Postfire succession of the temporary herbaceous and suffrutescent cover was studied after chaparral fires in San Diego County, California, USA. Four categories of species make up the temporary cover. (I) "Generalized herbaceous perennials" are present before and after fire. Populations of these herbs are sparse under the shrub canopy. They resprout after fire from bulbs or other underground parts and postfire populations are sparse. (2) "Generalized annuals" are present in openings before fire but produce their peak population size in the first few years after fire. (3) Specialized "fire-annuals" are more or less restricted to the 1st postfire yr. (4) Specialized "fire-perennials" (subshrubs) are uncommon before fire, establish from seed in the 1st postfire yr and reach maximum cover in the 3rd and 4th yr.Community-level changes in cover and diversity are interpreted in light of differences in population dynamics of the four groups. Species richness was highest in the 1st yr after fire because this was the only time all four groups were present together. Throughout succession herbaceous species richness was positively related to herb cover, negatively related to elevation and unrelated to slope aspect. The number of annual species fluctuated greatly through succession at all sites, but the number of herbaceous perennials did not. Herb cover fluctuated markedly from year to year and was positively related to amount of annual precipitation and negatively related to subshrub or "fire-perennial" cover.Artificial seeding with annual rye grass Lolium multiflorum had no apparent effect on total herb cover since sites with poor Lolium establishment had as high or higher herb cover as sites with high Lolium establishment. Lolium success was at the expense of the native cover and this negative effect was greatest on the "fire annuals."

The cuticular waxes of a tobacco budworm resistant tobacco, TI-165, contain a series of polar, high molecular weight compounds, which were separated from other components by solvent partitioning and Sephadex LH-20 gel chromatography. Glass capillary gas chromatography (GC-2) of these constituents as trimethylsilyl ethers and GC-2/mass spectrometry indicated that there were six groupings of isomers differing in mass, each from the next by 14 amu. Saponification of the total mixture of compounds yielded sucrose and a series of C2-to C8-aliphatic acids. The major acids were acetic, 2-methylbutyric, and 3-methylvaleric acids. Repeated gel chromatography resulted in the isolation of 6-O-acetyl 2,3,4tri-0-[3-methylvaleryl]-a-D-glucopyranosyl-d-D-fructofuranoside, the major isomer, as defined by NMR and MS data. Other sucrose esters with similar molecular weights were isolated by preparative gas chromatography and saponified, and their acid compositions were determined. Partial hydrolysis of the SE yielded known tetraacylglucopyranosides.

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Leaves of Tobacco Introduction TI-165 were found to be resistant to tobacco budworm [Heliothis virescens (F.)] attack. HPLC profiles of leaf extracts showed that TI-165 had relatively high levels of two components (A and B) that were absent in susceptible varieties. Compounds A and B were isolated from TI-165 by a combination of preparative C18, silicic acid column, and centrifugal thin-layer chromatography. They were identified as diterpene glycosides:  compound A, 16-hydroxygeranyllinalyl-3-O-[α-l-rhamnopyranosyl(1→4)]-β-d-glucopyranoside-16-O-[α-l-rhamnopyranosyl(1→6)]-β-d-glucopyranoside; compound B, 16-hydroxygeranyllinalyl-3-O-[α-l-rhamnopyranosyl(1→4)]-β-d-glucopyranoside-16-O-[α-l-rhamnopyranosyl(1→6)]-[α-l-rhamnopyranosyl(1→4)]-β-d-glucopyranoside (hydroxygeranyllinalool glycosides). Budworm bioassays with whole tobacco leaves and purified mixtures of A and B showed significant correlation between larval weights and levels of A and B. HPLC analyses of freeze-dried leaves of 68 Nicotiana species indicated that 26 species had high levels of diterpene glycosides identical to or related to A and B. Keywords: Nicotiana; Heliothis virescens (F.); antibiosis; 16-hydroxygeranyllinalool glycosides; diterpene glycosides