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 ofP. tabacina sporangia, the tobacco blue mold pathogen, and to a lesser extentAlternaria alternata, the tobacco brown spot pathogen. Exposure to 10 μg/cm(2) of α- and β-duvatrienemonols, sucrose esters, or hydrocarbons did not inhibit germination, whereas germination was significantly decreased bycis-abienol.cis-Abienol did not inhibit sporangial germination when combined with sucrose esters or hydrocarbons at a combined 10 μg/cm(2). 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/cm(2) resulted in a small but significant stimulation of germination. Previously, the DVT-diols had been identified only as inhibitory toP. tabacina. None of the leaf surface chemicals affected germination ofA. alternata conidia.

Witchweed (Striga asiatica L. Kuntze) seeds were incubated at 28 C in a moist environment for a 14‐day period, after which seeds germinated only when exposed to specific natural or synthetic germination stimulants. Changes in lipid composition were determined during germination of witchweed seeds and during early seedling growth. Witchweed seeds contained 37.5% (w/w) oil. Increased levels of monogalactosyl‐diacylglycerol and phosphatidylglycerol suggested the enlargement or multiplication of plastids after witchweed seeds had germinated. In contrast to the usual course of events in seeds with high oil reserves, witchweed seeds did not hydrolyze triacylglycerol rapidly during or after germination. These findings indicated that triacylglycerol in germinating witchweed seeds was conserved for subsequent use during haustorial formation and host invasion.