First Report of Bacterial Shot Hole Disease of Peach Caused by Pseudomonas oryzihabitans in China

Peach [Prunus persica (L.) Batsch] is an an important fruit tree in China. Bacterial shot hole is a common foliar disease of peach that affects tree vigor and yield. In the summer of 2024, an occurrence of bacterial shot hole, with an incidence rate of 10%–20%, was observed in a peach orchard of about 2 ha in Nanbianshan Town, Lingui District, Guilin City, Guangxi Zhuang Autonomous Region of China. Lesions were reddish-brown with yellow halos; centers dried and fell out, forming typical shot-hole symptoms. To identify the causal agent, leaves with typical symptoms were collected. After surface sterilization with 75% ethanol and rinsing with sterile water, lesion margin tissues were ground in sterile water and streaked onto nutrient agar (NA) at 28°C for 24–48 h. Dominant colonies with uniform morphology were selected and purified. On NA medium, the purified colonies were initially pale yellow, later yellow, circular, smooth, flat, opaque, and easy to pick. The isolate was Gram-negative, short rods, and gave a negative hypersensitive response on tobacco. It could utilize glucose, arabinose, maltose, mannitol, sucrose, xylose, and Simmons citrate; it was positive for catalase, and negative for arginine dihydrolase, nitrate reduction, ornithine decarboxylase, lysine decarboxylase, arginine decarboxylase, urease, hydrogen sulfide production, indole, esculin, ONPG, and oxidase. For molecular identification, 16S rRNA and gyrB genes were sequenced using primer pairs 27F/1492R and UP1/UP2r (Yamamoto et al. 1995). A phylogenetic tree constructed in MEGA11 using the neighbor‑joining method based on the concatenated sequences of the 16S rRNA (GenBank PZ517484 and PZ520133) and gyrB (PZ529016 and PZ529017) showed that the isolate clustered together with Pseudomonas oryzihabitans HN6 (GenBank PQ374171 and PQ393140) in the same clade. Pathogenicity was tested by injecting a bacterial suspension (10⁸ CFU/mL) into detached and attached peach leaves; sterile water and Xanthomonas arboricola pv. pruni 9-4 served as negative and positive controls, respectively. Detached leaves were incubated at 25°C and relative humidity above 85%, while attached leaves were bagged to maintain humidity. After 2 days, inoculated leaves developed brown lesions, positive controls showed water-soaked spots, and negative controls remained healthy. Additionally, spray inoculation on attached leaves with micro-wounds (created by rubbing with quartz sand) using the same suspension caused reddish-brown spots after 4 days, which worsened over time. All leaves inoculated by injection (both detached and attached) and by spray inoculation developed symptoms. The same pathogen was re-isolated from all symptomatic inoculated tissues, and its morphological and molecular characteristics were identical to those of the original inoculated strain, thereby fulfilling Koch’s postulates. In recent years, P. oryzihabitans has been increasingly recognized as a plant pathogen, causing diseases such as rice panicle blight and grain discoloration (Hou et al. 2020), chili pepper leaf spot (Du et al. 2025), and walnut leaf spot (Huai et al. 2024). To our knowledge, this is the first report of P. oryzihabitans causing bacterial shot hole on peach, expanding its host range and providing a basis for disease surveillance and control.