The reaction of ten rubber clones (Hevea benthamiana) to three isolates of Microcyclus ulei (P. Henn.) v. Arx from two pathogenicity groups I and II was evaluated. The monocyclic parameters incubation period, latent period, lesion size and reaction type were studied. A conidial suspension of 2 χ 105 conidia/ml was inoculated on the abaxial leaflet surface in the B1/B2 stage; the seedlings were placed a humid chamber during 24 hours at 24 ± lºC, then transfered to a growth chamber at the same temperature until the last evaluation at 15 days. The majority of the clones showed resistance to the three isolates. There was no significant interaction between clones and isolates in relation to incubation period, but there was significant interaction between clones and isolates in relation to lesion diameter. The clones CNSAM 8218 and CNSAM 8219 were highly resistant and showed the smallest mean lesion diameter when inoculated with isolate EB1, while CNSAM 8219 showed a small mean lesion diameter when inoculated with isolate EB2 also. At the other extreme, the clone CNSAM 8205 showed the largest mean lesion diameter when inoculated with isolate EB1 and the same reaction as clone CNSAM 8204 when inoculated with isolates EB2 and MB1 and clone CNSAM 8201 when inoculated with isolate EB2. These clones show vertical resistance making their unsuitable for the rubber breeding program that plans to obtain clones with horizontal resistance to M. ulei.
leaf blight; vertical resistance