The third naturally occurring attractant toward zoospores of phytopathogenic Aphanomyces cochlioides from the Spinacia oleracea host plant

A bioassay-guided survey of spinach leaf constituents resulted in 5,4'-dihydroxy-3,3'-dimethoxy-6,7-methylenedioxyflavone being identified as the third naturally-occurring attractant in the host plant toward the zoospores of its pathogen, Aphanomyces cochlioides. The isolate showed attracting activity around Chromosorb W AW particles (60-80 mesh) coated with a 10(-5) M solution in a zoospore suspension. However, this activity was 1/100-1/1000 less than that of cochliophilin A, an attractant in the roots of spinach. Bioassays with the present isolate and related compounds revealed that 5,3',4'-trihydroxy-3-methoxy-6,7-methylenedioxyflavone did not possess attractant activity, but rather weak antagonistic activity toward the former two attractants from spinach.