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One hundred and twenty-one single-spore strains of Botrytis cinereaisolated from Bordeaux vineyards were molecularly characterized as either transposaor vacuma, two subpopulations of B. cinereadistinguished by the presence of transposable elements. Forty-three vacumaand 68 transposastrains were distributed into two main classes (mycelial or sclerotial) by morphological phenotype according to the organ of origin. Strains isolated from overwintering sclerotia produced exclusively sclerotial colonies. The mycelial growth rate of 21 transposaand 13 vacumastrains was significantly influenced by agar-medium and temperature. The mycelial growth rate was significantly strain-dependent at favourable temperatures (15, 20 and 25 °C), but not at limiting ones (5 and 28 °C): vacumastrains showed the fastest growth rates. The strains of the two subpopulations were similar in virulence on both host species tested (Vitis viniferaand Nicotiana clevelandii). The grapevine leaves were significantly more susceptible to B. cinereathan those of tobacco. A significant negative correlation was established between virulence and mycelial growth rate. The epidemiological consequences concerning population structure of B. cinereain vineyards are discussed.

The value of BIS for blossom blight risk assessment was studied from data collected in an experimental orchard in south-west France. Trees observed included mature commercial pear and apple trees and some young trees in experimental plots. There was a weather station in the orchard and beehives were present. Field records included flowering times of the pear and apple cultivars studied (mostly Passe-Crassane and Beurré Hardy, Royal Gala and Golden Delicious) and dates when blossom blight was first seen on each cultivar. Between 1980 and 1991, records of blight were available for 25 cases. In most cases, one or more infection risk (IR) days, as defined for BIS, could be found during bloom. DD13 mean sums (sums of degree days above a mean temperature of 13 °C) gave good guidance on times when early signs of blossom blight were present in 14 cases. There was only a slight divergence from BIS guides in a further five cases. Possible reasons for divergence and for non-fit in the remaining six cases are discussed. It is concluded from this study that BIS should give useful guidance on optimal times for protective spray applications and for timing of searches for signs of early blossom blight in south-west of France. Graphical presentations of data provide additional information.

A collection of 127 strains of Erwinia amylovora, the causative agent of fire blight, was tested by PCR amplification of a fragment of the plasmid pEA29. A variability in the length of the DNA fragment obtained was observed after digestion by MspI and Sau3A restriction enzymes. Strains were distributed into three groups according to the length of the DNA product. Most of the strains analysed were placed into two groups. Thirteen strains were clustered into a third group which was linked with the geographical origin of strains: they were all isolates from recently reported outbreaks of fire blight in Austria and in southern Bavaria in Germany. The variation in the length of the amplified fragment is probably due to an insertion into this fragment.