Hydrophobicity-Related Protein Contents and Surface Areas of Aerial Conidia are Useful Traits for Formulation Design of Fungal Biocontrol Agents

Abstract

To clarify the potential use of hydrophobicity-related traits of aerial conidia in formulation design of fungal biocontrol agents, hydrophobicity rates (H (r)) and surface areas (S (a)) of aerial conidia were assessed with 48 strains of Beauveria bassiana, Isaria fumosorosea and Metarhizium spp. Inter- or intra-specific variation was large in H (r) (59.7-92.2%) and S (a) (7.9-25.3 microm(2) conidium(-1)) measurements, which were significantly correlated (r (2) = 0.55). Six isolates of the three fungi with distinguished H (r) and S (a) were further studied. Conidial wall proteins of these isolates were sequentially extracted with sodium dodecyl sulfate (SDS), formic acid (FA) and trifluoroacetic acid (TFA). Their H (r) values were significantly correlated to the contents (P (c)) of TFA-soluble, but FA-insoluble, proteins (2.7-44.8 microg per 10(7) conidia; r (2) = 0.79) and reduced drastically by the FA/TFA treatments, which eliminated the hydrophobin-based rodlet layers of conidial surfaces. However, the SDS treatments had no effect on either H (r) or rodlet layers. The dispersancy of a tested emulsifier to oil formulations of the six isolates in water was adversely correlated to their H (r) (r (2) = 0.94). The results indicate that both P (c) and S (a) are inherent hydrophobicity-related traits and can be utilized to select fungal biocontrol candidates for improved formulation and application.