Colletotrichum Horii Causing Fruit Rot of Nutmeg (Myristica Fragrans Houtt.) in Malaysia

Abstract

Nutmeg (Myristica fragrans Houtt.) is widely cultivated in Malaysia, with Penang being the leading state. During field visit in 2022, fruit rot disease was observed in several orchards, significantly reducing nutmeg production. Affected fruits showed black sunken lesions on the surface of nutmeg fruit. To date, this disease has not been reported in Malaysia. A total of 10 nutmeg fruit showing fruit rot disease symptoms were collected from several nutmeg orchards in Penang for fungal isolation. Morphological and molecular approaches, along with pathogenicity assessments, were conducted to determine the causal fungal pathogen. The obtained fungal isolates were identified tentatively as Colletorichum species through morphological characteristics, which was further confirmed as C. horii through molecular analyses using internal transcribed spacer (ITS) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene loci. Phylogenetic analyses using maximum likelihood (ML) and maximum parsimony (MP) methods strongly supported the species identification with high bootstrap value (100%). A total of 32 asymptomatic healthy immature nutmeg fruit were used for pathogenicity test showed disease symptoms similar as observed in the field in artificially wounded fruits, while non-wounded fruits remained asymptomatic, fulfilling Koch’s postulates. This is the first report of C. horii causing fruit rot of nutmeg in Malaysia. These findings provide a foundation for developing effective diseases management strategies to mitigate nutmeg field losses.

Keywords: Colletotrichum horii, nutmeg, Fruit rot, Malaysia