First Report of Epicoccum sorghinum Causing leaf spot on Bothriochloa ischaemum in Malaysia.

Abstract

Bothriochloa ischaemum (family Poaceae) is a perennial weed that can be found in borders of agricultural fields, pastures and roadsides in Malaysia. B. ischaemum is an important phytoremediation species in copper tailings dams (Jia et al. 2020). In December 2021, chlorotic spots with brown halos were observed on leaf samples of B. ischaemum with an incidence of approximately 80% in Penampang, Sabah province (5°56'50.4"N, 116°04'32.8"E). On older leaves, the spots coalesced into larger chlorotic spots. Small pieces (5 x 5 mm) of infected leaves collected from three plants were excised, and then surface sterilized according to Khoo et al. (2022). The fungus was isolated (one isolate was obtained) and cultured on potato dextrose agar (PDA) at 25°C. After 3 days, the colony had cottony aerial mycelia with light purple concentric rings appearing on the underside of the colony. Chlamydospores were produced, either unicellular or multicellular. Conidia were unicellular, hyaline, oval, and were 3.7 to 5.1 x 1.8 to 2.6 μm (n=20). Pycnidia were spheroid, and were 66.4 to 115.3 x 43.1 to 87.4 μm (n=20). Genomic DNA was extracted from fresh mycelia of the fungus based on the extraction method described by Khoo et al. (2022). Amplification of the internal transcribed spacer (ITS) region and large subunit (LSU) of rDNA, and actin (ACT), tubulin (TUB) and RNA polymerase II second largest subunit (RPB2) genes was performed using ITS1/ITS4, LR0R/LR7, ACT512F/ACT783R, T10/Bt2b and RPB2-5F2/RPB2-7cR primers, respectively (O'Donnell and Cigelnik, 1997; Liu et al. 1999; Sung et al. 2007; Chen et al. 2021). The PCR products were sequenced at Apical Scientific Sdn. Bhd.. Sequences were deposited in GenBank as OM453926 (ITS), OM453925 (LSU), OM451236 (ACT), OM451237 (TUB) and OM863567 (RPB2). Sequences of our isolate had 100% homology to ITS of isolate UMS (OK626271) (507/507 bp), LSU of isolate UMS (OM238129) (1328/1328 bp), ACT of isolate CZ01 (MN956831) (275/275 bp), TUB of isolate BJ-F1 (MF987525) (556/556 bp) and RPB2 of isolate HYCX2 (MK836295) (596/596 bp) sequences. Phylogenetic analysis was performed using the maximum likelihood method based on the general time reversible model with a gamma distribution and invariant sites (GTR + G + I) generated from the combined ITS, TUB, LSU and RPB2 sequences, indicating that the isolates formed a supported clade to the related Epicoccum sorghinum type sequences. Morphological and molecular characterization matched the description of E. sorghinum (Li et al. 2020). Koch's postulates were performed by spray inoculation (106 spores/ml) on the leaves of three healthy B. ischaemum plants, using isolate BPL01, while sterilized water was sprayed on three additional B. ischaemum which served as the control. Symptoms similar to those occurred after 6 days post inoculation. No symptoms occurred on controls. The experiment was repeated two more times. The reisolated pathogen was morphologically and genetically identical to E. sorghinum. E. sorghinum was reported previously on Brassica parachinensis (Yu et al. 2019), Camellia sinensis (Bao et al. 2019), Myrica rubra (Li et al. 2020), Oryza sativa (Liu et al. 2020) and Zea mays (Chen et al. 2021) in China. To our knowledge, this is the first report of E. sorghinum causing leaf spot on B. ischaemum in Malaysia. Our findings expand the geographic range and host range of E. sorghinum in Malaysia. B. ischaemum which is a weed in agricultural fields is a host of the pathogen and therefore could be a potential threat to Brassica parachinensis, Camellia sinensis, Oryza sativa and Zea mays in Malaysia. Weed management could be an effective way to eliminate inoculum sources of E. sorghinum.