First report of Xanthomonas albilineans causing leaf scald on two chewing cane clones in Zhejiang province, China.

In recent years, outbreaks of leaf scald have been reported in two chewing cane clones "Guangdong Huangpi" and "Taoshang Guozhe" in Zhejiang province, China. From May to July 2019, we collected 11 and 13 leaf or stalk samples from symptomatic "Guangdong Huangpi" from four farms in Wenling and "Taoshang Guozhe" clones from three farms in Ruian, Zhejiang province, respectively. Leaves in young plants exhibited white pencil-line streaks (Supplement Fig. 1A & 1D) as well as partial or complete chlorosis of the leaf blade (Supplement Fig. 1B & 1E). Internal symptoms included an orange-red discoloration of the vascular bundles at the basal nodes of the stalk and discoloration extension into the internodes (Supplement Fig. 1C & 1F). Leaf and stalk tissues were used for bacterial isolation and purification on XAS medium, which is selective for Xanthomonas albilineans (Davis et al. 1994), using the streak plate method to obtain 24 isolates (Lin et al. 2018). Circular, convex, smooth, shiny and yellow colonies were isolated from all the samples. The pathogenicity of two isolates, XaCN30 from "Guangdong Huangpi" and XaCN43 from "Taoshang Guozhe", was confirmed with Koch's postulates according to the protocol reported by Lin et al. (2018). The incidences of diseased plants (56% and 63%) were observed in individual host clones at 28 d post-inoculation with isolates XaCN30 and XaCN43, respectively. Furthermore, all isolates were confirmed as X. albilineans via molecular methods. PCR amplification was conducted for all 24 isolates using the primer pairs XgyrB1F/XgyrB1R2 (Ntambo et al. 2019) and XAF1/XAR1 (Wang et al. 1999), which targeting the gyrB (encoding the b subunit of the DNA gyrase) and abc (encoding an ABC transporter) genes, and generating 904 bp and 608 bp amplicons, respectively. The PCR fragments were cloned into the pMD19-T vector (TaKaRa, Dalian, China). For each isolate, three single colonies of transformed Escherichia coli DH5α carrying targeted fragment were sequenced. These sequences were deposited into the GenBank with accession no. MT776053-MT776059 and MT776061-MT776077 for gyrB gene and MT776098-MT776104 and MT776106-MT776122 for abc gene. Based on the two concatenated DNA sequences of our 24 isolates, compared with 27 previously reported X. albilineans isolates obtained from the GenBank database, pairwise sequence identity analysis revealed that all 24 isolates from Zhejiang province had 99.4-100% identity with each other, 99.6-100% identity with 14 published domestic isolates, and 98.3-100% identity with 13 foreign isolates. Furthermore, phylogenetic analysis with MEGA 7.0 (Kumar et al. 2016) showed that the isolates from Zhejiang province clustered into two distinct groups (Supplement Fig. 2). One group consisted of 25 Chinese isolates (including all 11 isolates from Wenling) along with four isolates from the French West Indies (GPE PC73, GPE PC17, GPE PC86, and MTQ032), and one isolate from the USA (XaFL07-1), which were assigned to pulsed-field gel electrophoresis (PFGE) group B (Davis et al. 1997; Pieretti et al. 2012). A putative group was also proposed, which included all 13 isolates from Ruian, indicating that isolates from Ruian are distinct from the isolates isolated from other Chinese sugarcane-planting areas, including Wenling. We conclude that leaf scald disease in local clones of chewing cane are caused by X. albilineans in Zhejiang province in China, which will be helpful for leaf scald management in chewing cane, a cash crop.

Improved Primers for the Specific Detection of Leifsonia xyli subsp. xyli in Sugarcane Using a Conventional PCR Assay.

Ratoon stunting disease (RSD), one of the most important diseases of sugarcane, is caused by the bacterium Leifsonia xyli subsp. xyli (Lxx). Lxx infects sugarcane worldwide and RSD results in high yield losses and varietal degeneration. It is highly challenging to diagnose RSD based on visual symptomatology because this disease does not exhibit distinct external and internal symptoms. In this study, a novel Lxx-specific primer pair Lxx-F1/Lxx-R1 was designed to detect this pathogen using a conventional PCR assay. These primers were then compared with four published Lxx-specific primers and one universal Leifsonia generic primer pair LayF/LayR. Sugarcane leaf samples were collected from Saccharum spp. hybrids in commercial fields (315 samples) and from germplasm clones of five Saccharum species and Erianthus arundinaceus (216 samples). These samples were used for comparative field diagnosis with six conventional PCR assays. Sensitivity tests suggested that the PCR assay with primers Lxx-F1/Lxx-R1 had the same detection limit (1 pg of Lxx genomic DNA) as the primer pairs Cxx1/Cxx2 and CxxITSf#5/CxxITSr#5 and had 10-fold higher sensitivity than the primer pairs Pat1-F2/Pat1-R2, LayF/LayR, and C2F/C2R. Comparison of PCR assays revealed that natural Lxx-infection incidence (6.1%) in field sample evaluation identified by Lxx-F1/Lxx-R1 primers was higher than incidences (0.7 to 3.0%) determined by other primer pairs. Moreover, no nonspecific DNA amplification occurred within these field samples with Lxx-F1/Lxx-R1 primers, unlike with the primer pairs Cxx1/Cxx2 and LayF/LayR. Diverse Leifsonia strains were identified by PCR detection with LayF/LayR primers in the field samples, whereas whether these Leifsonia strains were pathogenic to sugarcane requires further research. Our investigations revealed that the PCR assay with the newly designed primers Lxx-F1/Lxx-R1 could be widely used for RSD diagnosis and Lxx-pathogen detection with satisfactory sensitivity and specificity.

Modulation of the properties of dinuclear lanthanide complexes through utilizing different ß-diketonate co-ligands: near-infrared luminescence and magnetization dynamics.

A family of new dinuclear lanthanide complexes as the simplest entities showing intramolecular magnetic interactions, [Ln2(dbm)2(L)2(CH3OH)2] (Ln = Tb (1), Dy (2), Ho (3), Er (4), Yb (5), Lu (6)), [Ln2(acac)2(L)2(EtOH)2] (Ln = Dy (7), Er (8)), [Dy2(TTA)2(L)2(CH3OH)2]·2CH2Cl2 (9) and [Dy2(tfa)2(L)2(CH3OH)2] (10) (H2L = N'-(2-hydroxy-5-methylphenyl)-pyrazine-2-carbohydrazide, Hdbm = 1,3-diphenyl-1,3-propanedione, Hacac = acetylacetone, HTTA = 2-thenoyltrifluoroacetone, Htfa = trifluoroacetylacetone), were constructed successfully by the reaction of a Schiff base ligand H2L and four different ß-diketonate salts. As for complexes 4, 5 and 8, all exhibit the characteristic emission peaks of the corresponding Er3+, Yb3+ and Er3+ ions, respectively. Meanwhile, the excitation wavelength (510 nm) of 5 is located in the visible region, confirming its significant potential application value. Magnetic studies indicate that complexes 9 and 10 exhibit characteristic slow relaxation of magnetization with the energy barriers (Ueff) of 102 K for 9 and 140 K for 10 under a zero dc field. Under the optimized dc fields, slow magnetic relaxations are present in 2 and 7, and the Ueff values of 9 and 10 have been improved. This proves that the ß-diketonate co-ligands deserve an important role in regulating Dy-SMMs influenced by the diverse perturbations of the axial crystal field originating from minor changes in the coordination environment.