SCREENING OF POTATO GENOTYPES AT SEEDLING STAGE AS FOR THE RESISTANCETO BACTERIAL WILT

Five populations obtained by open pollination of the clones 385312-2=P op.I, 388285-14=Pop.II, 385317-1=Pop.III, 388083-9=Pop.IV, and 388307- 4=Pop.V, and cv. Mantiqueira (susceptible control), were used to scree n potato seedlings as for resistance to Pseudomonas solanacearum True seeds, treated with gibberelic acid (2000 ppm/24 h), were sown in ster ile soil. After incubation (16 h on fluorescent light/20+/-1 degrees C /10 days), the seedlings were transplanted to trays with individualize d cells in greenhouse. The inoculation was done by immersing the trays , without irrigation on the day of inoculation, in a bacterial suspens ion (10(8) UFC/ml-10 minutes) of P. solanacearum ten days after transp lanting. The evaluation was done by counting wilted plants during two months. Eleven plants survived from 505 inoculated seedlings in the gr eenhouse. The tubers obtained from selected plants were used in a fiel d trial. In the field trial, nine clones were resistant or moderately resistant, indicating that 72.7% of the selected clones in greenhouse had some resistance level in the field. Clones I-1, I-2 (Pop.I) and II -1 (Pop.II) showed the best levels of resistance to bacterial wilt. Al though subjected to escapes, the method has shown effectiveness on the selection of genotypes resistant to bacterial wilt in an early stage of a breeding program.