Diketopiperazine cyclo(-l-Leu-l-Phe) with plant elicitation activity and anti-oomycete activity against Plasmopara viticola.

The aim of this study was to contribute to the reduction of synthetic chemical fungicide application in viticulture by using cyclo(-l-Leu-l-Phe) (cLF) produced by Bacillus subtilis KS1, a candidate for biological control agent. cLF is a diketopiperazine and belongs to the family of 2,5-diketopiperazines. KS1 secreted micromolar levels of cLF into culture medium. Micromolar concentrations of cLF structure-dependently decreased by ∼90% both disease severity and lesion density of downy mildew in grapevine cultivated in a growth chamber. Microscopic observation demonstrated that cLF inhibited Plasmopara viticola haustorium formation by 80% but not zoospore germination on leas disks. Interestingly, millimolar concentrations of cLF induced plant defense response, such as expression of genes encoding chitinase and β-1,3-glucanase, in grapevine leaves through the salicylic acid and jasmonate signaling pathways. We demonstrated that cLF was a weapon against P. viticola infection. Further evaluation of cLF in field trials is required to uncover its inherent characteristics.