Characterization of the Pathogenic Fungus Phytophthora palmivora, the Cause of Stem Rot Disease in Durian (Durio zibethinus Murray) in Buleleng Regency, Bali

Abstract

Durian (Durio zibethinus Murray) is a horticultural commodity with high economic value in Buleleng Regency. However, its development faces obstacles from stem rot disease, which can reduce productivity and even cause plant death. This study aims to identify the pathogen causing durian stem rot through isolation of pathogenic fungi, pathogenicity tests, morphological characterization, and molecular and phylogenetic analysis. Samples were taken from symptomatic durian plants in the production center of Buleleng Regency. Six isolates were successfully isolated from plants with stem rot symptoms, namely Srt001, Srt002, Srt003, Kbt001, Bsb001, and Swn001, and then tested for pathogenicity on durian seedlings of the Otong variety. Only isolate Srt003 re-emerged with typical symptoms of reddish-brown gummosis on the stem 30 days after inoculation. Identification of morphological characters showed that isolate Srt003 formed grayish-white to transparent colonies with a stellate-radiate pattern and hyaline, coenocytic hyphae. Sporangia are ovoid to ellipsoid, some nearly globose, papillated, caducous, and measure approximately 40–60 × 21–46 µm. Sequence analysis of the rDNA Internal Transcribed Spacer (ITS) region and phylogenetic analysis confirmed that isolate Srt003 has a sequence identity of up to 99.60% with Phytophthora palmivora. The results showed that P. palmivora is a pathogen causing durian stem rot in Buleleng Regency. This study is the first report of P. palmivora causing stem rot in Buleleng, Bali, based on morphological and molecular approaches.