First Report of Phelipanche aegyptiaca Parasitizing Cotyledon tomentosa in China

Cotyledon tomentosa Harv. (Crassulaceae), commonly known as bear's paw, is a popular succulent prized for its significant ornamental and economic value. In March 2024, however, a root holoparasite was discovered infecting approximately 25% of potted C. tomentosa plants in Shihezi, Xinjiang, China (86°03'36"E, 44°18'36"N). Morphological examination identified the parasite as Phelipanche aegyptiaca Pers. (Eizenberg et al. 2018). Each infected host plant supported 3 to 5 emerged shoots of P. aegyptiaca. The parasitic specimens were unequivocally assigned to P. aegyptiaca based on a suite of morphological characters: (i) erect, solitary stems 95-100 mm in height, slightly bulbous at the base and densely pubescent with glandular trichomes; (ii) inflorescence a lax, cylindrical, multiflowered raceme; (iii) bracts lanceolate, 6-8 mm long; (iv) calyx shortly campanulate, 7-8 mm long, with free, entire lobes; (v) corolla bilabiate, distinctly curved, 32 mm long, transitioning from a white base to a blue-purple apex; (vi) stamens 22 mm long, inserted 5-6 mm above the corolla base; (vii) pistil 10-15 mm long, comprising a glabrous ovary, a style adorned with short glandular hairs, and a bilobed stigma; and (viii) seeds ovoid to oblong, 0.3-0.4 mm in length, with a testa exhibiting prominent reticulate ornamentation, and a seed output ranging from 957 to 1204 per plant. For molecular characterization, genomic DNA was extracted from floral tissue. The internal transcribed spacer (ITS) region of ribosomal DNA was amplified with the primers ITS1/ITS4(Park et al. 2007). The resulting 670 bp amplicon was purified and sequenced (GenBank: PV362805). BLASTn analysis revealed that the sequence shared 96.38 % nucleotide identity with reference sequences of Phelipanche aegyptiaca (KC811171). Pathogenicity was verified through pot trials under controlled indoor conditions. Seeds of P. aegyptiaca were thoroughly incorporated into a growing medium (substrate:vermiculite, 2:1) at a density of 50 mg per kg of substrate. Five 8-week-old seedlings of C. tomentosa were transplanted into the infested substrate and three untreated control groups were included. All plants were maintained in a containment greenhouse at 25 ± 2°C under a natural photoperiod. The first signs of parasitism, including the formation of tubercles and haustorial connections, were observed within 102 days post-inoculation, followed by the emergence of aerial shoots. No symptoms developed on the control plants throughout the experiment. P. aegyptiaca is a devastating parasitic weed known to infest a wide range of hosts, including major crops in the Solanaceae and Fabaceae families (Yang et al. 2023), as well as certain ornamental species such as Kalanchoe blossfeldiana (Yousefi et al. 2014). In the present study, light infection did not induce conspicuous symptoms or damage on bear's paw plants; however, it did result in the completion of the parasite's life cycle. Furthermore, the soilborne infection detailed in this report was traced back to greenhouse soil that had been previously utilized for tomato cultivation and was contaminated with persistent seeds of P. aegyptiaca. This indicates that bear's paw can expedite the dissemination of P. aegyptiaca to regions previously free from its influence, and the parasitic weed may pose a severe threat to the production of bear's paw at high infection. To our knowledge, this is the first report of P.aegyptiaca parasitizing on C. tomentosa in China.