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Diversity of Fungi Associated with Vascular Streak Dieback (VSD) Disease on Cacao Plantation in Special Region of Yogyakarta Province
Thesis Abstract:
Cacao (Theobroma cacao L.) is one of the most important estate crops in Indonesia. Recently, Indonesia is the third largest cacao producer in the world after Ivory Coast and Ghana. Vascular Streak Dieback (VSD) is one of the major diseases of the cacao crop in Indonesia which caused by a fungus, Oncobasidium theobromae. In the field, the causal agents of this disease were recognized as other fungi in some areas and on cacao genotypes. The objective of this study is to identify morphological and molecular characterization of the fungal pathogens associated with VSD disease in cacao plantation in Yogyakarta Special Province. The activities in this study included survey, sampling, isolation, in-vitro pathogenicity test, morphological and molecular identification. This study was conducted in the Laboratory of Plant Disease, Faculty of Agriculture, UGM, Yogyakarta. Survey and sampling in the field were conducted at 16 locations of cacao plantations in Yogyakarta Special Province which included Regencies of Gunungkidul, Kulon Progo, Sleman, and Bantul. There were 88 fungal isolates collected which were obtained from cacao stems and petioles with VSD infected from the field. The result of the pathogenicity test in vitro was derived in 4 groups. In group 1, there were 12 fungal isolates, 20 fungal isolates in group 2, 14 fungal isolates in group 3, and 42 fungal isolates grouped in group 4. There were 32 fungal isolates selected. Based on colony morphology, fungal isolates were divided into three clusters. Cgn2b1 and Cgn2b2 isolates in cluster I showed similar character with 100% similarity. Kb1d1, Kb2b2, Kb2b5, kb2b6, Cgn2d3, and Dl1b2 isolates in cluster II also showed similar character with 100% similarity based on colony morphology. There were 24 isolates identified based on microscopic observation of conidial morphology either macrospora or microspora. They were assumed into genus Fusarium, Colletotrichum, Pestalotiopsis, and Lasiodiplodia. The PCR test showed that DNA from all isolates selected could be amplified at range 550-700 bp using universal primer pair ITS1-ITS4. The pathogen, which was associated with VSD dieback on cacao in Yogyakarta were Lasiodiplodia theobromae, Fusarium decemcellulare, F. solani, F. proliferatum, Colletotrichum siamense, Diaporthe ueckerae, D perseae, Pestalotiopsis microspora, and Corynespora cassiicola.