OCCURRENCE OF COMMON SCAB IN POTATO-TUBERS ALTER FOLIAR TREATMENT WITH GLYCINEBETAINE UNDER GLASSHOUSE CONDITIONS

A single foliar spray with 2.5 mM glycinebetaine (GB) was applied on p otato (Solanum tuberosum L.) cvs. Matilda, Sabina and Saturna grown in a sand bed infested with Streptomyces scabies (Thaxter) Waksman & Hen rici at tuber initiation. A period of drought was maintained after GB treatment to enhance scab infection. Legit models were used to compare scab incidence in all harvested tubers (n = 622) and the type of scab in the symptomatic tubers (n = 382), whereas the tuber surface areas covered with scab lesions were compared using ANOVA. A 10 g increase i n tuber weight increased the odds of scab incidence by 11.3%. Scab inc idence was lowest in Sabina and highest in Matilda. Raised scab and su perficial scab were common in all cultivars, but pitted scab developed only in a few tubers of Sabina and Matilda. Among the scabby tubers, the incidence of raised scab was highest in Sabina and lowest in Satur na. The mean surface area covered with scab was 32.8% in Matilda, 11.7 % in Saturna and 7.5% in Sabina. Treatment with GB slightly reduced th e severity of scab symptoms, as shown by the reduction in the proporti on of tubers with raised scab among the scabby tubers (odds 0.60). No effect on the incidence of scab or the tuber area covered with scab le sions was detected following GB treatment.