Comparing Inoculation Methods for in Vitro Evaluation of Resistance to Blackleg Disease in Potato Cultivars

To find the best inoculation method for evaluation of the resistance in potato genotypes against bacterial blackleg caused by Pectobacterium atrosepticum under in vitro conditions, five inoculation methods were compared. In vitro grown explants of five potato genotypes were inoculated with different inoculation methods, then placed on MS solid medium and incubated at 23?C with 70% relative humidity under the light regime of 16 hours a day. After the appearance of symptoms, the efficiency of inoculation methods was then recorded based on the severity of disease symptoms in potato genotypes: Farmosa, Agria, Picaso, Marfona and a wild potato genotype ?Solanum phureja'. Plantlets inoculated by piercing the crown with sterile toothpick inoculated in bacterial suspension of 108 cfu/ml showed the most severe symptoms. Based on all experiments, cultivar Marfona showed higher resistance among all cultivars and, cultivar Agria was the most susceptible. Finally, after witnessing the reactions of different varieties to inoculation methods and comparing them with previous evaluations of resistance in greenhouse conditions, the crown treatment employing sterile toothpick after infection in 108 cfu/ml bacterial suspension was selected and introduced as the best evaluation method of in vitro potato explants against blackleg.