Obscure morning glory (Ipomoea obscura) is a perennial vine with attractive flowers in the family of Convolvulaceae. In China, this plant is widely distributed throughout the tropical and subtropic...

Coconut lethal yellowing (LY) diseases caused by phytoplasmas are devastating diseases for coconut cultivation, seriously threating the coconut industry around world. The phytoplasmas associated with the LY diseases belonged to 6 16Sr groups containing 16SrI, 16SrIV, 16SrXI, 16SrXIV, 16SrXXII and 16SrXXXII, with comparatively higher variable level. Conserved regions of the 16S rRNA genes of LY phytoplasmas belonging to the 6 16Sr groups were obtained in the study. Based on the conserved region sequences of 16S rRNA genes, 2 sets of LAMP primers, Co-4 and Co-6, were designed and screened, and the rapid and visual detection methods universal for different groups LY phytoplasmas were established. The entire detection reactions of the universal detection methods could be completed by only 30-40 minutes of constant temperature amplification at 64 °C, and the detection results were judged by the color changes of the reaction systems, which are convenient and quick. For the 6 groups phytoplasmas, the estimated minimum detection limit range of the universal detection primers Co-4 and Co-6 were identical, 4.8×101- 4.8×107 copies per 200 μL. The universal detection methods for the LY phytoplasmas established in the study are of great significance for the rapid diagnosis and identification, the efficient monitoring and early warning as well as the port inspection and quarantine of the LY phytoplasmas and their related diseases.

Vernonia cinerea (L.)Less. is an annual herbaceous plant of the Asteraceae family, which is widely distributed throughout Southeast Asia, India, and the tropical and subtropical regions of China. This herb is known to contain various bioactive compounds and is commonly used in traditional system of medicine in China and India (Singh et al. 2021). During the spring of 2022 and 2023, powdery mildew symptoms were observed on 70% of V. cinerea plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 104 to 188 × 11 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 32 to 57 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 19 to 45 ×16 to 26 m (length/width ratio = 1.2 to 2.4), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMVC-22. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 577-bp sequence was deposited in GenBank (accession no. OP765400). A BLASTn search in GenBank of this sequence showed 100% similarity with the ITS sequences of P. xanthii isolates from China (MT260063, MT739423 and MT131253), Thailand (LC270780), and Vietnam (KM260731). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OP765401). This region shared 100% similarity with P. xanthii isolates (LC371333, LC270780, and AB936277) as well. Powdery mildew from Hainan sample belonged to the P. xanthii group with strong bootstrap values support 99% in maximum likelihood phylogenetic tree based on ITS and 28S gene sequences. To confirm pathogenicity, five healthy potted plants of V. cinerea were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. In different countries and regions, Erysiphe cichoracearum has been previously reported on some Vernonia species, including V. Galamensis from southern parts of Ethiopia (Hundesa and Mekonnen 2017). To our knowledge, this is the first record of P. xanthii infecting V. cinerea in China. We are concerned that the pathogen could become a threat to the widespread planting of V. cinerea in the future.

Chamber bitter (Phyllanthus urinaria L.), a species of the Euphorbiaceae family, is an annual perennial herbal species distributed in tropical Asia, America, China and the Indian Ocean islands. In ...

The forage legume phasey bean Macroptilium lathyroides (L.) Urb. is an annual or short-lived perennial of the family Fabaceae. It is native to the tropical and subtropical areas from North to South America, and is naturalized throughout the tropics and subtropics of the world (Tobisa and Nakano 2019). It is mainly used for forage, green manure, and slope protection (Silva et al. 2018). In addition, the nitrogen fixation ability of this plant can also improve the soil. In February 2022 and January 2023, powdery mildew symptoms were observed on 70% of M. lathyroides plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 100 to 233 × 8 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 36 to 56 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 24 to 34 ×13 to 20 m (length/width ratio = 1.5 to 2.3), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMML-23. To confirm the identification, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 575-bp sequence was deposited in GenBank (accession no. OR240256). A BLASTn search in GenBank of this sequence showed 100% similarity with the ITS sequences of P. xanthii isolates from China (MT242593, MK439611 and MH143483), Korea (MG754404), Vietnam (KM260704), Japan (MZ604267), and Puerto Rico (OP882310). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OR240255). This region shared 100% similarity with P. xanthii isolates (MK357436, LC371333, OP765401, and MZ604267) as well. To confirm pathogenicity, five healthy potted plants of M. lathyroides were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. This fungus has been reported causing powdery mildew on M. atropurpureum in Thailand (Meeboon et al. 2016). In the United States phasey bean powdery mildew caused by Erysiphe fallax has been previously reported (Poudel and Zhang 2019). To our knowledge, this is the first record of P. xanthii infecting M. lathyroides in China. Over the past 50 years of introduction, phasey bean has become one of the main leguminous forages for establishing artificial mixed seeding grasslands in southern China. We are concerned that the pathogen could become a threat to the widespread planting of M. lathyroides in the future.

Ixeris denticulata (Houtt.) Stebb is an annual herbaceous plant in the family of Asteraceae, which is native to Europe or central Asia. This plant is widely distributed in China and is commonly use...