Orbitides and free polyamines have similarly limited fungicidal activity against three common pathogens of flax in vitro

Fusarium oxysporum f. sp. lini and Septoria linicola are causes of fusarium wilt and pasmo in flax (Linum usitatissimum). Members of a third fungal genus, Alternaria spp., have also been found in fiber and linseed varieties of flax, and are a source of post-harvest spoilage and mycotoxins in a wide range of crops. We performed a microdilution assay and calculated the median effective concentration (EC50) to compare the potency of cyclolinopeptides (CLPs), two polyamines (spermidine and spermine), and the fungicide carbendazimin in the control of three fungi that have potential pathogenic activity (F. oxysporum, S. linicola, and Alternaria spp), of which the first two are particulary significant causes of disease in flax. For carbendazim, all EC50 values were <0.6 mu g/mL. The observed EC50 ranged from 111 to 340 mu g/mL for a mixture of six unique CLPs, 109 to 778 mu g/mL for spermine, and 21 to 272 mu g/mL for spermidine. Spermidine was most effective against Alternaria sp., with an EC50 of 21 mu g/mL. The results presented here showed that polyamines and CLPs possess limited antifungal activities against several fungi, with spermidines the most effective naturally occurring compound tested. Our findings do not support the hypothesis that CLPs act as potent antifungals against the three species of pathogens tested.

Automated summary

The causes of fusarium wilt and pasmo in flax (Linum usitatissimum) are Fusarium oxysporum f. sp. lini and Septoria linicola. Alternaria spp., a third fungal genus, has also been found in flax varieties and is a source of spoiling and mycotoxins in crops. The study compared the effectiveness of cyclolinopeptides (CLPs), polyamines (spermidine and spermine), and the fungicide carbendazimin in controlling three fungi (F. oxysporum, S. linicola, and Alternaria spp). The results showed limited antifungal activities of polyamines and CLPs, with spermidine being the most effective compound.