The Response of Botrytis cinerea to Fire in a Coast Redwood Forest

Coast redwoods (Sequoia sempervirens) are long-lived trees that create deep shade and litter layers, and have limited recruitment from seedlings. Botrytis cinerea is an airborne fungal pathogen that attacks redwood seedlings. B. cinerea lives as a saprotroph in dead plant matter or as a necrotroph in live tissue. In the coast redwood forest, accumulated leaf litter may provide inoculum for subsequent infections, limiting redwood seedling recruitment. Here, we examine the response of B. cinerea to fire in the coast redwood forest. We measured the abundance of airborne B. cinerea spores in paired burned and unburned plots using a selective and diagnostic medium. In a greenhouse experiment, we grew seedlings in four different treatments: (1) burned soil with no leaf litter, (2) unburned soil with no leaf litter, (3) burned soil with leaf litter collected from the burn plot, (4) unburned soil with leaf litter collected from the unburned plot. Spore trapping showed no difference in the abundance of airborne spores in the paired plots. The seedling experiment showed that disease was greatest and survival lowest when grown in burned soil; leaf litter collected from burned plots reduced survival while leaf litter from not-burned plots increased survival. These results indicate that fire did not affect airborne B. cinerea and post-fire conditions did not provide favorable growth conditions for coast redwood seedlings.