In vitro activity of sorgum seed antifungal proteins against grain mold pathogens

Several sorghum seed antifungal proteins (AFP), including sormatin, chitinase, glucanase, and ribosome-inhibiting protein (RIP), were extracted, partially purified using sequential ammonium sulfate precipitation, and eluted from a CM-Sephadex column using a linear salt gradient. fluted fractions were tested for bioactivity against Fusarium moniliforme, Curvularia lunata, and Aspergillus flavus using hyphal rupture, hyphal extension, and spore germination methods. A fraction containing several AFPs was most inhibitory against F. moniliforme, C. lunata, and A. flavus. Spore germination of all three species was markedly inhibited by 360 ppm of AFPs. The inhibitory effects were not observed when the protein fraction was boiled, suggesting the involvement of undenatured proteins. Hyphal elongation inhibition was the least sensitive assay to detect the inhibitory effects of AFPs on these fungi. F. moniliforme exhibited hyphal rupture at the growing tip at protein levels as low as 70 ppm. C. lunata required higher protein levels (70-360 ppm) and ruptured only at hyphal tips. A. flavus did not exhibit hyphal disruption when treated with AFPs.