Abstract
A single foliar spray with 2.5 mM glycinebetaine (GB) was applied on potato (Solatium tuberosum L.) cvs. Matilda, Sabina and Saturna grown in a sand bed infested with Streplomyces scabies (Thaxter) Waksman & Henrici at tuber initiation. A period of drought was maintained after GB treatment to enhance scab infection. Logit 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 in tuber weight increased the odds of scab incidence by 11.3%. Scab incidence was lowest in Sabina and highest in Matilda. Raised scab and superficial 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 Saturna. 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 the severity of scab symptoms, as shown by the reduction in the proportion 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 lesions was detected following GB treatment.
Highlights
The scab disease of potato (Solanum tuberosum L.) is caused by the actinomycete species of the genus Streptomyces
The three potato cultivars studied here differed in their response to common scab
Sabina had the lowest incidence of scab, but symptoms were severe in those tubers which developed scab symptoms; the most common type was raised scab, pitted scab was observed in a few tubers
Summary
The scab disease of potato (Solanum tuberosum L.) is caused by the actinomycete species of the genus Streptomyces. Foliar spray with the growth retardants daminozine and 3,5-dichlorophenoxyacetic acid (3,5-D) reduces scab in tubers Both compounds improve tuber resistance to scab rather than have bactericidal effects on the pathogen (Mclntosh 1979, Mclntosh et al 1981, Burrell 1984, Mclntosh et al 1988). As higher scab incidences coincide with dry soil and drought stress of potato plants in the field (Martin 1923, Loria 1991), it is suggested that the reduction in drought stress achieved with GB treatment might reduce scab incidence. This hypothesis is supported by unpublished findings of R Kuisma and K. We tested the effects of GB treatment on potato common scab under controlled glasshouse conditions
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