Judul: Identification and Pathogenicity of Primary Fungi Causing Dieback Disease on Jabon Seedlings (Anthocephalus cadamba (Roxb.) Miq).
Abstrak: Jabon (Anthocephalus cadamba (Roxb.) Miq) is indigenous plant of Indonesia which is currently attracted by many people due to able provide benefits, both economical and ecological. Along with its development and cultivation, the market demand of jabon will get increase. Propagation of jabon potentially facing diseases disorders in the nursery area. This is because of available seedlings in the nursery area have the potential to be a host for the pathogens and the succulent seedling conditions are relatively vulnerable to disease attacks. The disease symptoms are often found in the jabon nursery areas and potentially leading to death of seedlings are dieback diseases. This study was conducted with the aim to isolate and identify the fungal pathogen cause of dieback diseases on jabon seedlings, determine the primary cause of dieback diseases and test the virulence levels of those isolates, and to study the mechanisms of pathogen infection and host defense mechanisms to against pathogens. The study consisted of the observation of symptoms and sampling diseased plants from the nursery locations, isolation and identification of fungi, pathogenicity assay of fungal isolates, analysis of pectinase and cellulase activities produced by fungal pathogens, and analysis of peroxidase activity on jabon. Based on observation of symptoms at the nursery sites, jabon seedlings infected dieback disease had necrotic symptoms on stems or leaves, withered or shriveled on stems. A total of 21 isolates of the fungus could be isolated from diseased plants showed necrotic symptoms at the plant tips. Identification based on morphological characters, these isolates were known as Botryodiplodia spp. as much as 9 isolates, Fusarium spp. 9 isolates, Colletotrichum sp., Curvularia sp., and Pestalotiopsis sp. each 1 isolate. Based on Koch's postulates, the fungal isolates which were pathogenic to jabon were Botryodiplodia spp., Fusarium spp., and Colletotrichum sp.. The fungus suspected as the primary cause of the dieback disease was Botryodiplodia spp. This is because of Botryodiplodia spp. isolates inoculation could produce identical symptoms with dieback symptoms that occur naturally in the field. The results of pathogenicity assay of 5 Botryodiplodia spp. isolates showed that these isolates had different degrees of pathogenicity. It could be seen from the percentage of disease severity caused. Based on Duncan's multiple interval test (α 5%) on the disease severity, could be seen that 3 of 5 Botryodiplodia spp. isolates tested were highly virulent to jabon seedlings, while the others were less virulent. The mechanisms used by Botryodiplodia spp. isolates to infect the hosts presumably performed using mechanical and biochemical forces. These were showed by the appearance of necrotic symptoms on unwounded inoculation sites and the pectinase and cellulase activities detectable from Botryodiplodia spp. isolates cultured in CMS (Corn Meal Sand) media. Pectinase activity produced by Botryodiplodia spp. isolates was ranging from 18.131 to 26.083 U ml-1, whereas cellulase from 0.014 to 0.023 U ml-1. The defense mechanism of jabon plant against pathogen infection, one of them was vii performed by produce peroxidase which plays role of lignification process and secondary metabolite compound formation. Peroxidase activity detectable on the jabon plants after pathogen inoculation was ranging from 0.0006 to 0.0012
Keyword: Botryodiplodia spp., Fusarium spp., Koch’s postulate, necrotic, nursery