Pear trees become infected with branch and trunk diseases, and the damage hinders high-quality development of the pear industry. In December 2024, symptoms characterized by bark cracking, dark-brown lesions, and conidial masses were observed on the branches of 100 trees of Pyrus pyrifolia cultivar 'Caiyunhong' in a 200 acre orchard in Anning City, Yunnan Province, China. Three representative diseased samples A1-3, were randomly selected for pathogen isolation. Conidial masses from A3 were diluted with sterile water, and spread onto water agar amended with 200 μg/mL cephalosporin, and later transferred to PDA. Diseased branch samples A1 and A2 were cut into ~1 cm2 pieces, sterilized twice with 75% ethanol for 45 s each, rinsed twice with sterile water, and placed on PDA. The above cultures were purified by the hyphal tip and incubated in the dark at 25℃. Eight isolates with identical morphology were obtained, including two from A1, two from A2, and four from A3. Two representative strains, SZ-1 from A3 and SZ-8 from A1, grew at 2.45 and 2.42 cm/d, respectively, forming circular, smooth-margined colonies with white, cottony aerial hyphae and light yellow pigment. The conidia were oblong-ellipsoidal, aseptate, hyaline, smooth and thin-walled, measuring 5.7 to 10.4 × 3.6 to 6.2 μm (mean 7.9 × 4.7 μm, n = 50). The morphological traits of SZ-1 and SZ-8 were consistent with those of Nectria pseudotrichia (Yang et al. 2019). DNA was extracted with a TSINGKE kit. PCR was performed using ITS1/ITS4, Bt2a/Bt2b, and EF1-728F/EF1-986R primers (Carbone and Kohn 1999; Glass and Donaldson 1995; White et al. 1990). The sequences of ITS, EF1-α, or TUB2 from isolates SZ-1 and SZ-8 were identical. SZ-1 sequences were deposited in GenBank (ITS: PX247482; EF1-α: PX216859; TUB2: PX210919). BLASTn analysis revealed that the ITS and TUB2 sequences of SZ-1 had the highest similarities of 98.67% and 98.26% with N. pseudotrichia CFCC 52122, meanwhile the EF1-α sequence similarity was 95.61% with intraspecific variation. The concatenated ITS–EF1-α–TUB2 sequences were aligned using MUSCLE in MEGA 11. Phylogenetic analysis was performed by the maximum likelihood method using the Tamura-Nei model with uniform rates and 1,000 bootstrap replicates. It showed that SZ-1 and SZ-8 clustered together with reference isolates of N. pseudotrichia with 100% bootstrap support. Other species of Nectria were more distant, and two isolates of Thelonectria were used as outgroup. Fruits of P. sinkiangensis 'Korla' were inoculated with 1 × 10⁶ conidia/mL after needle-prick wounding, and incubated at 25°C with a 12-h light/ dark cycle. Fruits developed rot and sunken lesions at 7 dpi. SZ-1 and SZ-8 mycelial plugs were placed on tender shoots and one-year-old branches of original host 'Caiyunhong', and on seedling stems of potted P. betulifolia. Lesions spread rapidly on tender shoots, causing wilting and death at 4 dpi. Conidial masses developed on branches at 14 dpi. Sunken lesions girdled P. betulifolia stems at 15 dpi, causing plant death. Controls inoculated with sterile water and PDA, remained symptomless. The same pathogen was reisolated from all diseased tissues, fulfilling Koch's postulates on 'Caiyunhong', and other species of pear. N. pseudotrichia was the causative agent for pear canker disease and fruit rot. This is the first report of N. pseudotrichia causing canker disease on pear in China. These findings will aid in accurate monitoring and management of this disease to prevent significant damage.
Wu et al. (Mon,) studied this question.