Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L.

Abstract

Here, we address the morphological changes of eyed eggs of Atlantic salmon, Salmo salar L. infected with Saprolegnia from a commercial hatchery and after experimental infection. Eyed eggs infected with Saprolegnia spp. from 10 Atlantic salmon females were obtained. Egg pathology was investigated by light and scanning electron microscopy. Eggs from six of ten females were infected with S. parasitica, and two females had infections with S. diclina clade IIIA; two Saprolegnia isolates remained unidentified. Light microscopy showed S. diclina infection resulted in the chorion in some areas being completely destroyed, whereas eggs infected with S. parasitica had an apparently intact chorion with hyphae growing within or beneath the chorion. The same contrasting pathology was found in experimentally infected eggs. Scanning electron microscopy revealed that S. parasitica grew on the egg surface and hyphae were found penetrating the chorion of the egg, and re‐emerging on the surface away from the infection site. The two Saprolegnia species employ different infection strategies when colonizing salmon eggs. Saprolegnia diclina infection results in chorion destruction, while S. parasitica penetrates intact chorion. We discuss the possibility these infection mechanisms representing a necrotrophic (S. diclina) vs. a facultative biotrophic strategy (S. parasitica).

A Review: Factors Affecting Outbreaks of Saprolegniosis on Aquatic Animals

“…In an experiment with live and dead Atlantic salmon eyed eggs which were infected with eight different Saprolegnia isolates, all isolates were only able to grow on dead eggs (Thoen et al, 2011). However, this differs from the results of Songe et al (2016) who claimed that S. parasitica was wildly attracted to eyed eggs of Salmo salar L., believing that there might be a possible facultative biotrophic mechanism by S. parasitica.…”

Factors influencing Saprolegnia spp. spore numbers in Norwegian salmon hatcheries

“…Scientists have engaged broadly in the problem, both in exploring the general biology of the organism and in the development of strategies to help control the problems it constitutes. Aspects of morphology (Beakes 1982;Hatai, Willoughby & Beakes 1990), genetics (Dieguez-Uribeondo, Cerenius & S€ oderh€ all 1996;Torto-Alalibo et al 2005;Dieguez-Uribeondo et al 2007;Jiang et al 2013; Thoen et al 2015), pathology (Willoughby 1994;Hussein & Hatai 2002;Thoen et al 2011;Songe et al 2015) and immunology (Alvarez et al 1988(Alvarez et al , 1995Belmonte et al 2014) are described in the literature. Further, a number of prospective fungicides have been investigated for efficacy against saprolegniosis (Hussein et al 2000;Stueland, Heier & Skaar 2005;Ali et al 2014a,b;Warrilow et al 2014).…”

Diagnostic tests and their application in the management of soil- and water-borne oomycete pathogen species

“…Composed of sections with sequences of nucleotides that are highly conserved between species, interspersed with distinctly variable sections, the ITS region has lent itself to the development of sensitive generic primer sets capable of reliably selecting lengths of representative sequence with high variability between species, allowing PCR‐based detection and diagnosis of target oomycetes in complex environmental samples (Klemsdal et al , ; Lees et al , ). These processes have been successfully applied to develop molecular probes which are able to discriminate and measure many important pathogenic oomycete species in both crops and fish stocks (Cooke et al , ; Lévesque & De Cock, ; Tuffs & Oidtmann, ; Beakes et al , ; Songe et al , ). Other regions of the genome are also of use and have been sequenced to reveal nucleotide base pair differences for the phylogenetic characterisation of Phytophthora and Pythium species.…”