Entomopathogenic fungi: Are polisporic isolates more pathogenic than monosporic strains?

ANDREAS DEYMIE; CUTHBERTSON, ANDREW; ANDREAS LECLERQUE; VASQUEZ , FABIO; BERNARDO LECHNER; JUAN AGUILERA SAMARITANO; TORRENTE KARINA; CLAUDIA C. LÓPEZ LASTRA

REVISTA DE LA SOCIEDAD ENTOMOLóGICA ARGENTINA

SOCIEDAD ENTOMOLÓGICA ARGENTINA

Lugar: Mendoza; Año: 2017 vol. 76 p. 39 - 43

0373-5680

RESUMEN. Actualmente existen varias cepas de hongos entomopatógenos utilizadas parala fabricación de bio-insecticidas comerciales. Sin embargo, la selección de éstas siguealgunas pautas como la obtención y evaluación de cepas monospóricas (cultivo en masade microorganismos que provienen de una sola espora) Las principales razones para eluso de cultivos monospóricos en lugar de cultivos polispóricos son: la virulencia atenuada ylos posibles ?contaminantes? de la misma especie. En este estudio, diferentes aislamientospolispóricos y sus combinaciones monospóricas se pusieron a prueba para evaluar sueficacia respecto a larvas de Tenebrio molitor (L.) como insecto modelo. Los aislamientospolispóricos de hongos entomopatógenos fueron obtenidos de muestras de suelo deregiones agrícolas áridas. Se seleccionaron cuatro aislamientos polispóricos de Metarhiziumsp. (Metschn.) (CEP413, CEP589, CEP590 y CEP591) para los bioensayos. Se realizaronpruebas de patogenicidad para evaluar la mortalidad en tres tratamientos, Polispóricocompleto (FP), Polispórico parcial (PP) y Monospórico puro (PM). La mortalidad acumuladase midió al día 4 después de la infección. El porcentaje de esporulación se evaluó al día6 después de la infección. La mayor mortalidad se encontró en el tratamiento PF (94%),la menor mortalidad en el día 4 se encontró en PM-CEP413 (32%). Al día 6 el porcentajede esporulación fue mayor en FP (94%) y fue diferente del resto de tratamientos. Elucidardiferentes combinaciones polispóricas y monospóricas para aumentar la eficacia de lasaplicaciones es crucial para ayudar a expandir el uso de bio-insecticidas basados en hongosentomopatógenos.www.biotaxa.org/RSEA. ISSN 1851-7471 (online) Revista de la Sociedad Entomológica Argentina 76 (3-4): 39-43, 2017Copyright AGUILERA SAMMARITANO, J.A. et al.- This is an open access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0) 39PALABRAS CLAVE. Efectividad de cepas. Efectividad de aislamientos. Insecto modelo.Metarhizium sp. Tenebrio molitor.ABSTRACT. Currently only monosporic strains from several entomopathogenic fungi havebeen selected and used for mass production and bioinsecticide manufacturing worldwide.The main reasons for the use of single spore instead of multispore strains are the attenuatedvirulence and the contaminants of the same species. In this study, different polisporic isolatesand their monosporic combinations were tested against Tenebrio molitor (L.) larvae as aninsect model. Isolates were obtained from arid soils. Four Metarhizium sp. (Metschn.)multisporic isolates (CEP413, CEP589, CEP590 and CEP591) were selected for bioassays.Trials were performed to evaluate mortality on three treatments, Full Polisporic (FP), PartialPolisporic (PP) and Pure Monosporic (PM). Cumulative mortality was measured at day 4 postinfection. Sporulation percentage was assessed at day 6 post infection. The highest mortalitywas found at FP treatment (94%), the lowest mortality at day 4 was found at PM-CEP413(32%). At day 6 the sporulation percentage was higher on FP (94%) and it was differentfrom the rest of the treatments. To elucidate different polisporic and monosporic combinationsto improve their effectiveness, may help to expand the use of bioinsecticides based onentomopathogenic fungi.KEYWORDS. Insect model. Isolate effectiveness. Metarhizium sp. Strain effectiveness.Tenebrio molitor.INTRODUCTIONAn epizootic occurs naturally when an unusualnumber of insects have been infected at the same timewithout human intervention (Marcelino, 2007). Epizooticevents produced by entomopathogenic fungi (EF) arerelatively common, and can be important in the naturalregulation of insect populations (Wraight et al., 2007;Skinner et al., 2014). It is well known that some EFspecies (i.e. Metarhizium anisopliae (Metschn.) andBeauveria bassiana (Bals.)) have worldwidedistributions and are often responsible for wide-scaleepizootics (Fuxa, 1987). Although natural epizootics arewell documented (Brandenburg & Kennedy, 1982; Ríos-Velasco et al., 2010; Moura-Mascarin et al., 2016), theinherent biological processes involved in the interactionsbetween the fungal pathogen and the insect pest are notcompletely understood. In their natural state, in whichepizootics are produced, some soil EF like Metarhiziumsp. could act as a multisporic organism rather than amonosporic isolate. Some authors state that ?thewidespread occurrence of asexual reproduction byasexual propagules (conidia) and of hyphalanastomosing can cause confusion because amycelium in its natural environment seems to be a singlephysiological and ecological unit but in reality is agenetic mosaic? (Guarro et al., 1999). It is well knownthat different strains from the same species usuallydisplay great intraspecific variability in respect to theirhost range, pathogenicity, and morphological andphysiological characteristics (Brady, 1979). ?Sexualrecombination, observed in planta and in vitro, could bethe means by which new genetic variants are generatedleading to new biotypes with