Variability among isolates of Pseudomonas syringae pv. savastanoi from the phylloplane of the olive.

Leaves of three or four different ages were taken from olive plants quarterly in 1974-1980. One thousand and fifty isolates of Pseudomonas syringae pv. savastanoi from the phylloplane were tested for virulence to the olive and subjected to numerical phenetic analysis using 60 unit characters. The data were analysed using unweighted average linkage (UPGMA) and single linkage clustering on the simple matching (SSM) and pattern (SP) coefficients. The isolates obtained from leaves of a given age at a given time of the year shared higher percentage similarity (S) values between themselves than with the others. Cluster composition was only marginally affected by different coefficients and methods of clustering. UPGMA analysis on the SSM coefficient recovered 92% of the isolates in 10 major clusters at 75% S. Of the isolates from leaves of the same age collected at the same time of the year, 81-99% fell in the same cluster. Conversely, 91-97% of the isolates in five of the major clusters were from leaves of the same type. Of the isolates in the other major clusters, 95-98% were from two different sources but most of the isolates from leaves of one type segregated into discrete subclusters at 85-90% S. Hypothetical median organisms (HMOs) were constructed to represent all the isolates obtained from the leaves of each type each year. The resulting relationships between the HMOs confirmed those described above for the individual isolates.