Dispersal gradients of conidia of the butternut canker fungus in a forest during rain

Abstract

Dispersal gradients of conidia of Sirococcusclavigignenti-juglandacearum Nair, Kostichka, and Kuntz, the causal agent of butternut canker, were studied in the forest for various rainfall dates. During rain, large numbers of conidia from branch cankers were carried in runoff water down the tree trunks of butternut (Juglanscinerea L.), causing infections that resulted in trunk cankers. Conidia also were dispersed in small droplets or aerosols and disseminated up to 40 m from a cankered tree during rainfall. Concentrations of conidia in the air decreased exponentially with increasing distances from the inoculum source. Dispersal gradients were influenced by stand composition and (or) size of the inoculum source, with steeper gradients associated with a dense forest canopy and a small area source of inoculum. Weather conditions, excluding the necessity for rain, had little influence in altering dispersal gradients within the same stand for different rainfall dates.