Abstract. The effects of host biodiversity on disease risk may vary greatly depending on host population structure and climatic conditions. Agricultural diseases such as potato late blight, caused by Phytophthora infestans, provide the opportunity to study the effects of intraspecific host diversity that is relatively well-defined in terms of disease resistance phenotypes and may have functional impacts on disease levels. When these systems are present across a climatic gradient, it is also possible to study how season length and conduciveness of the environment to disease may influence the effects of host diversity on disease risk. We developed a simple model of epidemic progress to evaluate the effects on disease risk of season length, environmental disease conduciveness, and host functional divergence for mixtures of a susceptible host and a host with some resistance. Differences in disease levels for the susceptible vs. resistant genotypes shifted over time, with the divergence in disease levels first increasing and then decreasing. Disease reductions from host diversity were greatest for high host divergence and combinations of environmental disease conduciveness and season length that led to moderate disease severity. We also compared the effects of host functional divergence on potato late-blight risk in Ecuador (long seasons), two sites in Peru (intermediate seasons) in El Niño and La Niña years, and the United States (short seasons). There was some evidence for greater disease risk reduction from host diversity where seasons were shorter, probably because of lower regional inoculum loads. There was strong evidence for greater disease reduction when host functional divergence was greater. These results indicate that consideration of season length, environmental conduciveness to disease, and host functional divergence can help to explain the variability in disease response to host diversity.

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SummaryComposition of laurel leaf volatile oil from different geographical origins was studied by means of gas-liquid chromatography, column chromatography and coupled gas chromatography-mass spectrometry. The 37 most important constituents were identified and quantified. Organoleptic quality of Albanian laurel leaf oil was found to be superior to that of samples from France, Italy and Spain.

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SummaryBatch and continuous solvent extraction methods were evaluated, using an alcoholic model system, to select the best alternative for the isolation of volatile aroma compounds from distilled alcoholic beverages. Recoveries using pentane, pentane-diethyl ether (2 : 1) and dichloromethane were compared. Pentane extraction produced the best results, particularly by a continuous procedure for 6 h. Zusammenfassung Vergleich von Extraktionsmethoden fur die Isolierung fliichtiger Verbindungen aus destillierten alkoholischen GetrankenUnter Verwendung eines alkoholischen Modellsystems wurden diskontinuierliche und kontinuierliche Losungsextraktionsmethoden bewertet, um die beste Alternative fur die Isolierung fluchtiger Aromastoffe aus destillierten alkoholischen Getranken zu finden. Es wurden die Wiederfindungswerte bei Verwendung von Pentan, Pentan-Diethylether (2 : 1) und Dichlormethan verglichen. Die Pentanextraktion fiihrte zu den besten Ergebnissen, besonders bei 6std. kontinuierlicher Extraktion.