Vol. 5 (1996): 601-608. Research Note Occurrence of common scab in potato tubers after foliar treatment with glycinebetaine under glasshouse conditions Elina Tuomola Department of Plant Production, PO. Box 27, FIN-00014 University ofHelsinki, Finland Hannu Rita Department ofForest Resource Management/Statistics, PO. Box 24. FIN-00014 University ofHelsinki, Finland Paavo Kuisma Potato Research Institute, Ruosuontie 156, FIN-16900 Lammi, Finland Susanne Somersalo, Eija Pehu Department of Plant Production, PO. Box 27, FIN-00014 University ofHelsinki, Finland Kari Jokinen Cultor Ltd., Finnsugar Bioproducts, PO. Box 105, FIN-00241 Helsinki. Finland Jari P.T. Valkonen Department of Plant Production, PO. Box 27, FIN-00014 University ofHelsinki, Finland. Present address: Institute ofBiotechnology, PO. Box 56, FIN-00014 University of Helsinki, Finland, e-mail: jari.valkonen@helsinki.fi 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 (Thax- ter) 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 symp- toms, 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. Key words: disease control, logit model, potato, Solanum tuberosum, Streplomyces scabies © Agricultural and Food Science in Finland Manuscript received September 1996 601 AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=IOnGtzeNIO0ueZPV.Ltz8h1Fp8-ASCqLOdODCOw.FBA5fDdr8WTbkEPej7_fAOSyuXScaciYxdqgqU-PtgOoJszdGCgOA9zE0uOtx9N5yG3Gr_kJo9_71Z3bl5Srsg_y51GQ_4DcjtZa_PlSRHZNPp53oRs6vsTuWPxJF8ZAPjV-5oW3pweKpnw7qqNfQArcR-HAUsGX018wACIjsip8PxjB4HgEyUJ0Lyg4DOrgV5abE8TpOvxsyzNux1ileUdBph5xG4OBCTsXKP0cmaQfI9Znm56uFOPo2qgN60i7rfZAdR39THPw63CE8WoL5DbtHK-YdC2qFj-4YY8FsVfmsUFLWw3_--AB0DqO73bK3797F5iHB2eCD042SV1PHGCOu1s3bPOAtf8C6xKgGwwQzyQPC38Pz-VAZXxYXg Tuomola, E. et al. Effect ofglycinebetaine on common scab in potato Introduction The scab disease of potato (Solanum tuberosum L.) is caused by the actinomycete species of the genusStreptomyces. S. scabies (Thaxter) Waks- man & Henrici causes common scab in most ar- eas where potatoes are grown, but there are also other species ofStreptomyces which cause symp- toms similar to common scab or symptoms de- scribed as russet or netted scab (Hooker 1981, Scholte and Labruyere 1985,Keinath and Loria 1989, Doering-Saad et al. 1992, Faucher et al. 1992). Common scab occurs as three types of symptoms which impair the quality of tubers: superficial scab, raised scab (cushionlike or erumpent) and pitted scab (extension into the tuber) (reviewed by Locci 1994). Here, unless otherwise stated, the term scab refers to com- mon scab caused by S. scabies. The type of scab and the proportion of the tuber surface covered with scab correlate with and are determinedby the level of susceptibility of the potato cultivar (Leach et al. 1938, Bjor and Roer 1980, Goth et al. 1991). In contrast, the incidence of scab in tubers is determined by environmental factors such as soil pH and mois- ture. Scab incidence can be lowered by bringing pH below 5.2, but this practice also reduces the availability of nutrients to potato plants (Martin 1923,Loria 1991). Maintenance of soil moisture close to field capacity by irrigation during the first 4-5 weeks of tuber formation can greatly reduce scab incidence (Martin 1923, Lapwood et al. 1973). However, irrigation can increase the incidence and severity of other soil-borne dis- eases (Loria 1991) and does not always reduce scab (Goto 1985, Doering-Saad et al. 1992). Potato cultivars vary in their resistance to scab, but no cultivar is fully resistant (Bjor and Roer 1980, Loria 1991). Attempts have there- fore been made to reduce scab in potato by af- fecting the physiology of potato plants through chemical treatments. Foliar spray with the growth retardants daminozine and 3,5-dichlo- rophenoxyacetic acid (3,5-D) reduces scab in tubers. Both compounds improve tuber resist- ance to scabrather than have bactericidal effects on the pathogen (Mclntosh 1979, Mclntosh et al. 1981, Burrell 1984, Mclntosh et al. 1988). Glycinebetaine (GB) is a compatible solute which accumulates naturally in the cells of some plant species under osmotic stress, but is not syn- thesized in many important crop species, e.g., potato (Gorham 1995). GB stabilizes cell mem- branes (Jolivet et al. 1982) and certain photo- synthetic structures (Papageorgiou et al. 1991). The physiological role of GB has not been fully established but it may act as an osmoregulatory compound (Robinson and Jones 1986). As high- er scab incidences coincide with dry soil and drought stress of potato plants in the field (Mar- tin 1923, Loria 1991), it is suggested that the reduction in drought stress achieved with GB treatment might also reduce scab incidence. This hypothesis is supported by unpublished findings of R Kuisma and K. Jokinen from potato field plots sprayed with GB. In this study, we tested the effects of GB treatment on potato common scab under controlled glasshouse conditions. Material and methods Experimental design Potato cvs. Matilda, Sabina and Saturna were chosen for the experiments because they are commonly grown in Finland and, as shown by observations in the field, seem to differ in sus- ceptibility to scab, Matilda being the most high- ly susceptible. On the other hand, Saturna is the most sensitive to drought, which may result in a significantly reduced mean tuber size under dry growth conditions (L. Pietilä and P. Kuisma, unpublished). Pathogen-tested minitubers were obtained from the Seed Potato Center, Tyrnävä, Finland. 5. scabies strains SSCIIO and SSCI22 iso- lated from potato cvs. Record and Bintje, respec- tively, infected in the field in Jokioinen, Finland, and known to cause severe scab symptoms on 602 AGRICULTURAL AND FOOD SCIENCE IN FINLAND potato (Oravuo 1994), were kindly provided by 1. Kankila, Plant Breeding Section, Institute of Plant and Soil Science, Agricultural Research Centre, Finland. They were grown on potato dex- trose agar (Difco) for 3 weeks at 24°C, each sus- pended in 10 I of sterile distilled water (5.4 x 106 colony- forming units per ml) and mixed into a bed of fine sand (6.0 x 1.1 m, depth of sand 35 cm) in the glasshouse. The sand was fertilized using an N:P;K fertilizer (8:10:12) at 75 kg N/ha. Tubers were sprouted at room temperature (mean sprout length 5 mm) and planted in a sand bed on January 9. The plants were arranged in three blocks in the bed, each block including ten plants ofeach cultivar in two rows (five plants per row). The moisture in the sand bed was monitored at seven measurement points using the Bouyoucos Moisture Meter (Industrial Instruments, Michi- gan State Board of Agriculture, Cedar Grove, Essex, N.J., USA) and was adjusted by irriga- tion to simulate the fluctuation of soil moisture in the field plots at the Potato Research Station during the 1994 growth season (Fig. 1). The plants were grown under natural daylight extend- ed to 18 h by illumination with sodium halide lamps (150-1100 (imols“'irr 2). Daily mean tem- peratures were 20°C (17-25°C). The time for GB treatment was selected to correspond to the growth stage of the potato plants and the soil moisture in order to mimic the application time in the field in 1994. Within each block, one row (five plants) of each culti- var was treated with a single foliar spray of 2.5 mM GB (pH 8.0) (Cultor Ltd. Finnsugar Bio- products, Finland) diluted with distilled water 6 weeks after planting. At this time, flower buds had formed in all cultivars but they had not yet opened. The amount of GB used for the treat- ment corresponded to 1.17 kg/ha. Control plants were sprayed with distilled water. Data analysis The tubers were lifted on May 3 (124 days after planting). The tuber surface area covered by scab was determined with the method described by Schöber (1984). Each tuber was also evaluated for the type of scab: no scab, superficial scab, raised scab or pitted scab (Hooker 1981). This classification was appropriate, as each tuber showed only one type of scab. ANOVA containing five factors (cultivar, GB treatment, tuber weight class, scab type and block) was used to detect differences in the mean surface area covered by scab; only tubers show- ing scab symptoms were analysed (SAS Insti- tute Inc., General Linear Models Procedure). Scab incidence and type were analysed in two stages. First, the response was reduced to a bi- Fig. I. Available water(A) at 15 cm depth in the sand bed in the glasshouse during this study, and (B) at 15 and 25 cm depths in soil of the potato test plots in the field at the Potato Research Institute, Lammi, in 1994, from emergence to maturity of potato plants. T, time of a single spray with glycinebetaine. 603 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Tuomola, E. et al. Effect ofglycinebetaine on common scab in potato nary variable indicating only the incidence of scab, irrespective of its type. Second, to analyse the type of scab, only scabby tubers were includ- ed. Only a few tubers showed pitted scab (Ta- ble 1), and so were excluded from analysis. Thus, the type of scab also became a binary variable (superficial or raised scab). Logit models are suitable for analysing data with a binary response (Collett 1991)and can be powerful tools in many kind ofstudies on plants (Mäkäräinen et al. 1994, Linden et al. 1996, Malkamäki et al. 1996). Thus, both response variables, i.e., the incidence and the type of scab, were analysed using logit mod- els (SAS Institute Inc., GenMod Procedure). The test potato cultivars were of similar ma- turity types. Tuber weight (size) and age do not strictly correlate, but it is expected that the weight classes of the largest and smallest tubers contain the most mature and juvenile tubers, re- spectively (Burton 1989). The length of time available for the development of scab symptoms is proportional to tuber age, because infection occurs when tubers are young (Adams and Lap- wood 1978, Hooker 1981). It was thereforecon- sidered important to test whether tuber age, as indirectly and roughly indicated by weight, had any effect on scab. Because the mean tuber weight differed among the test cultivars (Fig. 2), tubers of each cultivar were divided into four weight classes with an equal number of tubers in each class. Results Surface area covered by scab A total of 382 tubers of the 622 tubers harvested from the three cultivars had some form of scab (Table 1). Analysis of the surface area covered with scab using ANOVA showed that cultivars differed (p = 0.0001): the mean surface area cov- ered with scab was greatest in Matilda (32.8% coverage), intermediate in Saturna (11.7%) and lowest in Sabina (7.5%) (p = 0.001). Tubers in the higher weight classes and with raised scab had a larger surface area covered by scab lesions (p = 0.0001 and p = 0.002, respectively) than did those withsuperficial scab. The tuber weight class x scab type x block interaction was signif- icant (p = 0.002) whereas the other interactions were non-significant. No effect due to GB treat- ment could be detected. Incidence of scab Tuber weight was significantly associated with scab incidence (Table 2), but had no interaction with GB treatment or cultivar (p = 0.24 and p = 0.48, respectively). An increase of the tuber weight by 10 g increased the odds of scab inci- dence by 11.3%. Scab incidence was lowest in Sabina, intermediate in Saturna and highest in Matilda (Table 2). Treatment with GB had no effect on scab incidence (p = 0.41) and no inter- action with cultivars (p > 0.13). Type of scab Raised scab and superficial scab were the most common types of scab observed (Table 1). Fig. 2. Distribution of 622 harvested tubers by weight, I, < 10 g; 2, 10-29 g; 3, 30-50 g; 4, > 50 g. 604 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Table I. The numbers (and percentages) of tubers with different types of scab after treatment of plants with a single foliar spray with glycinebetaine. Controls were sprayed with distilled water, (n =622) cv. Matilda cv. Sabina cv. Satuma treated control treated control treated control a) No scab 31 (24.6%) 30 (23.3%) 52 (50.5%) 52 (53.6%) 31 (44.9%) 44 (44.9%) b) Pitted scab 3 (2.4%) 5 (3.9%) 1 (1.0%) 6 (6.2%) 0 0 c) Superficial or raised scab 92 (73.0%) 94 (72.8%) 50 (48.5%) 39 (40.2%) 38 (55.1%) 54 (55.1%) - superficial scab 65 (70.7%) 58 (61.7%) 14 (28.0%) 7 (17.9%) 38 (100%) 52 (96.3%) -raised scab 27 (29.3%) 36 (38.3%) 36 (72.0%) 32 (82.1%) 0 2(3.7%) Total (a +b + c): 126 (100%) 129 (100%) 103 (100%) 97 (100%) 69 (100%) 98 (100%) Table 2. Logit analysis of scab incidence (including the differences between blocks). P-value Comparison Coefficient (Wald test) O.R. a C.I.b Treated vs. control -0.01 0.95 0.99 0.71-1.39 Cultivar Sabina vs. Matilda -1.29 0.00 0.28 0.18-0.41 Satuma vs. Matilda -1.00 0.00 0.37 0.24-0.56 Weight 1 0.11 0.00 1.11 1.09-1.14 a 0.R., odds ratio. O.R. = 1 is equivalent to no difference in the comparison. O.R. different from 1 is interpreted as follows: for example, O.R. = 0.99 (lower than 1) indicates that the incidence of scab in the treated plants is lower than in the control plants. b C.1., 95% confidence interval. If unity = 1 is within the C.1., this indicates that the comparison does not show a significant difference (p = 0.05). c per 10 g increase in tuber weight. Table 3. Logit analysis of scab type (including the differences between blocks). P-value Comparison Coefficient (Wald test) O.R. a C.I. b Treated vs. control -0.51 0.06 0.60 0.36- 1.01 Cultivar Sabina vs. Matilda 1.89 0.00 6.60 3.67-11.87 Satuma vs. Matilda -3.19 0.00 0.04 0.01- 0.17 a 0.R., odds ratio. O.R. = 1 is equivalent to no difference in the comparison. For the interpretation ofO.R. differing from 1, see Table 2. b C.1., 95% confidence interval. If unity = 1 is within the C.1., this indicates that the comparison does not show a significant difference (p = 0.05). Among the scabby tubers, the incidence of raised scab was highest in Sabina, intermediate in Ma- tilda, and lowest in Saturna (Table 3). Pitted scab developed in only a few tubers of Sabina and Matilda and, as mentioned above, was not in- cluded in statistical analysis. Weight and the GB 605 Vol. 5 (1996): 601-608. AGRICULTURAL AND FOOD SCIENCE IN FINLAND Tuomola, E. et al. Effect ofglycinebetaine on common scab in potato treatment by cultivar interaction were not sig- nificant (p > 0.37). Some reduction in raised scab, which was close to the statistically signif- icant level (p = 0.0566), was observed among the scabby tubers in all cultivars combined (odds 0.60) following GB treatment (Table 3). Discussion 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, although pitted scab was also observed in a few tubers. The incidence of scab was also low in Saturna but symptoms were mild (super- ficial scab). Matilda showed the highest inci- dence of scab, the largest surface area covered by scab and all three types of scab. Many previ- ous studies have suggested that the type of scab and the tuber surface area covered with scab le- sions indicate the relative level of resistance to scab in potato cultivars, whereas the incidence of scab in tubers is dependent on environmental factors such as soil pH and moisture (Martin 1923, Leach et al. 1938, Bjor and Roer 1980, Goth et al. 1991, Loria 1991). Thus, the inci- dence of scab seems to be associated with the initial infection process, whereas the type ofscab and the surface area covered with scab are asso- ciated with physiological processes in the tuber which take place after infection and result in the formation of scab lesions. Neither the process of infection of potato tubers by S. scabies nor the development of scab symptoms is well-de- scribed at the molecular and physiological lev- el. The production of cell wall-degrading en- zymes by S. scabies is, however, known to play a role in penetration and that of the vivotoxin thaxtomin in symptom development (Adams and Lapwood 1978, Hooker 1981, Lawrence et al. 1990, Locci 1994). The environmental condi- tions in our study were the same for all three cultivars. Differences between cultivars were, however, observed in all three of the above var- iables implying that each can be affected by the cultivar. It is therefore suggested that Sabina re- sists infection but not symptom development, Saturna resists both infection and symptom de- velopment, but that Matilda has little resistance to either. Severe occurrence of common scab in pota- toes in the field is known to be associated with drought and can usually be controlled by irriga- tion, but the reasons for these phenomena are not understood (Martin 1923,Adams and Lap- wood 1978, Loria 1991). For example, it is not known whether the conditions in dry soil are more beneficial to S. scabies, which is aerobic, and, thus, exacerbate the virulence of the patho- gen, or whether the drought stress of potato plants increases their susceptibility to the scab disease, or whether both mechanisms are in- volved. Here, we tested the latter hypothesis by treating potato plants with GB, a solute thought to mitigate drought stress (Robinson and Jones 1986, Agboma et al. 1996). Our results suggest- ed that the severity of scab symptoms was re- ducedby GB treatment, as a slightly smallerpro- portion of tubers showed raised scab. The pro- portion of tubers with pitted scab also seemed to be lower after GB treatment (Table 1), but this was not tested statistically. It should be noted that not all observations were independent, as several tubers from a single plant were included in the analysis and, thus, the statistical signifi- cance of results should be treated with some cau- tion. Because GB treatment had no significant effect on the incidence of infection (i.e., the in- cidence of scabby tubers), it is suggested that GB affected the physiology of potato tubers and subsequently the development of symptoms, rather than the initial infection by S. scabies. Raised scab was more common in tubers with a larger surface area covered with scab lesions (p = 0.002). However, the extentof the tuber sur- face area covered with scab lesions was not re- duced by GB treatment. Although the treatment seemed to reduce symptom severity it may not have been strong enough to reduce lesion area. 606 AGRICULTURAL AND FOOD SCIENCE IN FINLAND The molecularaction of GB in potato cells is not fully understood. It is known that GB is trans- located in potato plants (P. Mäkelä, E. Tuomola, J. Valkonen and S. Somersalo, unpublished). It is hypothesized then that GB is translocated from foliage to tubers, thus affecting scab develop- ment via changes in plant physiology rather than via direct antimicrobial activity, as shown pre- viously for some other compounds (Mclntosh 1979, Mclntosh etal. 1981, Burrell 1984, Mcln- tosh et al. 1988). Foliarly applied GB has increased yields of tomato (Lycopersicon esculentum Mill., Sola- naceae), the highest yield increases having been achieved at an application rate of 1-2 kg/ ha (Mäkelä et al., unpublished), and also of many grain crops, under drought (Agboma et al. 1996). The application rate of GB used for potato in our study was at the lower limit of an effective application rate for tomato, a factor that may par- tially explain the lack of effect on tuber yield. The use of higher amounts of GB might also control scab more efficiently. Acknowledgements: Financial support from Cultor Ltd. Finnsugar Bioproducts and the Academy ofFinland is grate- fully acknowledged. References Adams, M.J. & Lapwood, D.H. 1978. Studies on the len- ticel development, surface microflora and infection by common scab (Streptomyces scabies) of potato tubers growing in wet and dry soils. Annals of Applied Biology 90: 335-343. Agboma, P.C., Jones, M.G.K., Peltonen-Sainio, P., Rita, H. & Pehu, E. 1996. Exogenous glycinebetaine en- hances grain yield of maize, sorghum and wheat grown under two supplementary watering regimes. Journal of Agronomy and Crop Science, in press. Bjor.T. & Roer, L. 1980. Testing the resistance of potato varieties to common scab. Potato Research 23: 33-47. Burrell, M.M. 1984. Inhibition of browning, phenoxyace- tic acids and phenolic metabolism in potato tuber discs: a model system to study chemicals that control common scab. Plant Pathology 33: 325-336, Burton, W.G. 1989. The potato. 3rd ed. Longman Scien- tific & Technical, New York, USA. 742 p. Collett, D. 1 991. Modelling binary data. Chapman & Hall, London, UK. 369 p. Doering-Saad, C., Kämpfer, P., Manulis, S., Kritzman, G., Schneider, J., Zakrzewska - Czerwinska, J., Schrempf, H. & Barash, 1. 1992.Diversity among Strep- tomyces strains causing potato scab. Applied and Envi- ronmental Microbiology 58: 3932-3940. Faucher, E., Savard, T. & Beaulieu, C. 1992. Charac- terization of actinomycetes isolated from common scab lesions on potato tubers. Canadian Journal of Plant Pa- thology 14:197-202. Gorham, J. 1995. Betaine in higher plants: biosynthesis and role in stress metabolism. In: Wallsgrove, R.M, (ed.), Aminoacids and their derivatives in higher plants. Uni- versity Press, Cambridge, UK. p. 172-203. Goth, R.W., Haynes, K.G. & Wilson, D.R. 1991. Evalu- ation and characterization of advanced potato breeding clones for resistance to scab by cluster analysis. Plant Disease 77:911-914. Goto, K. 1985. The relative importance of precipitation and sugar content in potato peel for the detection of the incidence of common scab (Streptomyces scabies). Soil Science and Plant Nutrition 31: 419-425. Hooker,W.J. 1981 . Compendium of potato diseases.The American Phytopathological Society, St, Paul, MN, USA. p. 33-34. Jolivet, Y., Larher, F. & Hamelin, J. 1982. Osmoregula- tion in halophytic higher plants: the protective effect of glycine betaine against the heat destabilization of mem- branes. Plant Science Letters 25:193-201. Keinath, A.P. & Loria, R. 1989. Population dynamics of Streptomyces scabies and other actinomycetes as relat- ed to common scab of potato. Phytopathology 79: 681- 687. Lapwood, D.H., Wellings, L.W. & Hawkins, J.H. 1973. Irrigation as a practical means to control potato common scab ( Streptomyces scabies): final experiment and con- clusions. Plant Pathology 22: 35-41. Lawrence, C.H., Clark, M.C. & King, R.R. 1990. Induc- tion of common scab symptoms in aseptically cultured potato tubers by the vivotoxin, thaxtomin. Phytopatholo- gy 80: 606-608. Leach, J.G., Krantz, F.A., Decker, P. & Mattson, H. 1938. The measurement and inheritance of scab resist- ance in selfed and hybrid progenies of potatoes. Journal of Agricultural Research 56: 843-853. Linden, L., Rita, H. & Suojala, T. 1996. Logit models for estimating lethal temperatures in apple. HortScience 31: 91-93. Locci, R. 1994. Actinomycetes as plant pathogens. Eu- ropean Journal of Plant Pathology 100: 179-200. Loria, R. 1991. Potato scab. In: Diseases of potato. New 607 Vol. 5 (1996): 601-608. AGRICULTURAL AND FOOD SCIENCE IN FINLAND Tuomola, E. et al. Effect ofglycinebetaine on common scab in potato York State Integrated Pest Management Program Fact Sheet. Cornell Cooperative Extension, Ithaca, NY, USA. p. 725.80 Mäkäräinen, E., Rita, H.,Teperi, E. & Valkonen, J.P.T. 1994. Resistance to Spongospora subterranea in tuber- bearing and non tuber-bearing Sotanum spp. Potato Re- search 37: 123-127. Malkamäki, U., Clark, M.S., Rita, H., Valkonen, J.P.T. & Pehu, E. 1996. Analyses of solanaceous species us- ing repetitive genomic DNA sequences isolated from Sotanum brevidens. Plant Science 117: 121-129. Martin, W.H. 1923. Influence of soil moisture and acidity on the development of potato scab. Soil Science 16: 69- 73. Mclntosh, A.H. 1979. Decreased common scab inci- dence after foliar sprays of daminozide. Potato Research 22: 361-363. -, Bateman, G.L. & Chamberlain, K. 1988. Substituted benzoic and picolinic acids as foliar sprays against pota- to common scab. Annals of Applied Biology 112: 397- 401. - , Bateman, G.L., Chamberlain, K., Dawson, G.W. & Burrell, M.M. 1981. Decreased severity of potato com- mon scab after foliar sprays of 3,5-dichlorophenoxyace- tic acid, a possible antipathogenic agent. Annals of Ap- plied Biology 99: 275-281. Oravuo, M. 1994. Applicability of a “pot method” tor test- ing susceptibility to common scab (Streptomyces sca- bies) and for selection of breeding materials. M.S, The- sis, Department of Plant Production, University of Hel- sinki, Finland. 75 p. (In Finnish). Papageorgiou, Gr.C.M., Fujimura,Y. & Murata, N. 1991. Protection of the oxygen-evolving photosystem II com- plex by glycinebetaine. Biochimica et Biophysica Acta 1057: 361-366. Robinson, S.P. & Jones, G.P. 1986. Accumulation of glycinebetaine in chloroplasts provides osmotic adjust- ment during salt stress, Australian Journal of Plant Phys- iology 13: 659-668. Scholte, K. & Labruyere, R.E. 1985. Netted scab: a new name for an old disease in Europe. Potato Research 28: 443-448. Schöber, B. 1984. Methoden zur Prufung der Anfällig- keit von Kartoffelknollen fur den Gewöhnlichen Schorf. In: Potato Disease Assessment Keys. European Associ- ation for Potato Research, Wageningen,The Netherlands. SELOSTUS Glysiinibetaiinilla suoritetun lehvästöruiskutuksen vaikutus perunan rupisuuteen Elina Tuomola, Hannu Rita, Paavo Kuisma, Susanne Somersalo, Eija Pehu, Kari Jokinen ja Jari Valkonen Helsingin yliopisto, Perunantutkimuslaitos ja Cultor Finnsugar Bioproducts, Finland Perunaruven torjunta viljelyteknisin menetelmin on ongelmallista. Perunan fysiologiaan vaikuttavien ja ruven syntyä estävien kemiallisten aineiden kehittäminen tehostaisi ruven torjuntaa. Tässä tutki- muksessa perunarupea aiheuttavalla sädebakteerilla (Streptomyces scabies) saastutettuun hiekkapetiin is- tutettujen perunoiden (Matilda, Sabina ja Saturna) lehvästö ruiskutettiin glysiinibetaiinilla mukulanmuo- dostuksen alkaessa. Kontrolli ruiskutettiin tislatulla vedellä. Käsittelyn jälkeen kasvualustan annettiin olla jonkin aikaa normaalia kuivempana rupi-infektion edistämiseksi. Rupisten mukuloiden ja eri rupityyp- pien osuuksia sekä ruven peittämän pinta-alan eroja verrattiin. Riippumatta käsittelystä ja lajikkeesta, mukulan koon kasvaessa ruven esiintymisen toden- näköisyys kasvoi. Rupisten mukuloiden osuus oli suurin Matildassa ja pienin Sabinassa. Myös ruven peittämä mukulan pinta-ala oli suurin Matildassa ja pienin Sabinassa. Laakarupi ja kohorupi olivat ylei- siä kaikissa lajikkeissa, mutta syvärupea oli vain muutamissa Sabinan ja Matildan mukuloissa. Koho- rupea oli eniten Sabinassa ja vähiten Saturnassa. Gly- siinibetaiinikäsittely vähensi lievästi rupioireiden an- karuutta kaikissa lajikkeissa, mikä ilmeni kohorupis- ten mukuloiden osuuden vähenemisenä, mutta rupis- ten mukuloiden osuuteen ja ruven peittämään muku- lan pinta-alaan sillä ei havaittu olevan vaikutusta. 608 AGRICULTURAL AND FOOD SCIENCE IN FINLAND