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The accuracy of host range testing in weed biocontrol programmes using plant pathogens has been questioned prompting a research programme into the field safety record of pathogens used for weed biocontrol in New Zealand Nationwide disease surveys were conducted from 20002009 and focused on species closely related to target weeds and therefore potentially most at risk of attack These surveys identified pathogens associated with any disease symptoms observed on nontarget hosts Disease damage attributable to biocontrol agents was observed on two nontarget plants Pustules of the blackberry rust Phragmidium violaceum were found on the endemic Rubus species R cissoides (bush lawyer tataramoa) at one location This result was predicted from host range safety tests conducted prior to its arrival in New Zealand No nontarget damage was observed in the remaining case studies confirming to date that all biocontrol pathogens are highly host specific to their target weeds

Reactions of nine olive cultivars inoculated with olive or oleander strains of Pseudomonas savastanoi were evaluated under glasshouse conditions. Two quantitative indices of pathogenicity were used: 1. gall size from standardised inoculations, measured after 2 months; 2. rate of change of gall size with increasing inoculum concentration. These two indices were combined in a single plot that appears to give the best resolution of all data. Responses of olive cultivars to olive strains of P. savastanoi suggest that cultivars Carolea, Koroneiki, Leccino and Pendolino are the most tolerant, and that Barnea, Manzanillo, Picholine, Picual and a South Australian selection of Verdale are the least tolerant. Olive and oleander strains of P. savastanoi differed in virulence, and between-plant variability in reaction to inoculation was noted. Hypersensitive reactions do not appear to be part of mechanisms of tolerance. Olive strains of P. savastanoi affected all cultivars more severely than did equivalent inoculations with oleander strains.