Factor analysis of fluctuation in populations ofPseudomonas syringae pv.savastanoi on the phylloplane of the olive

Abstract

Populations ofPseudomonas syringae pv.savastanoi on the surface of olive leaves were monitored quarterly from 1974 to 1981. Seven microbiological parameters were measured: the density of the bacteria on the leaves unfolded in March, in June, and in September; the density of the bacteria on random leaves; the mean vigor of bacterial isolates obtained at each sampling time; and the similarity between the isolates, based on both the simple matching coefficient and the pattern coefficient. Seven environmental parameters were also recorded: the mean temperature, the rainfall, and the frequency and velocity of east and west winds during a period of 30 days before each sampling; the rate of turnover of the leaves during the same period; the number of pollen grains on the leaves at the time of sampling; and the 5-day biochemical oxygen demand of the wash water of leaves in each sample. Factor analysis led to extraction of 7 factors that accounted for 70.69%–92.80% of the maximum variance of every microbiological parameter and 68.92%–96.62% of the maximum variance of every environmental parameter. The factors were identified as “cambial activity”, “leaf age”, “summertime”, “time of blossoming”, “summer rains”, “winter rains”, and “warm weather fronts.” More than 43% of the total parameter variance was loaded in the first 2 factors. Higher communality values (>86% of maximum variance) were obtained for the microbiological parameters based on the distribution of phenotypic characters among the bacterial isolates than for those based on bacterial densities on the phylloplane.