Hiltunen, Lea

Valkonen, J.P.T.

Virtanen, Elina

Ylikantola (Alanen), M.

Potato Research

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EAPR Pathology Section Meeting Jerusalem, Israel, 17 – 21 November 2013  Lea Hiltunen, Minna Ylikantola, Elina Virtanen & Jari Valkonen    USE OF THAXTOMIN A AS A SELECTIVE AGENT FOR SCREENING POTATO GENOTYPES FOR RESISTANCE TO COMMON SCAB 2 • Occurs worldwide • Affects the quality of tubers • Caused by several species of the genus Streptomyces  • Multicellular, filamentous, Gram-positive Actinobacteria • Well known for production of secondary metabolites • Seed- and soil-borne • Able to live saprophytically • Can infect other tap root crops  Potato common scab Pathogenicity in the genus Streptomyces  Thaxtomin  • Phytotoxin  • The main pathogenicity determinant  • The mode of action: inhibition of cellulose biosynthesis in plant cells  Other factors involved, but  not essential to pathogenicity • Virulence related genes are present in some plant pathogenic Streptomyces species   3 4 Compound     R1 R2 R3 R4 R5 R6    1  Thaxtomin A   Me  OH Me  H OH H   2  Thaxtomin A o-isomer   Me  OH Me  OH H H    3  Thaxtomin C   Me  H H H H H   4  Thaxtomin B   Me  OH Me  H H H   5  C-14 deoxy thaxtomin B Me  H Me  H H H   6  Hydroxythaxtomin C  Me  OH H  H H H   7  Thaxtomin A p-isomer   Me  OH Me  H H OH   8  Hydroxythaxtomin A  Me  OH Me  H OH OH   9 15-de-N-methylthaxtomin A Me  OH H  H OH H 10 12-de-N-methylthaxtomin A H  OH Me  H OH H 11 des-N-methylthaxtomin C H  H H  H H H Thaxtomins No reliable control measures  5 Measure Reliability Clean seed Insufficient; Streptomyces is endemic, ubiquitous, soil-borne Low soil pH (< 5.2) Can fail, environmentally unfriendly Irrigation during early tuber formation Successful in some locations Crop rotation Ineffective Soil amendments Results variable, inconsistent Sulfur fertilisers Reduces scab severity in some locations Chemical control (soil fumigation) Environmentally unfriendly, expensive Seed treatment with chemicals  Insufficient Biological control Has potential, but results variable Resistant plant varieties Most reliable, cost-effective and environmentally friendly, but no known complete resistance • Would it be possible to use thaxtomins for screening potato genotypes in vitro for thaxtomin sensitivity?  • Does the thaxtomin sensitivity in vitro reflect scab sensitivity in the field?   6 Can we utilise thaxtomins in resistance breeding? 7  224 nm380 nmIVIIIIIIIIIIIIV-0.2 –1.2 AU Time (min)ICompound     R1 R2 R3 R4 R5 R6 I Thaxtomin A    Me OH Me H OH H II Thaxtomin A o-isomer  Me OH Me OH H H III Thaxtomin B   Me OH Me H H H IV C-14 deoxy thaxtomin B  Me H Me H H H • Thaxtomins were produced by  culturing strains of S. scabies and  S. turgidiscabies in oat meal broth  • Four thaxtomin compounds were  isolated and identified Hiltunen et al., J Agric Food Chem 2006 Production of thaxtomins in vitro Effects of thaxtomins on micropropagated potato 8 Inhibition of growth by thaxtomins 9 Hiltunen et al., J Agric Food Chem 2006 10 02040608010012014016018020091053849101201069085 2896511810026562948Relative shoot height (%)GenotypeMatilda Sabinahigh tolerance high sensitivity Responses of potato genotypes* to thaxtomin A in vitro (0.1 μg ml-1) ranged from total inhibition of growth to stimulated growth   Hiltunen et al., Plant Pathol 2011 * cv. Ciklamen x cv. Superb (SW01015) 11 0 5 10 15 20 25 30 35 40 45 100 90 38 9 Matilda 20 48 101 2 56 29 105 118 Sabina 49 Scab index Genotype The selected potato genotypes were tested for their sensitivity to common scab in the glasshouse Hiltunen et al., Plant Pathol 2011 Scab index = scab type x surface area covered by scab x 100/33 Correlation of the results from the in vitro bioassay and the glasshouse experiment  12 13 1015202530354045100Matilda65 2 9381012690858920118Sabina29564910648GenotypeScab index  a        a     ab    bc     bc    bc      bc    bc    bc    bcd   bcd   bcd  bcde cde  cde   cde   cde   e       e         Scab index = scab type x surface area covered by scab x 100/33 The selected potato genotypes showed variable resistance to common scab in the field Correlation of the results from the in vitro bioassay and the field experiments  14 15 Summary   The in vitro bioassay utilizing thaxtomin A as a selective agent  • Revealed differences between potato genotypes in thaxtomin sensitivity • Predicted differences between genotypes in their tolerance to common  scab in the glasshouse and in the field • Could be used in resistance screening programs   16 Acknowledgements University of Helsinki  Department of Applied Biology,   Divisions of Pharmaceutical Biology and Pharmaceutical Chemistry Into Laakso  Tuula Laine Jouko Närhi Lahja Pesonen Kati Takala Anja Weckman    MTT Agrifood Research Finland   Arjo Kangas   Anu Kankaala  Anna Sipilä  Tapio Uotila  Tiina Väyrynen  Charles University, Czech Republic Vladimír Chobot    4.12.2013 17 Thank you! 

Use of Thaxtomin A as a selective agent for screening potato genotypes for resistance to common scab

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