Diagnosis of Dieback Disease of the Nutmeg Tree in Aceh Selatan, Indonesia

Abstract

Effective control disease measures require a great deal of knowledge about the pathogen, which is also applied to dieback disease of the nutmeg tree in Aceh Selatan District, Province of Aceh, Indonesia. The objectives of this study were to identify the causal agent of dieback disease on a nutmeg plantation and to assess the effect of drought stress on the development of dieback disease. Pathogen identification was carried out by observing the symptoms of infected plants, morphological characters of the isolated pathogens, Koch’s postulates, and molecular analysis and pure pathogen cultures. The samples were taken from an infected part of the nutmeg plant (twigs, stems, and roots) in 6 subdistricts at the center of the nutmeg plantation in Aceh Selatan. Koch's postulates were performed by using the mycelia of pathogens on 1-year-old nutmeg seedlings. Drought stress was simulated everyday, and then once every 2 weeks, to study the effect of drought stress on dieback. The results showed that there were 4 genera of fungal pathogens (Botryodiplodia theobromae, Fusarium solani, Graphium euwallaceae, and Rigidoporus microporus) out of 6 fungi associated with dieback disease. However, B. theobromae Pat. turned out to be the dominant fungi associated with dieback on the nutmeg tree in Aceh Selatan. Drought stress was proven to be a predisposing factor for explaining this problem epidemic in Aceh Selatan.