Isolation and Structure Identification of Phytotoxins from Lasiodiplodia theobrorme, the Cause of JAVA Black Rot of Sweet Potato

고구마 검은썩음병균(Lasiodiplodia theobromae)으로부터 식물독소의 분리 및 구조

Lasiodiplodia theobrorme is a pathogen of Java black rot on sweet potato. This fungus infects the tuberous root during storage after harvest. Invasion of the fungus results in the expansion of necrosis sites into the tuberous roots. The resultant necrotic symptom of the tissue is also induced by application of acetone extract of the fungus growing on potato sucrose agar (PSA) culture. The active principles to induce the necrosis are purified from the acetone extract as follows. After evaporation of hexane-benzene-EtOAc (1:2:1, v/v/v) the extract was fractioned on silica gel column, using a solvent gradient system from n-hexane to EtOAc and then to MeOH. The active fractions were purified with HPLC on Nucleosil 50-5 column by eluting n-hexane to EtOAc. Their structures are established by using spectroscopic techniques and synthesis to 4-hydroxymellein and mellein, respectively. Application of small amount of these compounds induce expansion of the necrotic symptom into the tissue and accumulated ipomeamarone. Conclusively, these compounds acted as phytotoxins (inducing necrosis) and as elicitors (eliciting the phytoalexin).

고구마 검은 썩음병균(L. theobromae)의 PSA배양물의 acetone추출물을 고구마 괴근에 처리하면 갈변이 유도된다. 공시균의 배양물로부터 갈변유도 활성물질을 분리 정제하여 화학구조를 결정하고 각각 4-hydroxymellein과 mellein으로 동정하였다. 화학합성에 의하여 천연 mellein의 상대구조는 (R)-(-)-mellein임을 입증하였다. 각 화합물은 $50{\sim}100{\mu}g$ 고구마에 접종하였을때 농도 의존적으로 갈변을 유도하였다. 또한 이들 화합물들이 고구마의 phytoalexin으로 알려져 있는 ipomeamarone의 생합성을 유도하는 elicitor로써 작용하고 있음을 증명하였다.