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In 2000, 137 strains of Botrytis cinerea were isolated from different plant hosts worldwide. The isolates had not been exposed to boscalid and were therefore suitable to establish a baseline sensitivity. In order to determine the sensitivity of these isolates, an appropriate microtiter assay was developed. YBA-medium was the medium of choice, as it allowed sufficient growth but did not lead to false positive results. ED50-values ranged from 0.01 to 0.21 ppm, the ED98-values from 0.1 to 2.21 ppm. No growth was observed at concentrations >3 ppm.

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Two new isochromans named pseudoanguillosporin A (2a) and B (3), together with the known cephalochromin (1), were isolated from Pseudoanguillospora sp. The C‐2 absolute configuration of 2a and 3 was deduced from its CD spectrum by the isochroman helicity rule, supported by TDDFT CD calculations. The absolute configuration of the sec‐hydroxyl group of 3 was determined by the Mosher NMR method from the MPA esters of its methylated derivative. The axial chirality of 1 was assigned through exciton analysis of its CD spectrum and confirmed by ZINDO CD calculations. The metabolites showed broad antimicrobial activities.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Treatments with prohexadione-calcium led to lowered incidence of fire blight, scab and other diseases in pome fruit trees and other crop plants. In addition to acting as a growth regulator, prohexadione-calcium interferes with flavonoid metabolism and induces the accumulation of the 3-deoxycatechin luteoliflavan in shoots of pome fruit trees. Luteoliflavan does not possess any remarkable antimicrobial activity. Therefore luteoforol, its unstable and highly reactive precursor, has been tested in vitro for its bactericidal and fungicidal activities. Luteoforol was found to be highly active against different strains of Erwinia amylovora, the causal agent of fire blight, and all other bacterial and fungal organisms tested. Phytotoxic effects were also observed in pear plantlets. The results obtained indicate that prohexadione-calcium induces luteoforol as an active principle with non-specific biocidal properties. It is proposed that luteoforol is released upon pathogen attack from its cellular compartment and inhibits further disease development by destroying pathogen cells as well as by inducing a hypersensitive-like reaction in the host plant tissue. This mechanism would be closely analogous to the one known for structurally related phytoalexins in sorghum.Abbreviations: FHT -flavanone 3-hydroxylase; ProCa -prohexadione-calcium; TrixE -trinexapac-ethyl.