First Report of Phyllachora sp. Causing Tar Spot on Seashore Paspalum in South China

Abstract

Seashore paspalum is an indigenous, warm-season turfgrass that is often used on golf courses, sport fields, and other recreational sites, especially where salt is an issue (Guo et al. 2016). One hundred forty-six accessions or cultivars collected from south China and the United States currently are planted in the Danzhou campus of Hainan University. In 2017, there was an outbreak of typical tar-spot symptoms on leaves of 94 accessions or cultivars of seashore paspalum. The tar spots, 0.3 to 1.5 mm in diameter, were composed of irregular brown spots surrounded by yellowish halos on the infected leaves. Pseudostromata were subglobose with 0.3 to 1.5 mm diameter, slightly papillate, epiphyllous, shiny black, and immersed in the host leaves. Perithecia (268 to 320 μm in diameter) had paraphyses and asci (80 to 110 × 11 to 17 μm) with eight ascospores (5.5 to 8.5 × 8 to 13 μm). Ascospores were ellipsoid, single celled, hyaline, with a central concave depression present or absent. Morphologically, the pathogen was a member of Phyllachorales (Dayarathne et al. 2017). Total DNA from leaf spots was extracted from three seashore paspalum accessions: SP17, SP40, and SP64. The rDNA internal transcribed spacer (ITS) sequences were amplified with the primer pair ITS1f (5′-CTTGGTCATTTAGACGAAGTAA-3′) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′). The results showed that three ITS sequences, 511 bp, were totally identical, and the ITS sequence was deposited in NCBI (MG897306). BLAST analysis revealed that the ITS sequence displayed no high similarity with known Phyllachora species and showed 89% identity with Phyllachora sp. (MG881848.1) and 88% identity with Phyllachora sp. (MG881846.1), confirming that the pathogen was Phyllachora sp. To verify the pathogenicity of the pathogen, healthy stolons of three accessions (SP17, SP40, and SP64) were planted in sterilized sand in an incubation box, which was kept for 2 weeks to confirm that the plants were healthy and without disease. Leaves were then inoculated by a sterilized toothpick with ascospores from mature stromata of infected seashore paspalum planted in the Danzhou campus of Hainan University. Two weeks after inoculation, 80% of inoculated plants showed symptoms of disease, and the fungus from the inoculated leaves was morphologically and molecularly identical to the samples collected in the field. Controls remained without tar-spot symptoms. Tar spot has been reported on several plant species (McCoy et al. 2018); however, this is the first report of Phyllachora sp. on seashore paspalum in south China.