First Recorded Parasitism of Keteleeria evelyniana by Cuscuta chinensis in Yunnan, China.

Abstract

The genus Cuscuta, also known as dodder, comprising numerous holoparasitic plant species, exhibits a broad distribution across China, where it is recognized for its detrimental effects on indigenous florae (Narukawa, et al, 2021). Within this genus, Cuscuta chinensis stands out as a species of particular concern due to its potential to imperil a diverse array of plant species (Tang, et al, 2024). Notably, there is a dearth of literature documenting its parasitic interactions with K. evelyniana, a conifer species that is both ecologically and economically significant (Tang, et al, 2024). The ecological services provided by this species, along with the high quality of its timber, highlight its importance in both ecological and economic contexts. In our 2023 field expeditions, we documented for the first time the parasitic interaction between C. chinensis and K. evelyniana in Kunming, Yunnan Province, China (102°46'12″, 25°05'23″). The K. evelyniana plants parasitized by C. chinensis showed symptoms including chlorosis, wilting, and defoliation. The specimens collected presented yellow, leafless, twining stems with haustoria at the nodes, characteristic of C. chinensis. The species possess an umbel inflorescence containing 2 to 10 white flowers, each with a subtle pentamerous corolla. Morphological assessment identified the specimen as C. chinensis. We surveyed a 2.8-hectares area around an infected K. evelyniana, examining approximately 20 plants, and found only one instance of C. chinensis infection. Given its rarity and the presence of C. chinensis on other species outside this area, we consider K. evelyniana a rare host for this dodder. To ascertain the species identity with greater certainty, we sequenced the complete chloroplast genome using Illumina sequencing technology. Total genomic DNA was extracted from specimen stems and subjected to whole-genome sequencing. The chloroplast genome was subsequently assembled and annotated using the PGA (Plant Genome Annotation) tool (Qu et al. 2019), resulting in a complete chloroplast genome sequence that was deposited in GenBank (Accession number: PQ585822). The chloroplast genome has a length of 86,800 bp. BLAST analysis confirmed the species of the Dodder as C. chinensis, as it exhibited a 99.85% similarity with the previously uploaded sequence (Accession number MH780079), with 100% query coverage. Phylogenetic analyses (maximum likelihood with 1,000 bootstrap replicates and Bayesian inference with 2,000,000 MCMC generations, sampling every 1,000 generations) confirmed the specimen as C. chinensis. Ultimately, the specimen of the dodder recovered in Yunnan Province was classified as C. chinensis, employing a holistic approach that considered morphological attributes, sequence homology, and phylogenetic affiliations. A voucher specimen of K. evelyniana, parasitized by C. chinensis, is archived in the herbarium of the College of Horticulture and Landscape, Yunnan Agricultural University (No. 20230011). To our knowledge, this represents the first report of C. chinensis parasitizing K. evelyniana in China. This novel finding presents unprecedented conservation challenges for the preservation of K. evelyniana, while simultaneously enhancing our understanding of the host range and ecological significance of Cuscuta species.