Bacterial Canker of Stone‐fruits: Iv. Investigation of a Method for Measuring the Inoculum Potential of Cherry Trees

Abstract

Pseudomonas mors‐prunorum Wormald, the organism causing bacterial canker of stone‐fruits, was present on healthy cherry leaves during the autumn in numbers sufficient to suggest that they were the main source of inoculum for the infection of stems and branches. Quantitative estimates of the pathogen could be obtained by shaking leaves in water and plating out the washings. This method was examined in detail as a possible means of comparing the inoculum potentials on different cherry varieties.The numbers of the pathogen varied considerably between leaves and between branches, but not between trees of the same variety. It was estimated that a sample of 192 leaves, eight from each of twenty‐four different branches would be adequate to show differences between varieties if sufficiently replicated in time. The accuracy of a twenty‐four branch sample was tested by comparing parallel samples from two separate groups of trees of the same variety. There was a highly significant correlation between the numbers of bacteria obtained from the two series of samples. From the error variance in an analysis of variance, it was calculated that five successive samples would show a significant difference between two such groups of trees if one exceeded the other by 54%.It was necessary to wash leaves for 4 hr. or more, depending on temperature, to recover all the bacteria from the leaf surfaces. At temperatures lower than 27° C. however, bacterial growth intervened before this stage was reached. At laboratory temperatures a period of 4 hr. washing was found to be most suitable for comparing varieties and gave 80–90% recovery of bacteria without errors due to growth.A characteristic flora of non‐parasitic bacteria was observed on cherry trees, coexisting with the pathogen on the leaf surfaces. The fungus Pullaria pullulans was also extremely abundant.

The Growth of Pseudomonas phaseolicola and Related Plant Pathogens in vivo

“…In this medium Pseudomonas phaseolicola, P. rnorsprunorum and P. syringne all form characteristic radially-striated levan-type colonies (Crosse, 1959) which are readily distinguishable from colonies of contaminant organisms, although in practice tlie latter were rarely encountered.…”

“…There are strong implications here that host specificity in the field may be related to factors controlling in v i m growth of these organisms from very small inocula. I n the field the stone fruit pathogen, Pseudomonas morsprunorum, occurs as an epiphyte on the leaves of its host (Crosse, 1959) and is mobilized in rain to give inoculum which Shanmuganathan (1962) has estimated to vary between lo2 and lo5 bacteria/ml. under optimal disease conditions.…”

Relations between Phage Sensitivity and Virulence in Pseudomonas morsprunorum

“…Bacteria were reisolated from diseased tissues on nutrient agar plus 5 % sucrose (NSA). Pseudomonas rnorsprunorum can be readily identified on this medium by colony characteristics (Crosse, 1959).…”

Structure of the sidechain of lipopolysaccharide from Pseudomonas syringae pv. morsprunorum C28

“…Fill-and-draw culture with harvesting every 24 h was repeated until 50-60 g of dried cells had been amassed. Cultural purity was mo'nitored by streaking out on sucrose-nutrient agar and examining for levan production [6].…”