Statistics and Abstract

I've been analysing the data obtained from the experiments last term where I dipped whole plants in inoculum and measured the number of lesions and the area of the lesions on the plant. I have submitted an abstract for a poster to present at one or two meetings this summer.

Phytophthora ramorum - pathogenic fitness of the three clonal lineages

Clare Elliott, Virginia McDonald and Niklaus Grunwald

The Oomycete pathogen Phytophthora ramorum causes sudden oak death on oak and ramorum blight on a wide range of ornamental plants causing severe economic losses to the nursery industry. The US population of P. ramorum consists of three distinct clonal lineages referred to as NA1, NA2, and EU1. The hypothesis of differences in pathogenic fitness among these three lineages was tested through the infection of detached leaves and whole plants in wounded and un-wounded inoculations of Rhododendron. In independent experiments the fitness of isolates within lineages was determined using the fitness components lesion area (LA), sporulation capacity (SC), incubation period (IP_w) and the area under the lesion expansion curve (AULEC) on two cultivars of Rhododendron; the more susceptible cv. R. catawbiense ‘Boursault’ and the moderately resistant cv. ‘Lee’s Dark Purple’. For all wounded detached leaf experiments and for the whole plant work 3 isolates from each clonal lineage were tested, and for the un-wounded detached leaf assay the sample size was increased to 10 isolates per lineage. In the non-wounded whole plant experiments incidence was measured by number of infection points and number of leaves infected and severity was measured by total lesion area and average lesion area per leaf. LA demonstrated significant differences among lineages in two out of three wounded detached leaf experiments; however, SC, IP_w and AULEC showed no consistent significant differences among lineages. There was also no consistent significant cultivar by lineage interaction among the wound inoculated experiments. The non-wounded whole plant dip inoculations showed a trend towards a difference between the NA1 lineage and EU1 and NA2 (0.1>p>0.05) but variability among isolates within lineages means that these slight differences are not statistically significant. In one out of the two experiments on whole plants significant differences between isolates within lineages were observed (p<0.026). style="">

This study indicates that there are minor differences in fitness components among P. ramorum clonal lineages but suggests also that within lineage variability is great. Experiments are ongoing with an increased sample size of 10 isolates per clonal lineage.