Abstract
Saprolegnia parasitica is recognized as one of the most important oomycetes pests of salmon and trout species. The amplified fragment length polymorphism (AFLP) and method sequence data of the internal transcribed spacer (ITS) were used to study the genetic diversity and relationships of Saprolegnia spp. collected from Canada, Chile, Japan, Norway and Scotland. AFLP analysis of 37 Saprolegnia spp. isolates using six primer combinations gave a total of 163 clear polymorphic bands. Bayesian cluster analysis using genetic similarity divided the isolates into three main groups, suggesting that there are genetic relationships among the isolates. The unweighted pair group method with arithmetic mean (UPGMA) and principal coordinate analysis (PCO) confirmed the pattern of the cluster analyses. ITS analyses of 48 Saprolegnia sequences resulted in five well-defined clades. Analysis of molecular variance (AMOVA) revealed greater variation within countries (91.01%) than among countries (8.99%). We were able to distinguish the Saprolegnia isolates according to their species, ability to produce oogonia with and without long spines on the cysts and their ability to or not to cause mortality in salmonids. AFLP markers and ITS sequencing data obtained in the study, were found to be an efficient tool to characterize the genetic diversity and relationships of Saprolegnia spp. The comparison of AFLP analysis and ITS sequence data using the Mantel test showed a very high and significant correlation (r2 = 0.8317).
Highlights
Saprolegniasis causes great damage and infection in fish in aquaculture and fish farms [1], and Saprolegnia parasitica is recognized as one of the most important oomycetes pests of salmon and trout species in Scandinavia, Chile, Japan, Canada and Scotland [2].it causes losses of tens of millions of dollars in aquaculture businesses worldwide [1].Saprolegnia spp. are generally termed “watermolds” and share common features with both fungi and algae [3]
Twenty-five of the strains have previously been analyzed with respect to their morphological and physiological characteristics [10], and 9 of these strains have been previously characterized with regard to their pathogenicity to Atlantic salmon [10]
Genetic similarity for Saprolegnia isolates using Dice coefficients based on the amplified fragment length polymorphism (AFLP) data ranged from 0.0 to 1.0, with a mean of 0.41
Summary
Saprolegniasis causes great damage and infection in fish in aquaculture and fish farms [1], and Saprolegnia parasitica is recognized as one of the most important oomycetes pests of salmon and trout species in Scandinavia, Chile, Japan, Canada and Scotland [2].it causes losses of tens of millions of dollars in aquaculture businesses worldwide [1].Saprolegnia spp. are generally termed “watermolds” and share common features with both fungi and algae [3]. Saprolegniasis causes great damage and infection in fish in aquaculture and fish farms [1], and Saprolegnia parasitica is recognized as one of the most important oomycetes pests of salmon and trout species in Scandinavia, Chile, Japan, Canada and Scotland [2]. It causes losses of tens of millions of dollars in aquaculture businesses worldwide [1]. All fish and ova in fresh water can possibly be infected by Saprolegnia spp., and the disease is termed saprolegniasis. Differences in pathogenicity have been proved between strains of a Saprolegnia species even within the same taxonomic grouping [7,8,9,10]
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