Colletotrichum gloeosporioides and C. acutatum species complexes are causal agents of Colletotrichum leaf disease (CLD) of rubber trees worldwide. To determine the geographic distribution of Colletotrichum species complexes associated with CLD of rubber trees in Hainan, China, and their sensitivity to fungicides used in the region, a total of 275 Colletotrichum isolates were collected from 52 rubber tree plantations in 11 counties. These isolates were identified based jointly on morphological characteristics and PCR-based methodology. Of these isolates, 78 and 22% belonged to the C. gloeosporioides species complex (CGSC) and the C. acutatum complex (CASC), respectively. The incidence of CGSC isolates was greater than the CASC in all counties sampled. The incidence of CASC isolates appeared to be lower in the western and central south of Hainan than in other regions. There was no association in their presence at a given plantation between the two species complexes. The in vitro sensitivity of these two species complexes to carbendazim, chlorothalonil, and four demethylation inhibitor (DMI) fungicides (difenoconazole, propiconazole, myclobutanil, and prochloraz) was determined. Carbendazim was effective against CGSC but not against CASC with mean ED₅₀ values of 0.176 and 2.182 µg/ml, respectively. CASC isolates were more sensitive to difenoconazole, propiconazole, and myclobutanil (mean ED₅₀ values of 0.177, 0.129, and 1.424 µg/ml, respectively) than CGSC isolates (mean ED₅₀ values of 0.710, 0.348, and 3.496 µg/ml, respectively). Mean ED₅₀ values of CGSC against chlorothalonil and prochloraz were 173.341 and 0.035 µg/ml, respectively; corresponding values for CASC were 151.441 and 0.040 µg/ml. These results suggest that prochloraz, propiconazole, and difenoconazole are effective against both species complexes.

The cucurbit vegetable chieh-qua (Benincasa hispida var. chieh-qua How) is an important crop in South China and southeast Asian countries. Viral diseases cause substantial loss of chieh-qua yield. To identify the viruses that affect chieh-qua in China, ribosomal RNA-depleted total RNA sequencing was performed using chieh-qua leaf samples with typical viral symptoms. The virome of chieh-qua comprises four known viruses (melon yellow spot virus (MYSV), cucurbit chlorotic yellows virus (CCYV), papaya ringspot virus (PRSV) and watermelon silver mottle virus (WSMoV) and two novel viruses: cucurbit chlorotic virus (CuCV) in the genus Crinivirus and chieh-qua endornavirus (CqEV) in the genus Alphaendornavirus. The complete genomes of the two novel viruses in chieh-qua and three other isolates of CuCV in pumpkin, watermelon and cucumber were determined and the recombination signals of pumpkin and watermelon isolates of CuCV were detected. A reverse transcriptase PCR indicated that the dominant viruses of chieh-qua in Hainan are MYSV (66.67%) and CCYV (55.56%), followed by CuCV (27.41%), WSMoV (7.41%), cucumber mosaic virus (8.15%), zucchini yellow mosaic virus (6.67%), PRSV (6.67%) and CqEV (35.56%). Our findings support diagnostic and prevalence studies of viruses infecting chieh-qua in China, enabling sustainable control strategies for cucurbit viruses worldwide.

Root-knot nematodes (Meloidogyne spp.) are the most economically damaging group of plant-parasitic nematodes. They are considered to be a major constraint of pepper (Capsicum annuum L.) crops worldwide. In China, Hainan Island is the main producer of pepper, where the climatic conditions and cropping patterns are favorable for infection by Meloidogyne spp. In this study, we conducted a detailed investigation of the occurrence, severity, and population distribution of root-knot nematodes infesting pepper throughout Hainan Island. We also tested the level of resistance to M. enterolobii and M. incognita of the common pepper cultivars in Hainan. Our results showed that root-knot nematodes belonging to M. enterolobii, M. incognita, and M. javanica were found in Hainan, and the dominant population was M. enterolobii, which is the predominant species in the tropical area. Notably, all the pepper cultivars in this study were highly susceptible to M. enterolobii, which is probably a reason for its rapid spread throughout Hainan. The pepper cultivars exhibited different levels of resistance to M. incognita. This study promotes the comprehensive understanding of the root-knot nematode distribution and host resistance level of Meloidogyne in Hainan, which will guide the effective control of root-knot nematodes.

Viral diseases are one of the main categories of diseases that cause substantial yield losses in black pepper. Disease symptoms in black pepper are generally complex and are often caused by both known and undescribed viruses. To identify and clarify the etiology of viral diseases in black pepper in Hainan, China, we conducted high-throughput sequencing (HTS) by targeting purified double-stranded RNA (dsRNA) and ribosomal RNA depleted total RNA (rRNA-depleted totRNA). Analysis of the data revealed the presence of one known virus, piper yellow mottle virus (PYMoV), and three newly identified viruses: black pepper virus F (BPVF) in the genus Fabavirus, black pepper virus E (BPVE) in the genus Enamovirus, and black pepper virus B (BPVB) in the genus Badnavirus. The dominant viruses in P. nigrum sampled in Hainan are PYMoV, with an incidence of 100%, followed by BPVF (84%, 133 of 158) and BPVB (66%, 105 of 158). Mechanical inoculation of sap extracts from source plants containing PYMoV, BPVF, and BPVB gave negative results on both herbaceous and woody host plants 60 days postinoculation (dpi). BPVF and PYMoV were successfully transmitted to virus-free seedlings of black pepper through bark grafting, while BPVB was experimentally undetectable up to 150 dpi. Seed transmission experiments showed that no target viruses were present in all 59 germinated seedlings. This study provides information on diagnosis, prevalence, and transmission of black-pepper-associated viruses.