First Report of Internal Browning of Jackfruit ( Artocarpus heterophyllus cv. 'Malaysia No. 1') Caused by Tatumella citrea in China

Jackfruit (Artocarpus heterophyllus), one of the largest fruits in the world, is widely cultivated in tropical and subtropical regions of China, including Hainan, Guangdong, Yunnan, Guangxi, and Fujian provinces (Hu and Wang, 2016). On December 24, 2025, symptoms of internal browning disease were observed on jackfruit cv. ‘Malaysia No. 1’ in a commercial orchard in Yuanjiang County, Yuxi City, Yunnan Province (23.534224°N, 102.087571°E). Symptoms included brown necrotic lesions on the outer rind. Cross-sections revealed extensive browning of the fruit fibers (perianth) and core, while the individual fruit bulbs remained visually normal. The disease incidence reached approximately 70% in the affected blocks. To isolate the causal agent, tissue samples (approx. 5 mm³) were excised from the margin of symptomatic fruit cores and fibers from ten diseased fruits. Samples were surface-sterilized in 3% hydrogen peroxide for 3 min, rinsed twice with sterile distilled water, and plated on Nutrient Agar (NA). Plates were incubated at 28°C for 24 h. Single colonies were purified by streaking and incubated for an additional 24 h. Ten isolates with identical morphology were obtained from the ten diseased fruits, and one representative isolate was designated as Tc-XSBN-2025-1224-01. Resulting colonies were creamy-white, mucoid, oval-shaped, and emitted a distinct alcoholic odor. Microscopic examination revealed Gram-negative, ellipsoidal cells measuring approximately 3–8 μm in width and 5–15 μm in length. Genomic DNA was extracted from 48-h cultures. The near-full-length 16S rRNA gene (~1,500 bp) was amplified using primers 16S-27F (5′-AGAGTTTGATCMTGGCTCAG-3′) and 16S-1492R (5′-TACGGYTACCTTGTTACGACTT-3′) (Danneels and Carlier 2023; Ma et al. 2019). The resulting sequence (Accession No. PX969701) showed 99.85% identity to Tatumella citrea strain JCM 8882 (Accession No. AB907782.1) and other T. citrea strains (e.g., DSM 13699, LMG 22049) in BLASTn analysis. Phylogenetic analysis using the Maximum Likelihood method in MEGA software confirmed that the isolate (Tc-XSBN-2025-1224-01) clustered tightly with T. citrea reference strains with 100% bootstrap support, distinct from related species such as T. ptyseos, T. saanichensis, and outgroups Citrobacter, Enterobacter, and Kluyvera. To fulfill Koch’s postulates, pathogenicity tests were conducted on healthy, 3-month-old ‘Malaysia No. 1’ jackfruits at the same orchard. Bacterial suspensions (1 × 10⁶ CFU·ml⁻¹) of isolate Tc-XSBN-2025-1224-01 grown in LB broth for 24 h were injected (1 ml per site) into the fruit flesh using a sterile syringe. Control fruits were injected with sterile distilled water. Each treatment included six replicates. Seven days post-inoculation, fruits inoculated with T. citrea developed symptoms identical to those observed in the field, including internal browning and alcoholic fermentation odor. Control fruits remained asymptomatic. The bacterium was re-isolated from symptomatic tissues and confirmed as T. citrea based on colony morphology and 16S rRNA gene sequencing. Tatumella citrea has previously been reported as both a saprophyte and an opportunistic pathogen in various hosts (Noguera 2022). To our knowledge, this is the first report of T. citrea causing internal browning disease on jackfruit in China. This finding expands the known host range of T. citrea and provides a basis for developing effective management strategies for this emerging disease.