Evaluation of the Existence of a New Race of Bremia lactucae on Lettuce

Lettuce is one of the most consumed leafy vegetables in Turkey. The production of lettuce has been to get difficult due to infestation of cultivation areas with Bremia lactucae . This pathogen is genetically very variable. Pathogenic variation of B. lactucae has not been studied yet in Turkey. The objective of this study was to monitore the races of B. lactucae in the two geographic regions of Turkey. During the lettuce growing season in May and October 2018, totally 72 diseased leaf samples containing B. lactucae sporangia were collected from the fields of Bartın and Ankara provinces. From these samples 6 isolates were obtained. After a multiplication procedure, in which the susceptible lettuce cultivar 'Green Towers' was used, the B. lactucae sporangia were inoculated in differentiating lettuce cultivars. The response of the lettuce seedlings to pathogen was evaluated on the 7, 11 and 14 days after inoculation. The qualitative method was used for the assessment of infected seedlings. Sextet codes of Ankara and Bartın isolates were found as 44-00-01 and 13-03-04 respectively. The sextet codes of Turkish isolates did not match any of the present 37 races of B. lactucae . This result suggests that our isolates may be new races or pathotypes.