Publications

4535

ABSTRACT Crape jasmine is a beautiful evergreen flowering shrub and is native to India. During a survey in 2025, severe yellowing symptoms with stunted growth of the plant was observed on the crap jasmine plant at Bhopal, Central India. For the identification of ‘ Candidatus phytoplasma species’ on crap jasmine, symptomatic and asymptomatic leaf samples were collected and total DNA was extracted. The phytoplasma 16S rRNA gene was successfully amplified by direct and nested PCR using isolated DNA and phytoplasma‐specific primers from three symptomatic plants. The amplified ~1.2 kb nested PCR products from three samples were sequenced, and the resulting 16S rRNA gene nucleotide sequences were submitted to GenBank under the accession numbers PX442245, PX890108 and PX890109. Sequence analysis of all three isolates (PX442245, PX890108 and PX890109) revealed the highest nucleotide sequence identity (99%) and close phylogenetic relationships with reference strains of brinjal little leaf phytoplasma, ‘ Candidatus Phytoplasma trifolii’ (16SrVI group), predominantly belonging to the 16SrVI‐D subgroup. In silico RFLP analysis of the 16S rRNA gene sequences of the phytoplasma isolates under study showed the highest similarity to the reference strain of the 16SrVI‐D subgroup, with similarity coefficients ranging from 0.93 to 0.86. To the best of our knowledge, this is the first report of a ‘ Candidatus Phytoplasma trifolii’‐related strain (16SrVI‐D subgroup) associated with yellows disease of crape jasmine ( Tabernaemontana divaricata ) in India.

The endoplasmic reticulum (ER) stress response, or unfolded protein response (UPR), is crucial for cellular homeostasis and host defense. Its role in insect vectors of plant pathogens remains poorly understood. This study conducted a comprehensive molecular characterization of three core UPR genes—BiP, IRE1, and XBP1—in Diaphorina citri, the insect vector of the citrus huanglongbing pathogen Candidatus Liberibacter asiaticus (CLas). Expression profiling showed distinct developmental and tissue-specific patterns for these genes. The IRE1-mediated unconventional splicing of XBP1 mRNA was identified in D. citri and predicted across diverse insect pests. A semi-quantitative RT-PCR assay was established to detect this splicing event for monitoring ER stress. Time-course analysis of CLas-infected D. citri revealed an early activation (upregulation of BiP, IRE1, XBP1 transcripts, and increased XBP1 splicing) followed by later suppression of the UPR. Functional studies demonstrated that induction of ER stress with thapsigargin increased CLas titer. RNAi-mediated silencing showed that IRE1 silencing increased CLas proliferation, whereas XBP1 silencing reduced it. These findings provide foundational insights into the ER stress pathway in D. citri and demonstrate that the IRE1-XBP1 branch of the UPR plays a critical role in modulating CLas infection dynamics within its insect vector.

Abstract Citrus huanglongbing (HLB) associated with Candidatus Liberibacter spp. is the most destructive bacterial disease of citrus crops worldwide. In this study, the response of three-year-old seedlings of 14 commercial citrus cultivars and rootstocks to the Asian form of HLB disease ( Ca . L. asiaticus) was investigated through graft-inoculation. The seedlings' reactions to the HLB disease were evaluated based on the PCR detection of CLas after grafting, the disease incubation period (time between graft-inoculation and appearance of the first disease symptoms), and disease severity. Depending on the time of the positive PCR detection of CLas and appearance of disease symptoms, Mexican lime, Persian lime and Volkamer lemon were ranked at the highest level of tolerance (lowest susceptibility), and Rough lemon and Local orange were at the next level, i.e., semi-tolerance (intermediate susceptibility). Alemow, Bakraei, Rangpur lime, Cleopatra, Clementine mandarin, Local mandarin, Blood orange, and Washington navel orange were classified as susceptible to the disease, followed by Valencia orange, which was the most susceptible. In conclusion, all citrus genotypes studied, were affected by HLB. However, symptoms varied by cultivar, with the most severe observed on Valencia sweet orange and Local mandarin, while less severe symptoms were observed on Mexican lime, Persian lime and Volkamer lemon.