In this study, the supernatant extract
from fermentation broth
of Streptomyces sp. NEAU-H3 showed
strong antifungal activity against Fusarium graminearum strain PH-1 in vitro and in vivo. Three known pyranonaphthoquinones were isolated by means of an
activity-guided method, and frenolicin B was characterized as the
main active ingredient. Frenolicin B displayed strong antifungal activity
against F. graminearum strain PH-1
with an EC50 value of 0.51 mg/L, which is lower than that
of carbendazim (0.78 mg/L) but higher than that of phenamacril (0.18
mg/L). Frenolicin B could also strongly inhibit the mycelial growth
of Fusarium species, including F. graminearum and F. asiaticum, as well as carbendazim-resistant Fusarium strains isolated from field, with EC50 values of 0.25–0.92
mg/L. Results from field experiments showed that the efficacy of frenolicin
B in controlling Fusarium head blight
at a treatment concentration of 75 g ai/ha was better than those of
phenamacril (375 g ai/ha) and carbendazim (600 g ai/ha) or had no
significant difference with that of phenamacril (375 g ai/ha) in 2
years. Scanning electron microscope and transmission electron microscope
observations revealed that after treating F. graminearum mycelia with frenolicin B, the mycelia appeared aberrant and had
an uneven thickness and swelling, the cytoplasm had disintegrated,
and some cell contents were lost. Transcriptome analysis suggests
that frenolicin B might inhibit the metabolism of nucleotides and
energy by affecting genes involved in phosphorus utilization but did
not affect the expression of myosin 5, which is the specific target
of phenamacril. These findings indicate that frenolicin B may be a
potential agrochemical fungicide for controlling Fusarium head blight.