.
• Environmental changes may influence the severity of this host-pathogen interaction.
• Limited understanding exists on how multiple environmental factors affect disease progression.

Purpose of the Study:

• To investigate the impact of *L. zosterae* isolate variation, pathogen dosage, temperature, and light on eelgrass disease severity.
• To determine how environmental factors influence *L. zosterae* growth and infection in eelgrass.

Main Methods:

• Laboratory trials inoculating eelgrass with three distinct *L. zosterae* isolates.
• Controlled experiments varying pathogen dosage (10^4 to 10^6 cells/mL).
• Two-way factorial experiments examining light (diel cycle vs. darkness) and temperature (11°C vs. 18°C) effects on *in vitro* growth and *in vivo* disease severity.

Main Results:

• Disease severity varied significantly among different *L. zosterae* isolates.
• Increased pathogen dosage led to higher disease severity.
• *L. zosterae* exhibited higher growth rates *in vitro* at warmer temperatures.
• Disease severity was greater in darkness and marginally affected by temperature in *in vivo* trials.

Conclusions:

• Pathogen isolate, increasing dosage, higher temperatures, and reduced light intensify eelgrass wasting disease severity.
• Photosynthesis appears crucial for eelgrass to mitigate disease progression.
• Changing environmental conditions are predicted to increase damage to eelgrass beds by *L. zosterae*.