Publications

3867

Areca catechu palm is an important cash plant in Hainan Island of China and also in the tropical regions of the world. A. catechu palm yellow leaf (AcYL) disease caused by phytoplasmas is a devastating disease for plant production. In the study, the phytoplasmas associated with the AcYL disease were identified and characterized based on their conserved genes, and genetic variation and phylogenetic relationship of the phytoplasma strains in the 16SrXXXII group were demonstrated. The results indicated that A. catechu palm plants showing yellow leaf symptoms were infected by ‘Candidatus Phytoplasma malaysianum’-related strains belonging to the 16SrXXXII-D subgroup. BLAST and multiple sequence alignment analysis based on 16S rRNA and secA genes showed that the AcYL phytoplasmas shared 100% sequence identity and 100% homology with the ‘Ca. P. malaysianum’-related strains. Phylogenetic analysis indicated that the AcYL phytoplasmas and ‘Ca. P. malaysianum’-related strains belonging to the 16SrXXXII group clustered into one clade with a 100% bootstrap value. Based on computer-simulated digestions, six kinds of restriction fragment length polymorphism patterns within the 16SrXXXII group were obtained, and a novel subgroup in the 16Sr group was recommended to propose and describe the relevant strains in this 16Sr subgroup. To our knowledge, this is the first study to report that A. catechu palm showing yellow leaf symptoms was infected by ‘Ca. P. malaysianum’-related strains belonging to the 16SrXXXII group. A novel 16Sr subgroup, 16SrXXXII-F, was proposed based on the systematical analysis of genetic variation of all phytoplasmas within the 16SrXXXII group. The findings of this study will support references for monitoring the epidemiology and developing effective prevention strategies for AcYL disease.

A new disease syndrome of zucchini squash was observed in Southern Italy, in 2018 and again in 2020. Affected plants were severely stunted and leaves were bent downwards, small, stiff, thick, leathery, and had interveinal chloroses. In addition, flowers were virescent and fruits were deformed and often cracked. Disease incidence was 20 and 30% in two different zucchini cultivations in Campania region (Southern Italy). Tomato yellow leaf curl New Delhi virus (ToLCNDV) was detected in eight samples, by loop-mediated isothermal amplification–based (LAMP) kit and by PCR and Sanger sequencing of the AV1 gene. Phytoplasmas were detected in the same samples using nested PCR assays with primer pairs P1/P7 and R16F2n/R16R2. Phytoplasma associations in plant samples were confirmed using specific primers for the multilocus genes SecY, tuf and rp. Sequence comparison of multilocus genes and phylogenetic analyses of the 16S rDNA gene confirmed the association of a phytoplasma strain closely related to ‘Candidiatus Phytoplamsa asteris’. This is the first report of mixed infections of ToLCNDV and a putative ‘Ca. Phytoplamsa asteris’ strain in zucchini, associated with a new Squash-Phytoplasma-Begomovirus (SqPB) disease syndrome.

Two Gram-negative, aerobic, rod-shaped bacterial strains, 7MK25T and 6Y81T, were isolated from forest soil of Dinghushan Biosphere Reserve, Guangdong Province, PR China. Based on the results of 16S rRNA gene sequence analysis, strain 7MK25T showed the highest similarity (93.6 %) to Methyloferula stellata AR4T, followed by Bosea thiooxidans DSM 9653T (93.3 %). Strain 6Y81T had the highest similarity of 97.9 % to Lichenibacterium minor RmlP026T, followed by Lichenibacterium ramalinae RmlP001T (97.2 %). Phylogenomic analysis using the UBCG and PhyloPhlAn methods consistently showed that strain 7MK25T formed a sister clade to Boseaceae, while strain 6Y81T formed an independent clade within the genus Lichenibacterium, both in the order Hyphomicrobiales. The digital DNA–DNA hybridization and average nucleotide identity values between strains 7MK25T, 6Y81T and their close relatives were in the ranges of 19.1–29.9 % and 72.5–85.5 %, respectively. The major fatty acids of 7MK25T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C19 : 0 cyclo ω8c, C16 : 0 and C17 : 0 cyclo, while those of 6Y81T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), C16 : 0 and C16 : 0 3-OH. Strains 7MK25T and 6Y81T took diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine as their dominant polar lipids, and Q-10 as their major respiratory quinone. On the basis of phenotypic and phylogenetic data, strain 7MK25T is proposed to represent a novel species of a novel genus with name Terrirubrum flagellatum gen. nov., sp. nov., within a novel family Terrirubraceae fam. nov., with 7MK25T (=KCTC 62738T=GDMCC 1.1452T) as its type strain. Strain 6Y81T represents a novel species in the genus Lichenibacterium, for which the name Lichenibacterium dinghuense sp. nov. (type strain 6Y81T=KACC 21 727T=GDMCC 1.2176T) is proposed. Rhodoblastaceae fam. nov. with Rhodoblastus as the type genus is also proposed to solve the non-monophylectic problem of the family Roseiarcaceae.

Infections with phytoplasma present one of the most significant biotic stresses influencing plant health, growth, and production. The phytoplasma ‘Candidatus Phytoplasma solani’ infects a variety of plant species. This pathogen impacts the physiological and morphological characteristics of plants causing stunting, yellowing, leaf curling, and other symptoms that can lead to significant economic losses. The aim of this study was to determine biochemical changes in peony (Paeonia tenuifolia L.), mint (Mentha × piperita L.), and dill (Anethum graveolens L.) induced by ‘Ca. Phytoplasma solani’ in Serbia as well as to predict the impact of the biotic stress using artificial neural network (ANN) modeling. The phylogenetic position of the Serbian ‘Ca. Phytoplasma solani’ strains originated from the tested hosts using 16S rRNA (peony and carrot strains) and plsC (mint and dill strains) sequences indicated by their genetic homogeneity despite the host of origin. Biochemical parameters significantly differed in asymptomatic and symptomatic plants, except for total anthocyanidins contents in dill and the capacity of peony and mint extracts to neutralize superoxide anions and hydroxyl radicals, respectively. Principal Component Analysis (PCA) showed a correlation between different chemical parameters and revealed a clear separation among the samples. Based on the ANN performance, the optimal number of hidden neurons for the calculation of TS, RG, PAL, LP, NBT, •OH, TP, TT, Tflav, Tpro, Tant, DPPH, and Car was nine (using MLP 8-9-13), as it produced high r2 values (1.000 during the training period) and low SOS values. Developing an effective early warning system for the detection of plant diseases in different plant species is critical for improving crop yield and quality.

Abstract Huanglongbing (HLB), associated with the psyllid-vectored phloem-limited bacterium, Candidatus Liberibacter asiaticus (CLas), is a disease threat to all citrus production worldwide. Currently, there are no sustainable curative or prophylactic treatments available. In this study, we utilized mass spectrometry (MS)-based metabolomics in combination with 3D molecular mapping to visualize complex chemistries within plant tissues to explore how these chemistries change in vivo in HLB-impacted trees. We demonstrate how spatial information from molecular maps of branches and single leaves yields insight into the biology not accessible otherwise. In particular, we found evidence that flavonoid biosynthesis is disrupted in HLB-impacted trees, and an increase in the polyamine, feruloylputrescine, is highly correlated with an increase in disease severity. Based on mechanistic details revealed by these molecular maps, followed by metabolic modeling, we formulated and tested the hypothesis that CLas infection either directly or indirectly converts the precursor compound, ferulic acid, to feruloylputrescine to suppress the antimicrobial effects of ferulic acid and biosynthetically downstream flavonoids. Using in vitro bioassays, we demonstrated that ferulic acid and bioflavonoids are indeed highly bactericidal to CLas, with the activity on par with a reference antibiotic, oxytetracycline, recently approved for HLB management. We propose these compounds should be evaluated as therapeutics alternatives to the antibiotics for HLB treatment. Overall, the utilized 3D metabolic mapping approach provides a promising methodological framework to identify pathogen-specific inhibitory compounds in planta for potential prophylactic or therapeutic applications.