The Mexican yam bean (Pachyrhizus erosus L. Urban), a high-yielding leguminous root crop with good nutritional value and economic potential as a field crop, is widely cultivated in southern China (Han et al. 2023; Ravi et al. 2025). From September to November 2025, plants showing floral abnormalities, phyllody, proliferation of axillary shoots with shortened internodes, and stunting were found in a farmer’s field at Baihou District (24°17′50. 489″N, 116°46′23. 916″E) and Dapu County, Meizhou City, Guangdong Province, China. These disease symptoms, suspected to be induced by phytoplasma, had an infection rate of about 30% in the field, causing a yield loss of approximately 20%. For further investigation, total DNA was extracted from fresh leaves of ten symptomatic and four asymptomatic samples using a Plant Genomic DNA Purification Kit (DP305; Tiangen; Beijing; China). Conventional nested PCR was performed using primer pairs P1/P7 followed by R16mF2/mR1 (Lee et al. 1993), and amplified a fragment of the expected size only from the symptomatic samples. The phytoplasma strain was designated as GDDPPE2502. The PCR products were sequenced, and a representative nucleotide sequence of 1, 410 bp was deposited in GenBank under the accession number PX705183. A BLASTn similarity search revealed that the sequence shared 99. 93% identity with that of the 16SrII-V subgroup reference strain ‘Candidatus Phytoplasma australasiaticum’ BAWM-TWN (GenBank accession no. GCA₀30586915. 1, 1, 383/1, 384 bp), and 99. 86% with the SPLL subgroup reference strain ‘Ca. P. australasiaticum subsp. Ipomoeae’ o7C (GenBank accession no. GCA₀24425275. 1, 1, 382/1, 384 bp) (Rodrigues Jardim et al. 2023). Moreover, Virtual RFLP analysis using iPhyClassifier (Zhao et al. 2009) revealed that the phytoplasma strain was a member of the 16SrII-A subgroup with a 1. 00 similarity coefficient to the reference phytoplasma strain (GenBank accession no. L33765). To validate the results, the translocase protein (secY) genes were amplified using primer pairs secYwbF1/secYwbR1 followed by secYwbF2/secYwbR2 (Wang et al. 2025), and the 0. 8-kb band was sequenced and deposited in GenBank (GenBank accession no. PX715155). BLAST analysis showed that the secY sequence of GDDPPE2502 shared 100% of sequence identities to several ‘Ca. P. australasiaticum’ strains (GenBank accession no. CP133702. 1, CP040925. 1, CP097312. 1 and CP171825. 1). To further characterize the phytoplasma, phylogenetic analysis based on the 16S rRNA and secY genes, conducted by MEGA 7. 0 (Kumar et al. 2016), confirmed that the GDDPPE2502 consistently clustered within the same subclade as the 16SrII group ‘Ca. P. australasiaticum’ related strain NCHU2014 (16SrII-A), BAWM-TWN (16SrII-V) and o7C (SPLL). Taken together, according to the latest ‘Candidatus Phytoplasma’ species description guidelines (Bertaccini et al. 2022; Rodrigues Jardim et al. 2023; Wei and Zhao 2022), the phytoplasma GDDPPE2502 was related to ‘Ca. P. australasiaticum’ (16SrII-A). To our knowledge, the present study is the first to report a ‘Ca. P. australasiaticum’ -related strain associated with yam bean in Guangdong, China. These findings highlight the need for further research to identify the potential insect vectors and transmission pathways, which will be beneficial for the epidemiological monitoring and prevention of the related diseases.
Sun et al. (Sun,) studied this question.