What if esca disease of grapevine were not a fungal disease?

Esca disease,which attacks the wood of grapevine,has become increasingly devastating during the past three decades and represents today a major concern in all wine-producing countries.This disease is attributed to a group of systematically diverse fungi that are considered to be latent pathogens,however,this has not been conclusively established.This study presents the first in-depth comparison between the mycota of healthy and diseased plants taken from the same vineyard to determine which fungi become invasive when foliar symptoms of esca appear.An unprecedented high fungal diversity,158 species,is here reported exclusively from grapevine wood in a single Swiss vineyard plot.An identical mycota inhabits wood of healthy and diseased adult plants and presumed esca pathogens were widespread and occurred in similar frequencies in both plant types.Pioneer esca-associated fungi are not transmitted from adult to nursery plants through the grafting process.Consequently the presumed esca-associated fungal pathogens are most likely saprobes decaying already senescent or dead wood resulting from intensive pruning,frost or other mecanical injuries as grafting.The cause of esca disease therefore remains elusive and requires well executive scientific study.These results question the assumed pathogenicity of fungi in other diseases of plants or animals where identical mycota are retrieved from both diseased and healthy individuals.

Molecular analysis of the sex chromosomes of the platyfish Xiphophorus maculatus: Towards the identification of a new type of master sexual regulator in vertebrates

In contrast to mammals and birds,fish display an amazing diversity of genetic sex determination systems,with frequent changes during evolution possibly associated with the emergence of new sex chromosomes and sex-determining genes.To better understand the molecular and evolutionary mechanisms driving this diversity,several fish models are studied in parallel.Besides the medaka(Oryzias latipes Temminck and Schlegel,1846)for which the master sex-determination gene has been identified,one of the most advanced models for studying sex determination is the Southern platyfish(Xiphophorus maculatus,Günther 1966).Xiphophorus maculatus belongs to the Poeciliids,a family of live-bearing freshwater fish,including platyfish,swordtails and guppies that perfectly illustrates the diversity of genetic sex-determination mechanisms observed in teleosts.For X.maculatus,bacterial artificial chro-mosome contigs covering the sex-determination region of the X and Y sex chromosomes have been constructed.Initial molecular analysis demonstrated that the sex-determination region is very unstable and frequently undergoes duplications,deletions,inversions and other rearrangements.Eleven gene candidates linked to the master sex-determining gene have been identified,some of them corresponding to pseudogenes.All putative genes are present on both the X and the Y chromosomes,suggesting a poor degree of differentiation and a young evolutionary age for platyfish sex chromosomes.When compared with other fish and tetrapod genomes,syntenies were detected only with autosomes.This observation supports an independent origin of sex chromosomes,not only in different vertebrate lineages but also between different fish species.