Preliminary analysis of genetic variability of Metarhizium isolates from Parco del Ticino (Northern Italy)

Abstract: Popillia japonica (Pj) was reported for the first time in Italy and in mainland Europe in 2014. In the infested area, 155 soil samples were collected in 2017 in fields with high infestation rates of Pj larvae to verify the presence of indigenous entomopathogenic fungi. A total of 79 Metarhizium, 7 Beauveria and 7 Paecilomyces isolates were obtained. Eleven Metarhizium isolates were selected based on morphological differences among cultures on PDA medium and analyzed using 15 SSR markers. The isolates (5 M. robertsii, 4 M. brunneum, 1 M. guizhouense, 1 M. lepidiotae) belonged to 9 different genotypes, of which one was shared by 3 M. brunneum isolates. Preliminary virulence tests performed on third instar Pj larvae yielded variable results with efficacy ranging from 34 to 95% mortality. Interestingly, the three isolates of M. brunneum belonging to the same genotype showed different efficacy percentages of 57, 64 and 84%. Furthermore, the two isolates belonging to M. guizhouense and M. lepidiotae revealed lowest efficacy (35% and 34%, respectively) while one isolate of M. brunneum and two of M. robertsii almost reached or exceeded 90%.