Phytophthora palmivora is restricting tropical plant pathogen for tropical and subtropical crops. Management of the pathogen has relied mostly on cultural practices and plant breeding; however, absence of these strategies in crops such as oil palm have resulted in catastrophic epidemics. During the present study a total of 150 isolates of P. palmivora obtained from 17 countries and 16 different hosts were studied. Differences in morphology, cultural growth, virulence and in-vitro and in-vivo response to nine fungicides, including the broadly used active ingredient mefenoxam, were elucidated. Differences in sporangia, chlamydospore and oospore measured parameters were observed among isolates; however, they ranged within those described for the species. Differences in sporangia length, sporangia breadth, and chlamydospore diameter seems to be influenced by the host family. This influence was not observed for the oospore characteristics. Virulence of isolates from Citrus spp. were also distinguishable from the rest of families when they were tested on apples; the lesion diameter of this isolates (31.9 mm) was about 10 millimeters shorter than the average of the rest of the families (41.7 mm). No significant differences were observed within the other families. Isolates from the Americas caused larger lesions than those from Asia and Oceania. Only one isolate of P. palmivora (13720) was intermediately sensitive to mefenoxam at 100 ppm.In order to identify possible active ingredients that could be used to manage diseases caused by P. palmivora, efficacy of the fungicides captan, cyazofamid, dimethomorph, fluopicolide, mandipropamid, mefenoxam, oxathiapiprolin, zoxamide, and potassium phosphite were tested on petunia bedding plants. Total control of the disease was observed at 21 days after inoculation with mefenoxam, captan and oxathiapiprolin. Success in disease control was followed by manidporpamid (83%), and fluopicolide and dimethomorph and zoxamide which presented an intermediate level of control (50%). The rest of the fungicides were not different from the inoculated control.With the exception of potassium phosphite, the in-vitro response to the selected fungicides was evaluated using the spiral plating technique. The effective concentration (EC50) for each isolate was elucidated by measuring the distance (mm) between the center of the plate and the point where 50% of lateral growth was observed. The data generated during the study were analyzed using the R-package ECX, developed during the present study. All products were effective in controlling most of the isolates at the selected ranges. Four isolates were not controlled with mefenoxam; however, the maximum dose of mefenoxam evaluated (0.289 mg/L) with the spiral plating technique does not implies resistance. The present study demonstrates the variability of the P. palmivora population, and provides some insight in its control using fungicides.
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