Characterization of pathogenic variants of Elsinoe fawcettii of citrus implies the presence of new pathotypes and cryptic species in Florida

Abstract

Elsinoe fawcettii causes scab disease in citrus worldwide. Many E. fawcettii isolates produce the phytotoxin elsinochrome that is required for fungal pathogenesis. We previously observed that most of the field-collected E. fawcettii isolates from Florida produced scab on rough lemon (Citrus jambhiri), grapefruit (Citrus paradisi), and sour orange (Citrus aurantium), belonging to the "Florida Broad Host Range" pathotype. A small portion of the isolates failed to induce scab on Sour orange, resembling the "Florida Narrow Host Range" pathotype. Of 71 isolates examined, 5 did not belong to either pathotype. In this study, we further investigated the pathological and genetic diversity of these isolates using three index hosts and molecular analyses. Isolate Ef10 was weakly virulent to grapefruit yet nonpathogenic to others isolate Ef17 induced strong necrosis on grapefruit and sour orange but not on rough lemon; isolates Ef29 and Ef49 were weakly virulent on rough lemon and grapefruit but nonpathogenic to Sour orange. Isolate Ef41 failed to produce detectable levels of elsinochrome and did not affect leaves of any species. This isolate produces smaller hyaline conidia compared with other isolates and is a genotypically distinct strain or subspecies as deduced from restriction fragment length polymorphisms and sequence analysis of both the internal transcribed spacer (ITS) of ribosomal DNA and beta-tubulin gene fragments and from random amplified polymorphic DNA fragments. Phylogenetic analysis based on the ITS1 region clearly differentiated isolate Ef41 from the other E. fawcettii isolates. Ef41 also displays very distinct extracellular activities of cell wall degrading enzymes and proteases. The results imply the presence of novel pathogenic variant or cryptic Subspecies of E. fawcettii that were not previously described in Florida.