Reaction of cucumber hybrids to Corynespora cassiicola in Amazonas

The target spot caused by the fungus Corynespora cassiicolais the major disease affecting tomato shoot in the north region of Brazil. In Amazonas State, this pathogen has caused severe damage to the production of cucumber plants, both in greenhouses and in the field. The aim of this study was to evaluate the reaction of ten cucumber genotypes to C. cassiicola.The experiment was conducted in a greenhouse, and a completely randomized design with ten treatments and ten replicates was adopted. The following cucumber cultivar and hybrids were evaluated: cultivar Aodai, and hybrids Japanese General Lee F1, Hokushim, Japanese Hybrid F1 (Soudai), "Jóia", Marketmore 76 (long green), Natsubayashi, Natsu Suzumi, Sprint 440 II and Tsuyataro. The pathogen isolates were obtained from leaves of naturally infected cucumber plants and multiplied on PDA culture medium. The plants had their first two definitive leaves inoculated with inoculum suspension at the concentration of 104 conidia mL-1 and kept in a humid chamber during 48 hours. Severity was assessed and the area under the disease progress curve (AUDPC) was calculated for each treatment. There was variation in the reaction of genotypes to the pathogen, and cultivar Aodai showed the smallest AUDPC, considered resistant. The hybrids Hokuchim, Soudai, Long Green and Natsubayashi presented the lowest AUDPC values in contrast to Tsuyataro, the most susceptible hybrid.