AOBPreview originally published online on July 27, 2007
Annals of Botany 2007 100(3):537-544; doi:10.1093/aob/mcm148
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Resistance of Red Clover (Trifolium pratense) to the Root Parasitic Plant Orobanche minor is Activated by Salicylate but not by Jasmonate
1 Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan
2 R.H. Smith Institute of Plant Sciences & Genetics in Agriculture, Faculty of Agriculture, Food & Environmental Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel
3 United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan
* For correspondence. E-mail yoneyama{at}cc.utsunomiya-u.ac.jp
Received: 12 February 2007 Returned for revision: 21 May 2007 Accepted: 1 June 2007 Published electronically: 27 July 2007
Background and Aims: Obligate root holoparasites of the genus Orobanche attack dicotyledonous crops and cause severe losses in many parts of the world. Chemical induction of plant defence systems such as systemic acquired resistance was proposed to be an available strategy to control the root parasite, but the detailed mechanisms involved have not been clarified. The aim of this study was to elucidate the effects of salicylic acid (SA), jasmonic acid (JA) and their analogues on resistance of red clover to Orobanche parasitism.
Methods: Roots of red clover grown in plastic chambers were applied with SA, S-methyl benzo[1,2,3]thiadiazole-7-carbothioate (BTH), methyl jasmonate (MeJA) and n-propyl dihydrojasmonate (PDJ), and then were inoculated with O. minor seeds. Attachments of the parasite were observed after 5 weeks.
Key Results: SA and BTH, inducers of SA-mediated defences, significantly reduced the number of established parasites by more than 75 %. By contrast, MeJA and PDJ, inducers of JA-mediated defences, did not affect parasitism. The reduction in the number of established parasites by SA and BTH was due to the inhibited elongation of O. minor radicles and the activation of defence responses in the host root including lignification of the endodermis.
Conclusions: These results suggest that SA-induced resistance, but not JA-induced resistance, is effective in inhibiting Orobanche parasitism and that the resistance is expressed by the host root both externally and internally.
Key words: Endodermis, haustorium inducing signal, induced resistance, jasmonic acid, lignification, Orobanche minor, root parasitic plant, salicylic acid, Trifolium pratense (red clover)