Publications

4364

Areca palm yellow leaf phytoplasma (AYLP) and Areca palm velarivirus 1 (APV1) are two critical pathogens associated with yellow leaf in areca palm, resulting in devastating damage to areca production. However, evidence of their co-infection remains unclear. Areca palms showing yellow leaf symptoms (suspected to be caused by phytoplasma and velarivirus 1) were surveyed and sampled around Hainan Island of China and the pathogens were identified and analyzed in the study. The results showed that infectious leaf yellowing symptoms of areca palms primarily occurred in eastern and southern cities and counties of Hainan Island. Molecular identification revealed co-infection of 'Candidatus Phytoplasma asteris' (16SrI-B subgroup) and APV1 in individual areca palm samples. Among 520 samples tested by qPCR, AYLP was detected in 23.46% (n=122), APV1 in 53.46% (n=278), and a co-infection with both AYLP and APV1 in 10.96% (n=57). A statistically significant difference in APV1 detection rate was observed between asymptomatic and symptomatic plantations (P < 0.0001), suggesting APV1 infection likely represents an important risk factor for yellowing development in cultivated areca palm populations. These results confirm the co-infection of AYLP and APV1 on Hainan Island, offering epidemiological evidence for targeted disease management.

ABSTRACT The stolbur disease associated with “ Candidatus Phytoplasma solani” (CaPsol) is very common in Europe and the Mediterranean regions and adversely affects perennial or annual plants but is rarely reported on cucurbits. We report the first multilocus genetic characterisation of CaPsol strains infecting cucurbit plants and the presence of some RNA viruses prevalent in cucurbits. Between 2019 and 2020, 156 symptomatic and nine asymptomatic plant samples were collected during surveys in cucurbit‐growing areas. Symptomatic plants exhibited leaf deformation, growth retardation, yellowing, flower deformation and other virus‐like symptoms. Molecular testing detected potyviruses, tobamoviruses and Cucumis melo endornavirus (CmEV) as single and double infections in 108 samples, but CaPsol was determined only in seven plants as a single infection. CaPsol strains infecting squash and watermelon in the Marmara region of Türkiye were genetically characterised by describing their tuf, vmp1 and stamp gene sequences. All cucurbit‐associated CaPsol strains were of the tuf ‐b1 genotype and five different stamp genotypes previously reported in other crops and wild plant reservoirs in Europe. Cucurbit CaPsol strains had vmp1 gene sequences corresponding to RFLP types V4 and V14, previously detected in the Mediterranean basin. These strains were not novel cucurbit‐specific genotypes but shared similarities with genotypes from diverse plant hosts across Europe. This indicated that CaPsol is not restricted to cucurbits and may persist in alternative plant hosts. Thus, disease management should include monitoring alternative plant reservoirs, rather than focusing solely on cucurbit production areas. Viral infections showed significantly higher prevalence compared to phytoplasma infections in the region.

Abstract Citrus Huanglongbing (HLB) is one of the most devastating diseases in the citrus industry and is caused primarily by ‘Candidatus Liberibacter asiaticus’ (CLas), a phloem-restricted gram-negative bacterium transmitted via citrus psyllids in the field. Precise CLas detection is crucial for HLB control, particularly during extensive surveys in new emerging regions. Unfortunately, the lack of a practical on-site detection method for CLas due to the limited specificity of immunostrips and the costive non-user friendliness approaches prevent the effective disease control. In this study, a probe-based recombinase polymerase amplification (RPA) targeting the CLas five-copy nrdB gene (β-subunit of ribonucleotide reductase, RNR) was developed and evaluated for its specificity, sensitivity, and reliability. To enhance user-friendliness and facilitate widely use, an All-in-one kit was premade as freeze-dried pellets in individual tubes, containing all necessary components except DNA template. The applicability of the All-in-one kit for CLas detection was confirmed using plant or psyllid crude DNA extracts. Collectively, the All-in-one kit offers a specific, sensitive, rapid, cost-effective, and practical alternative for diagnosing CLas in field conditions when coupled with simplified crude DNA extraction method, providing an alternative approach for on-site CLas detection in the context of HLB.