Resistance of red clover (Trifolium pratense) to the root parasitic plant Orobanche minor is activated by salicylate but not by jasmonate.
OBJECTIVE
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.


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.
Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan.
Dai
D
Kusumoto
Yaakov
Y
Goldwasser
Xiaonan
X
Xie
Kaori
K
Yoneyama
Yasutomo
Y
Takeuchi
Koichi
K
Yoneyama
D003517:Cyclopentanes / Q000494:pharmacology; D031672:Orobanche / Q000502:physiology*; D054883:Oxylipins; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000469:parasitology; D020156:Salicylic Acid / Q000494:pharmacology*; D036226:Seedlings / Q000254:growth & development / Q000469:parasitology; D029921:Trifolium / Q000166:cytology / Q000187:drug effects* / Q000469:parasitology*
D003517:Cyclopentanes; D054883:Oxylipins; C011006:jasmonic acid; D020156:Salicylic Acid