Sporodochia formed by Fusarium oxysporum f. sp. fragariae produce airborne conidia and are ubiquitous on diseased strawberry plants in California

Abstract

Sporodochia are dense masses of fungal hyphae bearing asexual conidia. For Fusarium oxysporum, sporodochia are known to produce airborne conidia and enhance the dissemination of this otherwise soilborne pathogen. Sporodochia are small and transient, and they are documented for only a few formae speciales of Fusarium oxysporum. This study reports airborne conidia and sporodochia produced by F. oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry, in the Monterey Bay region of California. Sporodochia were consistently present in Fusarium wilt-afflicted strawberry fields and were discovered in 21 of 24 Fusarium wilt-diseased fields. Only necrotic tissues were observed bearing sporodochia, and they were most frequently observed on petioles and peduncles. Sporodochia grew significantly longer up peduncles than petioles, extending further away from the base of the plant and toward parts of the canopy more exposed to wind. A stolon hosted the longest stretch of sporodochial growth, found covering the stolons entire 35 cm length and also the base of the daughter plant. Macroconidia were produced by all sporodochia samples, and we did not find microconidia on any samples. An initial series of experiments confirmed the potential for conidia produced by sporodochia to disperse with wind over short distances. The prevalence of sporodochia producing airborne spores of F. oxysporum f. sp. fragariae has great importance for disease management and biosecurity.