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

Abstract

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/mm(2), 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 (H(r)), zeta potentials (P(z)), and subtilisin-like protease (Pr1) activities (A(p)) of these isolates showed the same trends in the three host passages (N: 0-3). In multivariate correlation, the variables N, H(r) and P(z) were found contributing 89% to the mortality variation (r(2)=0.89). Significant positive correlations were also found between H(r) and N (r(2)=0.64), P(z) and N (r(2)=0.52), A(p) and N (r(2)=0.51), H(r) and A(p) (r(2)=0.45), and P(z) and A(p) (r(2)=0.57), respectively. However, irregular changes of H(r) and P(z) 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 H(r) and P(z) associated with cuticle adhesion reflect the heterologous host-induced adaptation and help to select fungal candidates against N. lugens from repeated in vivo passages.