Publications

4784

<p>Huanglongbing (HLB), caused by <em>Candidatus </em>Liberibacter asiaticus (CLas), continues to challenge citrus production in Saudi Arabia. Although HLB is widespread, there is still limited understanding of how temperature, season, host species, and the type of tissue sampled influence the reliability of CLas detection. In this regard, 123 CLas-positive samples sourced from major citrus-growing areas were analyzed. These samples included data from 4 major citrus species and 4 tissue types. Additionally, cycle threshold<strong> </strong>(Ct) values obtained through quantitative PCR for each sample were used to examine how climate and CLas interact in bacterial detection. As lower Ct values indicate higher bacterial abundance, an analysis of covariance (ANCOVA) was conducted to assess the influence of season, tissue type, citrus species, and average seasonal temperature on Ct values. The results demonstrated significant differences among tissue types, with petiole and midrib tissues exhibiting consistently lower Ct values. Additionally, lower Ct values were observed in spring and autumn, and higher Ct values in warmer summers and colder winters, based on average temperatures. Among the citrus species, only <em>Citrus limon</em> illustrated a prominent increase in CLas levels as temperatures increased. CLas levels in <em>C. limon</em> showed only minor fluctuations with temperature. Taken together, these results indicated that temperature gradients strongly shape CLas population levels in Saudi Arabia and influence the reliability of pathogen detection. Considering climatic context, along with tissue type and season can substantially improve sampling strategies and enhance the effectiveness of HLB monitoring programs in arid and semi-arid citrus production systems.</p>

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 coinfection 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 coinfection 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 coinfection 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 that APV1 infection likely represents an important risk factor for yellowing development in cultivated areca palm populations. These results confirm the coinfection of AYLP and APV1 on Hainan Island, offering epidemiological evidence for targeted disease management.

ABSTRACT Citrus Huanglongbing (HLB), caused by ‘ Candidatus Liberibacter asiaticus’ ( Ca Las), is the most devastating disease affecting the global citrus industry. Here, we reported that the Ca Las effector SDE70 promotes HLB pathogenicity by targeting the citrus ubiquitination pathway. Transgenic expression of SDE70 in Wanjincheng orange ( Citrus sinensis Osbeck) accelerated early Ca Las proliferation, aggravated HLB symptoms, and increased susceptibility to citrus canker induced by Xanthomonas citri subsp. citri ( Xcc ). These results demonstrate that SDE70 functions as a broad‐spectrum suppressor of citrus immunity. Mechanistically, SDE70 physically interacts with CsRUB2, a citrus ubiquitin‐related protein. Furthermore, CsRUB2 overexpression in Wanjincheng oranges reduced resistance to HLB but enhanced resistance to citrus canker. Both SDE70 and CsRUB2 elevated salicylic acid (SA) and hydrogen peroxide (H 2 O 2 ) levels in transgenic plants while lowering methyl salicylate (MeSA) levels. CsRUB2 also decreased jasmonic acid (JA). In contrast to the suppressive effect of SDE70, CsRUB2 enhanced the transcription of citrus immunity genes. Transient expression assays further demonstrated that the SDE70–CsRUB2 interaction dysregulates citrus immunity by perturbing SA, MeSA, JA, and H 2 O 2 signals. These findings provide a theoretical basis for understanding citrus– Ca Las interactions and breeding citrus varieties with broad‐spectrum resistance to both HLB and citrus canker.