Do halophytophthoras (marine Pythiaceae) rapidly occupy fallen leaves by intraleaf mycelial growth

Abstract

Low estimates (2 ∙ L−1) of concentrations of zoospores of Halophytophthora in mangrove water columns seem counterintuitive when compared with rapid rates of occupation of fallen mangrove leaves (100% frequency of occurrence after 24–30 h). One potential explanation is that lateral extension of mycelium within leaves is rapid after establishment of single zoospores. We tested this hypothesis by exposing single leaves in both mangrove and temperate salt-marsh ecosystems, with the upper half of leaves freely exposed to zoospore contact, and the lower half protected behind 8-μm screening. We found no evidence that mycelial growth within leaves was rapid enough to account for the rapid occupation of freely exposed leaves. Of the four Halophytophthora species commonly found (H. kandeliae, H. masteri, H. spinosa var. spinosa, and H. vesicula), only H. masteri appeared to have substantial capability for its zoospores to pass the screening. In temperate salt-marsh waters, H. kandeliae took the place of H. spinosa as co-occupier of leaves with H. vesicula. Two rare species (H. bahamensis and H. epistomium) originally described from subtropical mangrove environs were found in temperate salt-marsh samples. Key words: oomycotes, oomycetes, Halophytophthora, mangrove, salt marsh.