No abstract

Endophytes are microorganisms that live inside the plant tissue without causing external symptoms. All plants in nature harbor endophytes. Some endophytes produce and secrete biologically active compounds, known as secondary metabolites, which can help the host plant cope with bacterial, fungal, and other pest pathogens. Endophytes are isolated from aquatic plants and algae. Diseases are detrimental in the aquaculture industry where chemical pesticides and antibiotics are widely used in an attempt to cope with fish pathogens. However, the ability to prevent disease outbreaks in aquaculture is currently extremely limited. Here, we isolated 173 bacterial and fungal endophytes from 16 Mediterranean seaweed and 4 algae from fresh or thermo-mineral water. We found 88 endophytes (51%) with biological activity against four common aquaculture pathogens. Fifty endophytes (29%) caused mortality of at least one of these four pathogens. We identified 23 bioactive endophytes, 18 of which are from the Bacilli class. Our findings suggest that macroalgae from different aquatic environments can serve as a good source of potential biocontrol agents against aquaculture diseases. To the best of our knowledge, there are no published studies demonstrating the use of algal endophytes to control aquaculture diseases. Our study may lead to finding new molecules for use as novel environmentally friendly products that will solve one of the most challenging problems for the growing aquaculture industry: pathogens and pests.

Plant pathogens usually originate and diversify in geographical regions where hosts and pathogens coevolve. Erysiphe necator, the causal agent of grape powdery mildew, is a destructive pathogen of grapevines worldwide. Although Eastern US is considered the centre of origin and diversity of E. necator, previous reports on resistant native wild and domesticated Asian grapevines suggest Asia as another possible origin of the pathogen. By using multi-locus sequencing, microsatellites and a novel application of amplicon sequencing (AmpSeq), we show that the population of E. necator in Israel is composed of three genetic groups: Groups A and B that are common worldwide, and a new group IL, which is genetically differentiated from any known group in Europe and Eastern US. Group IL showed distinguished ecological characteristics: it was dominant on wild and traditional vines (95%); its abundance increased along the season; and was more aggressive than A and B isolates on both wild and domesticated vines. The low genetic diversity within group IL suggests that it has invaded Israel from another origin. Therefore, we suggest that the Israeli E. necator population was founded by at least two invasions, of which one could be from a non-East American source, possibly from Asian origin.