Aspergillus nidulans was shown to be xerotolerant, with optimal radial growth on basal medium amended with 0.5 M NaCl (osmotic potential [*,] of medium, -3 MPa), 50% optimal growth on medium amended with 1.6 M NaCl (*s of medium, -8.7 MPa), and little growth on medium amended with 3.4 M NaCl (*, of medium, -21 MPa). The intracellular content of soluble carbohydrates and of selected cations was measured after growth on basal medium, on this medium osmotically amended with NaCl, KCI, glucose, or glycerol, and also after hyperosmotic and hypoosmotic transfer. The results implicate glycerol and erythritol as the major osmoregulatory solutes. They both accumulated during growth on osmotically amended media, as well as after hyperosmotic transfer, except on glycerol-amended media, in which erythritol did not accumulate. Furthermore, they both decreased in amount after hypoosmotic transfer. With the exception of glycerol, the extracellular osmotic solute did not accumulate intracellularly when mycelium was grown in osmotically amended media, but it accumulated after hyperosmotic transfer. It was concluded that the extracellular solute usually plays only a transient role in osmotic adaptation. The intracellular content of soluble carbohydrates and cations measured could reasonably account for the intracellular osmotic potential of mycelium growing on osmotically amended media.The ability of microorganisms to grow under conditions of low osmotic (solute) potential has received considerable attention (5, 6, 10). For microorganisms with a cell wall, it is accepted that for active growth the internal water potential must be slightly lower than that external to the cell, so that water will tend to flow into the cell and generate the turgor potential needed for growth. For such microorganisms to grow under conditions of low osmotic potential, this low internal potential is generated largely by the intracellular accumulation of one or more low-molecular-weight solutes or osmoregulators. Although any solute will contribute to the water potential, only a restricted group, the so-called compatible solutes, can accumulate to high concentrations without interfering with enzyme activity and intracellular metabolism.We became interested in the mechanisms whereby ascomycetous filamentous fungi adapt to osmotic stress after we found, with three species, that most mutants resistant to the dicarboximide group of agricultural fungicides are abnormally sensitive to low osmotic potential (3). Because the mode of action of the dicarboximides, which include iprodione, procymidone, and vinclozolin, is not yet known (4), it was anticipated that an understanding of how these fungi adapt to osmotic stress would aid studies of their mode of action. Little data are available on osmotic adaptation in the ascomycetous fungi, although recent studies implicate glycerol as the major osmoregulator in this group (9,12,18,19). In this study, we report on osmotic adaptation in a wild-type strain of the fungus Aspergillus nidulans. MATERIALS AND METHODSOrgan...

In a survey of New Zealand vineyards at harvest 1985, isolates of Botrytis cinerea resistant to benzimidazole and to dicarboximide fungicides were common. The mean frequency of resistance in the major vine-growing districts ranged from 8 to 41% for benzimidazoles. and from 51 to 59% for dicarboximides. All benzimidazole-resistant isolates showed high levels of resistance (EC50 greater than 100 mg/l carbendazim based on radial growth response), and all dicarboximide-resistant isolates showed low levels of resistance. Two subgroups of dicarboximide-resistant isolates were recognized, distinguished in the first instance by their osmotic response. Low-level resistant isolates, which formed a dense margin on osmotically amended medium, exhibited an EC50 for mycelial growth on iprodione of c. 3-2 mg/l; ultra-low-level resistant isolates, which formed a fibrillose margin on osmotically amended medium identical to that of sensitive isolates, exhibited an EC50 of c. 1-B mg/l. In agar culture, radial growth rate, and conidial and sclerotial production of both subgroups were similar to those of sensitive isolates. Virulence (lesion size) and conidial production on grape berries were highest in sensitive isolates, intermediate in ultra-low-level dicarboximide-resistant isolates, and lowest in low-level dicarboximide-resistant isolates. Evidence is presented indicating that ultra-low-level dicarboximideresistant strains have progressively replaced low-level dicarboximide-resistant strains in the vineyard population. The presence of dicarboximide-resistant strains was linked with a partial loss of fungicide efficacy.

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Changes in the proportion of dicarboximide‐resistant strains of Botrytis cinerea were monitored in two vineyard trials conducted during the period from October 1985 to November 1987. Dicarboximide resistance frequency in samples taken prior to flowering from wood (dead cane‐ends, dead tendrils, old bunch remains) was high (66%) in the first trial, and low (12%) in the second trial. In treatments where resistance frequency was high on wood in spring, it decreased during the phase of disease establishment in new bunches irrespective of whether or not dicarboximide fungicides were applied. In the absence of dicarboximide applications, resistance frequency showed little change during the phase of disease development in bunches. The resistance frequency increased, however, if dicarboximide fungicides were applied, the extent of increase depending on the number and timing of applications and on disease severity at the time of application. Where resistance frequency was high on the wood at harvest, it decreased over the following winter but increased again in spring even though no dicarboximides had been applied. The best disease control in both trials was obtained with a programme in which dicarboximide fungicides were only applied during the period from veraison until harvest.