ABSTRACT
Little is known about the impact of host immunity on sexual reproduction in fungal pathogens. In particular, it is unclear whether crossing requires both sexual partners to infect living plant tissues. We addressed this issue in a three-year experiment investigating different scenarios of Zymoseptoria tritici crosses according to the virulence ('vir') or avirulence ('avr') of the parents against a qualitative resistance gene. Co-inoculations ('vir × vir', 'avr × vir', 'avr × avr') and single inoculations were performed on a wheat cultivar carrying the Stb16q resistance gene (Cellule) and a susceptible cultivar (Apache), in the greenhouse. We assessed the intensity of asexual reproduction by scoring disease severity, and the intensity of sexual reproduction by counting the ascospores discharged from wheat residues. As expected, disease severity was more intense on Cellule for 'vir × vir' co-inoculations than for 'avr × vir' co-inoculations, with no disease for 'avr × avr'. However, all types of co-inoculation yielded sexual offspring, whether or not the parental strains caused plant symptoms. Parenthood was confirmed by genotyping (SSR markers), and the occurrence of crosses between (co-)inoculated and exogenous strains (other strains from the experiment, or from far away) was determined. We showed that symptomatic asexual infection was not required for a strain to participate in sexual reproduction, and deduced from this result that avirulent strains could be maintained asymptomatically "on" or "in" leaf tissues of plants carrying the corresponding resistant gene for long enough to reproduce sexually. In two of the three years, the intensity of sexual reproduction did not differ between the three types of co-inoculation in Cellule, suggesting that crosses involving avirulent strains are not anecdotal. We discuss the possible mechanisms explaining the maintenance of avirulence in Z. tritici populations and the potential impact of particular resistance deployments such as cultivar mixtures for limiting resistance breakdown.
Subject(s)
Ascomycota , Triticum , Triticum/microbiology , Virulence/genetics , Plant Diseases/genetics , Plant Diseases/microbiology , Ascomycota/geneticsABSTRACT
Resumen Introducción: Enterobacterales productores de carbapenemasas (EPC) son una importante causa de infecciones asociadas a la atención en salud (IAAS). El principal reservorio de EPC lo constituyen pacientes infectados y colonizados, sin embargo, también se han identificado reservorios ambientales. Objetivo: Detectar la presencia de EPC en los sifones de lavamanos de la unidad de cuidados críticos de pacientes quemados adultos (UPC QMD) y unidad de cuidados críticos de pacientes pediátricos crónicos (UCEP). Método: Se recolectaron cuatro muestras de sifones de los lavamanos ubicados en el interior de las unidades de pacientes en UCEP y 10 de UPC QMD. A las muestras se les realizó estudio fenotípico y molecular para detección de carbapenemasas en el Instituto de Salud Pública de Chile. Resultados: En los sifones estudiados de UCEP no se aislaron cepas de EPC. En UPC QMD, 50% de los sifones estudiados se aislaron cepas de EPC. Conclusiones: En UPC QMD se objetivó la presencia de EPC en una alta proporción de los sifones de lavamanos testeados, lo que demuestra un reservorio ambiental de bacterias multi-resistentes.
Abstract Introduction: Carbapenemase-producing Enterobacterales (CPE) are an important cause of health care associated infections (HAI). The main reservoir is constituted by infected and colonized patients; however, environmental reservoirs have also been identified. Objective: To detect the presence of CPE in the sink traps of the critical care unit for adult burn patients (UPC QMD) and the critical care unit for chronic pediatric patients (UCEP). Material and Method: Four samples of trap were collected from the sinks located inside the patient units at PICU and 10 at UPC QMD. The samples underwent a phenotypic and molecular study for the detection of carbapenemases at the Institute of Public Health of Chile. Results: In the UCEP no EPC strains were isolated. In UPC QMD, CPE was detected in 50% of the traps. Conclusions: In UPC QMD, the presence of CPE was observed in a high proportion of the tested sinks traps, which shows an environmental reservoir of multi-resistant bacteria.
ABSTRACT
BACKGROUND: Although the most common path of infection for fire blight, a severe bacterial disease on apple, is via host plant flowers, quantitative trait loci (QTLs) for fire blight resistance to date have exclusively been mapped following shoot inoculation. It is not known whether the same mechanism underlies flower and shoot resistance. RESULTS: We report the detection of a fire blight resistance QTL following independent artificial inoculation of flowers and shoots on two F1 segregating populations derived from crossing resistant Malus ×robusta 5 (Mr5) with susceptible 'Idared' and 'Royal Gala' in experimental orchards in Germany and New Zealand, respectively. QTL mapping of phenotypic datasets from artificial flower inoculation of the 'Idared' × Mr5 population with Erwinia amylovora over several years, and of the 'Royal Gala' × Mr5 population in a single year, revealed a single major QTL controlling floral fire blight resistance on linkage group 3 (LG3) of Mr5. This QTL corresponds to the QTL on LG3 reported previously for the 'Idared' × Mr5 and an 'M9' × Mr5 population following shoot inoculation in the glasshouse. Interval mapping of phenotypic data from shoot inoculations of subsets from both flower resistance populations re-confirmed that the resistance QTL is in the same position on LG3 of Mr5 as that for flower inoculation. These results provide strong evidence that fire blight resistance in Mr5 is controlled by a major QTL on LG3, independently of the mode of infection, rootstock and environment. CONCLUSIONS: This study demonstrates for the first time that resistance to fire blight caused by Erwinia amylovora is independent of the mode of inoculation at least in Malus ×robusta 5.
