<i>P</i> <i>araphaeosphaeria huizhouensis</i> sp. nov. Causes Leaf Blight of <i>Pandanus tectorius</i> in China

Screw pine (Pandanus tectorius; Pa. tectorius) is traditionally used as a medicinal plant for treating stomach spasms, headaches, and arthritis in Southeast Asia (Anirudhan et al. 2023). In September 2024, leaf blight on this plant was detected in Huizhou City, Guangdong Province, China. Disease incidence reached ~70% in the 100 m² survey area. Initial symptoms appeared as yellow spots, which later developed into brown lesions with halos. Lesions later became elongated and irregular, with pale brown to gray centers and reddish-brown margins with tapered ends (15 to 120 × 5 to 15 mm). Black fruiting bodies were observed at the centers of the lesions. Three isolates (MBSZU 25-006 to 25-008) were obtained and identified as Paraphaeosphaeria huizhouensis sp. nov. T. Thitla, S. Hongsanan, & N. Xie sp. nov. (MycoBank number: MB857540) based on morphological and phylogenetic analyses. The holotype (SZU25-008) and ex-type living culture (MBSZU 25-008) were permanently preserved in a metabolically inactive state in the Herbarium (SZU) and the Culture Collection of Microbial Shenzhen University (MBSZU), Shenzhen University, China. Morphologically, colonies on potato dextrose agar (49–51 mm) and malt extract agar (54–57 mm) after 7 days at 25 °C were white on both surfaces. Conidiomata (100 to 400 × 90 to 380 µm) were pycnidial, immersed, globose to subglobose, dark brown to black and occurred as solitary or aggregated. The conidiomatal wall (14 to 24 µm wide) consisted of pale brown pseudoparenchymatous cells, cells towards the inside hyaline, arranged in a textura angularis. Conidiogenous cells (4 to 8 × 2 to 5.5 µm, L/W ratio = 1.81) were phialidic, hyaline, ellipsoidal to obovoidal, lining the inner cavity. Conidia (4.5 to 8 × 2.5 to 4.5 µm, L/W ratio = 1.79) were subglobose to ellipsoid, aseptate, hyaline to light brown, with small oil-droplets and smooth walls. Maximum likelihood and Bayesian inference analyses were performed on LSU+ITS+SSU+tub2 sequences, which were amplified with primers LR0R/LR5, ITS4/ITS5, NS1/NS4, and Bt2a/Bt2b, respectively (Tennakoon et al. 2022). The new species cluster as a basal clade to P. angularis, P. brachiariae, P. burbidgeae, P. jaguarinae, P. michotii, P. pilleata, and P. sorghi (BS = 88%, PP = 0.96). However, the new species differs by its aseptate conidia and ellipsoidal to obovoidal phialidic conidiogenous cells. Phylogenetic analyses and nucleotide comparisons further confirm that it represents a distinct species. Pathogenicity test was conducted by inoculating 7-day-old fungal agar plugs onto healthy, surface-sterilized Pa. tectorius leaves. Both wounded and unwounded leaves were tested. Sterile agar plugs were used as the control. The plants were kept at 25 °C and 90% relative humidity. After 3 days, yellow halos appeared in both treatments. Subsequently, circular to ellipsoidal pale brown lesions with reddish brown margins and yellow halos were observed in both treatments after 7 days. Circular lesions may result from fungal growth at the inoculation site and later extend along the leaf veins. The lesion sizes were 6 to 11 × 5 to 7 mm (8.8±1.8 × 5.8±0.8; wounded) and 5 to 6 × 3 to 4 mm (5.4±0.5 × 3.6±0.5; unwounded). The controls showed no symptoms. The pathogen was re-isolated from disease lesion and confirmed by morphology and DNA sequencing, fulfilling Koch's postulates, while undetected in control. This study is the first to report P. huizhouensis causing leaf blight in Pa. tectorius and supports epidemiological research.