In vivo passages of heterologous Beauveria bassiana isolates improve conidial surface properties and pathogenicity to Nilaparvata lugens (Homoptera: Delphacidae)

In entomopathogenic hyphomycetes, desired candidates against the brown planthopper, Nilaparvata lugens (a sap-sucking rice pest in Asia), are lacking. In this study, 21 Beauveria bassiana isolates from heterologous host insects showed low pathogenicity to third-instar nymphs sprayed at the high concentration of ∼1000 conidia/mm2, causing only 2–23% mortalities. Of those, three isolates killed significantly more nymphs (up to 45–62%) after two in vivo passages but no more after further passage. Conidial hydrophobicity rates (Hr), zeta potentials (Pz), and subtilisin-like protease (Pr1) activities (Ap) of these isolates showed the same trends in the three host passages (N: 0–3). In multivariate correlation, the variables N, Hr and Pz were found contributing 89% to the mortality variation (r2 = 0.89). Significant positive correlations were also found between Hr and N (r2 = 0.64), Pz and N (r2 = 0.52), Ap and N (r2 = 0.51), Hr and Ap (r2 = 0.45), and Pz and Ap (r2 = 0.57), respectively. However, irregular changes of Hr and Pz occurred in four other isolates, whose pathogenicity to N. lugens was not enhanced by repeated host passages, resulting in no correlation between the variables. Our data indicate that the conidial surface properties Hr and Pz associated with cuticle adhesion reflect the heterologous host-induced adaptation and help to select fungal candidates against N. lugens from repeated in vivo passages.

Graphical abstractPathogenicity and phenotypic changes of Beauveria bassiana after in vivo passages.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► In vivo passages of three heterologous Beauveria bassiana isolates significantly enhance brown planthopper mortalities. ► The enhanced mortalities are associated with the increases of conidial hydrophobicity and zeta potential in the passages. ► The improved surface properties are associated with the increased activities of subtilisin-like proteases (Pr1) in conidia.