Sensitivity of two Podosphaera aphanis populations to disease control agents

Powdery mildew (Podosphaera aphanis) causes severe losses in strawberry crops. The two aims of this study were to evaluate the efficacy of powdery mildew control agents and compare two geographically distinct populations of the pathogen (from northern Italy and Israel). Germination and germ tube elongation of P aphanis conidia were tested in the presence of several control agents using both leaf and glass slide bioassay's. The leaf bioassay was found to be more suitable for comparing the efficacy of control agents. Agents found effective were used to compare the relative sensitivities of samples from the Italian and Israeli populations. Various chemical agents, including those containing sulphur, strobilurin and triazole fungicides, were more effective than salts and biocontrol agents on both populations. The Italian and Israeli R aphanis populations were found to be similar in sensitivity to all the agents. Similarly, DNA analyses showed that the Israeli and Italian samples were nearly identical (100-99% similar) based on, sequence analyses of a 359 bp fragment of the ITS 1-2, region and 6 random fragments totalling 2800 bp. ITS sequence analysis of an isolate of the synonymous species Sphaerotheca aphanis from strawberry was 100% identical to R aphanis, compared to 97, 85 and 67% for S. pannosa, S. fuliginea and Leveillula taurica, respectively. RI Pertot, Ilaria/B-9521-2011