Pecan (Carya illinoinensis) is one of the important economic forest crops widely cultivated in Jiangsu Provinces, China. From August to September in both 2021 and 2022, a foliar blight was observed in 7-ha and 6-ha pecan orchards in Changzhou (31°58'9.6″ N, 119°48'33.84″ E), and Jurong (31°52'15.46″ N, 119°9'24.62″ E), Jiangsu Province. The disease severity was about 32% with 8% incidence on 120 surveyed trees of the two orchards. Typical symptoms were lesions with a dark-brown color, which later became brown. We collected eighteen pecan leaves with typical symptoms in the surveyed pecan orchards and took them back to the laboratory for identification. Small fragments (approximately 9 mm2) from the necrotic borders of infected leaves were surfaced sterilized, plated on potato dextrose agar (PDA) and then incubated in darkness at 25°C. Pure cultures were obtained by single-spore culture. Thirty-three isolates with similar characteristics were obtained from the infected leaves (isolation frequency 85%), and the colonies surface on PDA was ochreous with patchs of olivaceous-yellow and sparse aerial mycelium. Observing from the back of the plate, the colonies were cream-yellow. Two types of single-cell conidia were produced on PDA. Alpha-conidia were 7.4 (range, 5.9 to 8.8) × 2.1 (range, 1.6 to 2.8) μm (n = 100), aseptate, smooth, fusiform, straight and tapering towards both ends. Beta-conidia were 25.1 (range, 19.1 to 36.2) × 1.3 (range, 1.0 to 2) µm (n = 100), filiform, hyaline, aseptate and curved at one end. The morphological features of these isolates agreed with those of Diaporthe sp. (Gomes et al. 2013; Gao et al. 2017). To further identify the isolates, the regions of internal transcribed spacer (ITS, OR214967 to OR214969), calmodulin (CAL, OR228558 to OR228560), translation elongation factor 1-α (EF1a, OR228561 to OR228563), histone H3 (HIS, OR228564 to OR228566), and beta-tubulin 2 (TUB2, OR228567 to OR228569) were amplified and sequenced from genomic DNA for the three representative isolates (LSM1, LSM2 and LSM3), respectively (Gomes et al. 2013). Multilocus phylogenetic analysis revealed that the three isolates and D. pseudophoenicicola were clustered in the same clade. Based on the results of morphological and molecular analysis, these isolates were identified as D. pseudophoenicicola. The pathogenicity of three isolates were tested on leaves of pecan seedlings. The conidial suspension (1 × 105 conidia/ml) of each isolate was sprayed evenly on the surface of leaves of three healthy seedlings. Sterilized distilled water was used for negative controls. Finally, all inoculated plants were kept in a greenhouse at 28°C under 100% relative humidity. Two weeks after inoculation, the inoculated plants developed symptoms similar to those of the original diseased plants, while controls remained asymptomatic. D. pseudophoenicicola were re-isolated from from inoculated plants. The pathogenicity experiment was repeated three times. Previously, D. pseudophoenicicola has been reported to cause stem-end browning disease in ripe mango (Takushi et al. 2016; Xu et al 2022). To our knowledge, this is the first report of D. pseudophoenicicola causing leaf blight on pecan . This study provides important information for developing effective pecan disease management practices.
Keywords: Carya illinoinensis; Diaporthe pseudophoenicicola; Leaf blight; Pathogenicity.