In June 2024, panicle rot was observed on rice (Oryza sativa L. subsp. japonica cv. Nipponbare) in Hangzhou, Zhejiang Province, China. Disease incidence reached approximately 50% in a greenhouse at Zhejiang University and was similar in a rice germplasm nursery in Yuhang District. Affected panicles were covered with dense black mycelial growth, and some grains appeared partially shriveled with poor filling. Symptomatic panicles were surface-sterilized with 75% ethanol, and diseased tissue pieces (approximately 3 mm 2 ) were plated on potato dextrose agar (PDA) at 25°C. After 3 days, hyphal tips were transferred to fresh PDA and incubated at 25°C in the dark for 20 days. Fungal colonies with Cladosporium-like morphology were isolated from 40% of samples (n = 15). Single hyphal tip cultures of two putative isolates were deposited and stored at the Agricultural Experiment Station of Zhejiang University. Conidia of both isolates were unicellular and ellipsoidal. The conidial size of ZJUP1413 measured 1.18 to 4.31 × 1.13 to 8.86 µm (mean = 2.37 ± 0.62 × 4.28 ± 1.46 µm; n = 100). These morphological characteristics were consistent with those of Cladosporium species (Yang et al. 2023). Genomic DNA was extracted and ITS, act, and tef1 regions were sequenced. BLAST analyses revealed the highest nucleotide identity with reference strain GUCC 21206 of C. pruni-salicina (ITS: 99.78%, OP852683; act: 100%, OP863092; tef1: 99.60%, OP859041). Sequences were deposited in GenBank (ITS: PX612559, act: PZ213613, tef1: PZ213614). Pathogenicity of isolate ZJUP1413 was evaluated on O. sativa cv. Nipponbare in a greenhouse (28°C, 80% relative humidity, 12-h photoperiod). After cultivation in potato dextrose broth for 7 days, a conidial suspension was prepared, and the spore concentration was adjusted to approximately 1 × 10⁶ conidia/ml. The suspension was sprayed onto all panicles of 12 heading rice plants, with 12 water-sprayed plants as controls. Ten days after inoculation, 100% of the inoculated plants developed dense dark mycelial growth and sporulation on at least one panicle, resembling those observed in the field. Control plants remained symptomless. The pathogen was reisolated from the symptomatic panicles and confirmed as C. pruni-salicina morphologically and molecularly. C. pruni-salicina was not isolated from the uninoculated control plants, fulfilling Koch's postulates. C. pruni-salicina was initially reported in Guizhou Province, China, isolated from a leaf of Prunus salicina (Yang et al. 2023). While Fusarium and Alternaria spp. predominantly cause rice panicle rot in China (Wang et al. 2021; Huang et al. 2011), Cladosporium species typically cause leaf spots and postharvest rot (Huang et al. 2013; Xie et al. 2022). This is the first report of C. pruni-salicina causing panicle rot on rice in China, contributing to improved understanding of potential fungal threats to rice production under greenhouse or nursery conditions.
Zhang et al. (2026) studied this question.