INFLUENCE OF TOBACCO LEAF SURFACE CHEMICALS ON GERMINATION OF PERONOSPORA-TABACINA ADAM SPORANGIA

Chromatographic procedures were utilized to isolate and purify components of tobacco cuticular extracts and leaf surface chemicals. In vitro microbial bioassays determined the influence of these leaf surface compounds on germination and germ tube morphology of P. tabacina sporangia, the tobacco blue mold pathogen, and to a lesser extent Alternaria alternata, the tobacco brown spot pathogen. Exposure to 10 μg/cm2 of α- and β-duvatrienemonols, sucrose esters, or hydrocarbons did not inhibit germination, whereas germination was significantly decreased by cis-abienol. cis-Abienol did not inhibit sporangial germination when combined with sucrose esters or hydrocarbons at a combined 10 μg/cm2. Germination of sporangia was completely inhibited by α- and β-duvatrienediols. In contrast to a previous report, α-DVT-diol was more inhibitory than the β isomer. Toxic effects of the DVT-diols were not altered by pH. Diluting the DVT-diols to less than 0.1 μg/cm2 resulted in a small but significant stimulation of germination. Previously, the DVT-diols had been identified only as inhibitory to P. tabacina. None of the leaf surface chemicals affected germination of A. alternata conidia. © 1990 Plenum Publishing Corporation.