Detection of DSF from X. fastidiosa and Xcc strains. (A-D) DSF reporter strain 8523 (pKLN55) grown to the left of concentrated X. fastidiosa culture extracts of the wild-type strain Temecula (A), sterile medium (B), or rpfF mutant strains KLN61 (C) and KLN62 (D). (E-I) Strain 8523 (pKLN55) sprayed over colonies of Xcc strain 8004 (wild-type, E), strain 8523 (rpfF, F), Xcc rpfF rescue strain 8523 (pKLN69) (G), X. fastidiosa rpfF rescue strain 8523 (pKLN70) (H), empty vector control strain 8523 (pBBR1MCS-3) (I). Green fluorescence indicates detection of DSF that has diffused from the culture extract or colony.