The ontogeny of perithecia in Guignardia bidwellii

International audienceThe ontogeny of perithecia in Guignardia bidwellii was studied with contaminated berries and under in vitro conditions. The first developmental stage consists of a stromatic envelope surrounding a carpocentrum in which an ascogonial apparatus (composed of ascogonial cells and trichogynes) differentiates at the second stage. Stage 3 is marked by the incipient formation of the ascal locule and development of pseudoparaphyses. At the subadult stage ( = stage 4) these filaments intermingle with asci and they are progressively stretched owing to ascus expansion. The mature ascocarp (stage 5) contains numerous eight-spored asci and opens through an apical ostiole. The developmental features of Guignardia bidwellii indicate a pseudoparaphysate ascolocular type of development. Consequently, the fungus is more correctly placed in the Botryosphaeriaceae than in the Mycosphaerellaceae

Population genetics in the homothallic lichen-forming ascomycete Xanthoria parietina

The genetic diversity within and among populations of Xanthoria parietina was studied at the subspecific level with a fingerprinting technique (RAPD-PCR) applied to sterile cultured multispore isolates, each being derived from a single apothecium. Populations from coastal, rural and urban sites from NW, SW and central France and from NE Switzerland were investigated. Between 1 and 8 microsites of a few decimetres square, each comprising 13 to 27 thalli of X. parietina, were analysed per population. A total of 132 isolates from epiphytic and 3 isolates from epilithic specimens were investigated. Phenotypic variation was recorded among some of the thalli in the field and among sterile cultured isolates in the laboratory. A high diversity of genotypes was observed, even among thalli growing side by side in phenotypically homogenous populations. An average of 73·5 % polymorphism was found in all samples. As shown with Principal Coordinates Analysis (PCO), most of the genetic variation (90%) resided within, not among, populations. As X. parietina had previously been shown with molecular and fingerprinting techniques to be homothallic, the potential genetic background of this diversity is discussed. Intense genotype rather than gene (allele) flow seems to be an important element in X. parietina populations

Les périthèces et les asques du

Les périthèces du Leptosphaeria senegalensis naissent à partir de primordiums de type stromato-glomérulaire. Dans les ébauches, des cellules carpocentrales privilégiées donnent naissance à une ou plusieurs cellules femelles (= ascogones) surmontées chacune d’un court trichogyne unicellulaire ; les ascogones se transforment directement en cellules à dicaryon, sans qu’intervienne une fécondation par trichogamie et sans l’intermédiaire de vésicules pro-sporophytiques. Le développement des parties stériles du périthèce est celui d’un Pyrénomycète ascoloculaire à carpocentre de type Pleospora avec formation d’une garniture périloculaire (ménisque sous-hyménial fugace et cloche sus-hyméniale génératrice de pseudo-paraphyses, mais non de périphyses)

Les périthèces et les asques du

La paroi ascale du Leptosphaeria senegalensis se rattache nettement au type bituniqué ; elle comporte, au stade final, un exoascus et un endoascus séparés par un espace clair ; l’endoascus contient des fibrilles, réparties en trois sous-couches, et dont les plus internes sont plissées en accordéon. Les ascospores ont une paroi complexe comportant, de l’intérieur vers l’extérieur : une endospore, une épispore, plus épaisse autour de la moitié antérieure du corps sporal, une périspore et une ectospore, épaissie en une cupule coiffant l’extrémité postérieure. La comparaison des ascospores de deux Leptosphaeria « vrais » (L. acuta et L. maculans) avec celle du L. senegalensis montre que le rattachement de cette dernière espèce au genre Leptosphaeria n’est pas justifié

La truffe, la terre, la vie

National audienc