Agronomy and Crop Science

Grapevine yellows diseases occur in cultivated grapevine (Vitis vinifera L.) on several continents, where the diseases are known by different names depending upon the identities of the causal phytoplasmas. In this study, phytoplasma strains associated with grapevine yellows disease (North American grapevine yellows [NAGY]) in vineyards of Pennsylvania were characterized as belonging to 16S ribosomal RNA (rRNA) gene restriction fragment length polymorphism group 16SrI (aster yellows phytoplasma group), subgroup 16SrI-B (I-B), and variant subgroup I-B*. The strains (NAGYI strains) were subjected to genotyping based on analyses of 16S rRNA and secY genes, and to in silico three-dimensional modeling of the SecY protein. Although the NAGYI strains are closely related to aster yellows (AY) phytoplasma strains and are classified like AY strains in subgroup I-B or in variant subgroup I-B*, the results from genotyping and protein modeling may signal ongoing evolutionary divergence of NAGYI strains from related strains in subgroup 16SrI-B.

Abstract BACKGROUND In insects, little is known about the co‐evolution between their primary endosymbionts and hosts at the intraspecific level. This study examined co‐diversification between the notorious agricultural pest Diaphorina citri and its primary endosymbionts (P‐endosymbiont), ‘ Candidatus Carsonella ruddii’ at the population level. RESULTS Maximum likelihood, haplotype network, principal components and Bayesian clustering identified three lineages for D. citri and its P‐endosymbiont: a Western clade containing individuals from Pakistan, Bhutan (Phuentsholing), Vietnam (Son La), USA, Myanmar and China (Ruili, Yunnan); a Central clade, with accessions originating from Southwest China, Bhutan (Tsirang) and Bangladesh; and an Eastern clade containing individuals from Southeast Asia, and East and South China. A more diverse genetic structure was apparent in the host mitochondrial DNA than their P‐endosymbionts; however, the two sets of data were strongly congruent. CONCLUSION This study provides evidence for the co‐diversification of D. citri and its P‐endosymbiont during the migration from South Asia to East and Southeast Asia. We also suggest that the P‐endosymbiont may facilitate investigations into the genealogy and migration history of the host. The biogeography of D. citri and its P‐endosymbiont indicated that D. citri colonized and underwent a secondary dispersal from South Asia to East and Southeast Asia. © 2018 Society of Chemical Industry

AbstractHuanglongbing (HLB), also known as citrus greening, is a destructive disease of citrus; it is considered a newly emerging disease which has spread to the Middle East and North Africa (MENA). In Iran, the disease was first found in 2009. In this study, two hypervariable prophage and phage‐related loci, bacteriophage repressor protein C1 (CLIBASIA_ 01645 locus) and prophage terminase gene (CLIBASIA_05610 locus), were used to determine the diversity and characterization of Candidatus Liberibacter asiaticus (CLas) strains associated with HLB samples. Analyses of the CLIBASIA_01645 locus, characteristic of variable tandem repeat numbers (VTRNs), revealed the homogeneity of Iranian CLas isolates: However, this result showed two distinct genotypes (TRN < 10 and TRN > 10) of CLas in Iran. This is the first report documenting the presence of two differentially distributed genotypes of CLas in Iran. Sequence analysis of prophage terminase revealed the presence of two putative prophages (prophage I and prophage II) in the genome of CLas isolates of Iran. Frequency analysis of these two prophages by specific loci revealed the association between prophages populations, the development HLB symptoms and CLas genotypes and their interactions with another obligate symbiontic, HLB phytoplasma.

The Asian citrus psyllid (ACP) Diaphorina citri, vector of ‘Candidatus Liberibacter asiaticus’ (CLas), the putative causal agent of citrus Huanglongbing (HLB), is controlled by application of insecticides, which, although effective, has resulted in serious biological imbalances. New management tools are needed, and the technique known as “trap crop” has been attracting attention. A potential plant for use as a trap crop in the management of the ACP is Murraya koenigii (curry leaf). However, for this plant to be used in the field, it needs to be attractive for the vector and must not harbor CLas. To verify the potential of curry leaf as trap crop for the management of HLB, we investigated the ability of D. citri to transmit CLas to M. koenigii, and to other test plants, including M. paniculata (orange jasmine) and cultivar Valencia sweet-orange seedlings. For the tests, the insects were reared on a symptomatic CLas-infected plant and allowed to feed on the three test plant species. The overall maximum transmission rate for the citrus seedlings was 83.3%, and for orange jasmine was 33.3%. Successful transmission of CLas by ACP to the curry-leaf seedlings was not observed, and it was treated as immune to CLas. Supported by the previous results that M. koenigii is attractive for ACP, these results indicate that curry leaf is an excellent candidate for use as a trap crop, to improve the management of the insect vector and consequently of HLB.

‘Candidatus Liberibacter solanacearum’ (CLso) haplotype C is associated with disease in carrots and transmitted by the carrot psyllid Trioza apicalis. To identify possible other sources and vectors of this pathogen in Finland, samples were taken of wild plants within and near the carrot fields, the psyllids feeding on these plants, parsnips growing next to carrots, and carrot seeds. For analyzing the genotype of the CLso-positive samples, a multilocus sequence typing (MLST) scheme was developed. CLso haplotype C was detected in 11% of the T. anthrisci samples, in 35% of the Anthriscus sylvestris plants with discoloration, and in parsnips showing leaf discoloration. MLST revealed that the CLso in T. anthrisci and most A. sylvestris plants represent different strains than the bacteria found in T. apicalis and the cultivated plants. CLso haplotype D was detected in 2 of the 34 carrot seed lots tested, but was not detected in the plants grown from these seeds. Phylogenetic analysis by unweighted-pair group method with arithmetic means clustering suggested that haplotype D is more closely related to haplotype A than to C. A novel, sixth haplotype of CLso, most closely related to A and D, was found in the psyllid T. urticae and stinging nettle (Urtica dioica, Urticaceae), and named haplotype U.

AbstractOf late, the presence of Candidatus Phytoplasma trifolii was reported as a serious threat to the pepper crop in Zacatecas, México; therefore, asymptomatic and symptomatic pepper plants were collected from a commercial field among three samplings after the fruit set stage was reached. Total DNA was extracted using the CTAB‐based method and tested for phytoplasma using a nested PCR assay, followed by a BLAST, and restriction fragment length polymorphism (RFLP) analysis of 16S rDNA sequences, which confirmed the presence of phytoplasma group 16SrVI, “Candidatus Phytoplasma trifolii” in the symptomatic plants. As the metabolic pathways of pathogen‐infected plants tend to change, resulting in a biochemical differentiation with the noninfected plants, the polyphenolic compound concentrations were quantified from the vegetative tissues (root, stem, leaves and developed fruit/big bud) and were analysed based on a principal component analysis (PCA). Results revealed that, in general, plants tend to a progressive increase in total phenols, flavonoids, condensed tannins and anthocyanins related to the plants exposure to “Ca. P. trifolii” infection, and PCA demonstrated that almost 90% of the observed variance was explained by the first two components. Hence, the phenolic content of the plants increases as a response of the defence mechanism, which reflects its condition and resistance.