Lysobacter capsici AZ78 produces cyclo(L-Pro-L-Tyr), a 2,5-diketopiperazine with toxic activity against sporangia of Phytophthora infestans and Plasmopara viticola

AIMS: To investigate low molecular weight compounds producedin vitrobyLysobacter capsiciAZ78 and their toxic activity against sporangia of plantpathogenic oomycetes. METHODS AND RESULTS: Assays carried outin vitroshowed thatL. capsiciAZ78drastically inhibits the growth of plant pathogenic oomycetes. Accordingly, thepreventive application of culture filtrates ofL. capsiciAZ78 on grapevine andtomato plants reduced the infections, respectively, caused byPlasmopara (Pl.)viticolaandPhytophthora infestans. The subsequent chemical analysis of theculture filtrates ofL. capsiciAZ78 by spectroscopic (essentially 1D and 2D1HNMR and13C NMR and ESI MS spectra) and optical methods led to theidentification of the 2,5-diketopiperazine cyclo(L-Pro-L-Tyr) that inhibited thedevelopment ofP. infestanssporangiain vitroand on tomato leaves.Furthermore, a genomic region with high sequence identity with genes codingfor a hybrid polyketide synthase and nonribosomal peptide synthetase wasdetected inL. capsiciAZ78. CONCLUSIONS: Lysobacter capsiciAZ78 produces cyclo(L-Pro-L-Tyr)in vitrothatwas effective in killing the sporangia ofP. infestansandPl. viticola in vitro.Moreover, this low molecular weight compound prevents the occurrence oflate blight lesions when applied on tomato leaves. SIGNIFICANCE AND IMPACT OF THE STUDY: The application ofL. capsiciAZ78 cellsor its own culture filtrates effectively controls bothP. infestansandPl. viticola.Cyclo(L-Pro-L-Tyr) produced byL. capsiciAZ78 is toxic against sporangia ofboth these oomycetes. These data enforce the potential in the use ofLysobactermembers for the control of plant pathogenic oomycetes and provide the basisfor the development of new low-impact fungicides based on cyclo(L-Pro-L-Tyr).