Mixing of propagules from discrete sources at long distance: comparing a dispersal tail to an exponential

Background  

Rare long distance dispersal events impact the demography and the genetic structure of populations. When dispersal is modelled via a dispersal kernel, one possible characterisation of long-distance dispersal is given by the shape of the tail of the kernel, i.e. its type of decay. This characteristic is known to directly act on the speed and pattern of colonization, and on the spatial structure of genetic diversity during colonization. In particular, colonization waves behave differently depending on whether the kernel decreases faster or slower than an exponential (i.e. is thin-tailed vs. fat-tailed). To interpret and extend published results on the impact of long-distance dispersal on the genetic structure of populations, we examine a classification of dispersal kernels based on the shape of their tails and formally demonstrate qualitative differences among them that can influence the predicted diversity of a propagule pool sampled far from two distinct sources.     

The corky root rot pathogen Pyrenochaeta lycopersici secretes a proteinaceous inducer of cell death affecting host plants differentially

Pathogenic isolates of Pyrenochaeta lycopersici, the causal agent of corky root rot of tomato, secrete cell death in tomato 1 (CDiT1), a homodimeric protein of 35 kDa inducing cell death after infiltration into the leaf apoplast of tomato. CDiT1 was purified by fast protein liquid chromatography, characterized by mass spectrometry and cDNA cloning. Its activity was confirmed after infiltration of an affinity-purified recombinant fusion of the protein with a C-terminal polyhistidine tag. CDiT1 is highly expressed during tomato root infection compared with axenic culture, and has a putative ortholog in other pathogenic Pleosporales species producing proteinaceous toxins that contribute to virulence. Infiltration of CDiT1 into leaves of other plants susceptible to P. lycopersici revealed that the protein affects them differentially. All varieties of cultivated tomato (Solanum lycopersicum) tested were more sensitive to CDiT1 than those of currant tomato (S. pimpinellifolium). Root infection assays showed that varieties of currant tomato are also significantly less prone to intracellular colonization of their root cells by hyphae of P. lycopersici than varieties of cultivated tomato. Therefore, secretion of this novel type of inducer of cell death during penetration of the fungus inside root cells might favor infection of host species that are highly sensitive to this molecule.     

Landscape ecology: Population genetics at the metapopulation level

Distribution of genetic diversity in a landscape depends on both within and among population processes. Selective pressures within populations have traditionally been studied by population genetics, which usually assumes that populations are at equilibrium. However, when selection pressures within and among populations are different, landscape processes are required to define an equilibrium (landscape being defined as the habitat of a set of populations called a metapopulation, and populations will differ depending on their situation in the landscape, i.e. their age and the state of neighboring populations). We examine reproduction systems and life history traits, for which variation depends on landscape processes. Predictions of their states in a metapopulation are drawn from theoretical models, and confronted to observations collected in natural populations.     

The corky root rot pathogen Pyrenochaeta lycopersici manipulates tomato roots with molecules secreted early during their interaction

Abstract

Corky root rot is a ubiquitous soil-borne disease of tomato caused by the pathogen Pyrenochaeta lycopersici. This filamentous fungus is found on the roots of many crops and can persist in the soil up to 15 years as microsclerotia. High prevalence of corky root rot can be partly explained by the endurance and the broad host range of P. lycopersici, but how this fungus can gain access to host roots is still poorly understood, as its competitive saprophytic ability is very low. We have combined microscopy and reporter gene techniques to investigate the tomato–P. lycopersici interaction in vitro, and discovered the pathogen secretes molecules that change the direction of root growth and induce cell necrosis specifically in the apical part of the root of tomato (apex, elongation zone and beginning of the root hair zone). Moreover, we found that the fungus preferentially infects immature root cells that are sensitive to these secreted fungal molecules, whereas infection is blocked in mature and insensitive parts of the root. Our study sheds light on novel and important features of the biology of this pathogen, which could contribute to its fitness in the rhizosphere.     

Control of cutaneous mycosis in five chimpanzees (Pan troglodytes) with lufenuron

Five chimpanzees at the Limbe Wildlife Centre in Cameroon, of both sexes and between six and eight years of age, were treated with lufenuron at a dose rate of 60 mg/kg bodyweight to control various types of mycotic skin infections. The 409.8 mg tablets were administered by mixing them with milk and avocado. Each animal received two or three treatments three weeks apart. Most of them improved significantly during the two to three weeks after the first treatment, and they had completely recovered two to four months later. All the chimpanzees accepted the medication readily, and no adverse drug reactions were observed either immediately after the treatment or during the subsequent eight to 10 months.     

Inheritance of resistance to carboxylic acid amide (CAA) fungicides in Plasmopara viticola

Mandipropamid is a new mandelic acid amide fungicide expressing high activity against foliar infecting oomycetes, including the grapevine downy mildew, Plasmopara viticola . Because cross-resistance with the valinamide fungicides iprovalicarb and benthiavalicarb and the cinnamic acid amide fungicides dimethomorph and flumorph was postulated, all five compounds are classified as carboxylic acid amide (CAA) fungicides. To support this classification, cross-resistance among these compounds with field isolates and the segregation of resistance in F₁ and F₂ progeny of P. viticola were evaluated. A bimodal distribution of sensitivity in field isolates and cross-resistance among all CAAs for the vast majority of isolates were detected. Crosses between sensitive (s) and CAA-resistant (r) isolates of opposite mating types, P1 and P2, yielded abundant oospores. All F₁-progeny isolates were sensitive to CAAs (s:r segregation 1:0), whereas in F₂ progeny segregation of about 9:1 (s:r) was observed suggesting that resistance to CAA fungicides is controlled by two recessive nuclear genes. Mating type segregated in a ratio P1:P2 of c . 2:1 in F₁ and 1:1 in F₂ progeny. In the same crosses, resistance to the phenylamide fungicide mefenoxam segregated in a ratio of c . 1:3:2 (sensitive:intermediate:resistant), reflecting the monogenic, semidominant nature of resistance. The risk of resistance in P. viticola was classified as high for phenylamide and moderate for CAA fungicides. This is the first report on the inheritance of phenotypic traits in P. viticola .