A Report of Fungi Associated With the Scarred-Scabbed Symptoms on Maprang (Bouea macrophylla Griffith) in Eastern Thailand

Abstract

Maprang, commonly known as a marian plum or plum mango (Bouea macrophylla Griffith), is an edible tropical fruit belonging to the family Anacardiaceae. It is grown extensively throughout ASEAN countries including Indonesia, Malaysia, Thailand, and the Philippines (Dechsupa et al., 2019;Nguyen et al., 2020). There are three varieties of maprang grown in Thailand, including maprang prieyo (sour maprang), maprang wan (sweet maprang), and mayong chid (sweet maprang with bitter flavor) (Dechsupa et al., 2019).During the last few years, the scarred-scabbed symptoms on maprang fruits have been observed in Rayong Province, which is located on the coastline of eastern Thailand. Disease symptoms include numerous tiny dark spots and subsequent development of scarred-scabbed areas on the fruits. The scarred-scabbed areas can distort the mature fruits. Therefore, the scarred-scabbed symptoms are aesthetic-related problems that can reduce the value of the fruit in markets. The etiology of the disease symptoms in Rayong Province is unclear. The possibility of the etiology has been ascribed to the wounds created by feeding activities of chili thrips (Scirtothrips dorsalis Hood) associated with an anthracnose Colletotrichum gloeosporioides Penz. fungus. However, the microbiological study has yet to be identified the cause of the disease.Thirty samples of diseased fruits were collected in January 2023 from different orchards in Rayong Province, Thailand (Figure 1). Every orchard was routinely sprayed with abamectin, cypermethrin, and profenopos insecticides to control the chili thrips. The scarred-scabbed areas of each fruit sample were cut into 1 × 1 cm fragments, after which the surfaces were sterilized with 0.5% (v/v) of sodium hypochlorite solution for three min, and subsequently rinsed three times in sterilized water, similar to the method used by Chantarasiri et al. (2021). The samples were plated on dichloran rose bengal chloramphenicol (DRBC) agar as a fungal selective medium and incubated at 30 °C for seven days in the dark. The emerging fungal mycelia of each colony were inoculated on potato dextrose agar (PDA) and incubated for culture purification under the aforementioned conditions. All isolated fungi were primarily categorized according to their colony and conidia morphology.Genomic DNA of the representative fungal isolates was extracted from the mycelia using the GF Fungus DNA Extraction Kit (Vivantis, Malaysia), and the internal transcribed spacer (ITS) regions were PCR amplified using ITS1/ITS4 universal primers (White et al., 1990). The PCR was carried out using the OnePCR reaction mixture (Bio-Helix, Taiwan). The conditions of PCR were conducted according to Planonth and Chantarasiri (2022).