Genome analysis of Spiroplasma citri strains from different host plants and its leafhopper vectors.

BACKGROUND: Spiroplasma citri comprises a bacterial complex that cause diseases in citrus, horseradish, carrot, sesame, and also infects a wide array of ornamental and weed species. S. citri is transmitted in a persistent propagative manner by the beet leafhopper, Neoaliturus tenellus in North America and Circulifer haematoceps in the Mediterranean region. Leafhopper transmission and the pathogen's wide host range serve as drivers of genetic diversity. This diversity was examined in silico by comparing the genome sequences of seven S. citri strains from the United States (BR12, CC-2, C5, C189, LB 319, BLH-13, and BLH-MB) collected from different hosts and times with other publicly available spiroplasmas. RESULTS: Phylogenetic analysis using 16S rRNA sequences from 39 spiroplasmas obtained from NCBI database showed that S. citri strains, along with S. kunkelii and S. phoeniceum, two other plant pathogenic spiroplasmas, formed a monophyletic group. To refine genetic relationships among S. citri strains, phylogenetic analyses with 863 core orthologous sequences were performed. Strains that clustered together were: CC-2 and C5; C189 and R8-A2; BR12, BLH-MB, BLH-13 and LB 319. Strain GII3-3X remained in a separate branch. Sequence rearrangements were observed among S. citri strains, predominantly in the center of the chromosome. One to nine plasmids were identified in the seven S. citri strains analyzed in this study. Plasmids were most abundant in strains isolated from the beet leafhopper, followed by strains from carrot, Chinese cabbage, horseradish, and citrus, respectively. All these S. citri strains contained one plasmid with high similarity to plasmid pSci6 from S. citri strain GII3-3X which is known to confer insect transmissibility. Additionally, 17 to 25 prophage-like elements were identified in these genomes, which may promote rearrangements and contribute to repetitive regions. CONCLUSIONS: The genome of seven S. citri strains were found to contain a single circularized chromosome, ranging from 1.58 Mbp to 1.74 Mbp and 1597-2232 protein-coding genes. These strains possessed a plasmid similar to pSci6 from the GII3-3X strain associated with leafhopper transmission. Prophage sequences found in the S. citri genomes may contribute to the extension of its host range. These findings increase our understanding of S. citri genetic diversity.

Identification of QTLs controlling resistance to Pseudomonas syringae pv. tomato race 1 strains from the wild tomato, Solanum habrochaites LA1777.

KEY MESSAGE: Screening of wild tomato accessions revealed a source of resistance to Pseudomonas syringe pv. tomato race 1 from Solanum habrochaites and facilitated mapping of QTLs controlling disease resistance. Pseudomonas syringae pv. tomato (Pst) causes bacterial speck of tomato, which is one of the most persistent bacterial diseases in tomato worldwide. Existing Pst populations have overcome genetic resistance mediated by the tomato genes Pto and Prf. The objective of this study was to identify sources of resistance to race 1 strains and map quantitative trait loci (QTLs) controlling resistance in the wild tomato Solanum habrochaites LA1777. Pst strains A9 and 407 are closely related to current field strains and genome sequencing revealed the lack of the avrPto effector as well as select mutations in the avrPtoB effector, which are recognized by Pto and Prf. Strains A9 and 407 were used to screen 278 tomato accessions, identifying five exhibiting resistance: S. peruvianum LA3799, S. peruvianum var. dentatum PI128655, S. chilense LA2765, S. habrochaites LA2869, and S. habrochaites LA1777. An existing set of 93 introgression lines developed from S. habrochaites LA1777 was screened for resistance to strain A9 in a replicated greenhouse trial. Four QTLs were identified using composite interval mapping and mapped to different chromosomes. bsRr1-1 was located on chromosome 1, bsRr1-2 on chromosome 2, and bsRr1-12a and bsRr1-12b on chromosome 12. The QTLs detected explained 10.5-12.5% of the phenotypic variation. Promising lines were also subjected to bacterial growth curves to verify resistance and were analyzed for general horticultural attributes under greenhouse conditions. These findings will provide useful information for future high-resolution mapping of each QTL and integration into marker-assisted breeding programs.

Distribution and persistence of tricyaclazole in agricultural field soils.

Soil is the major sink for majority of pesticides applied on agricultural crops and its fate depends on variety of factors. There is little research on fate of pesticide in field soil under different climatic conditions and there is a need of study on the influence of climate on pesticide degradation and persistence in soil. In the present study, the persistence and distribution of tricyclazole was investigated in rice field soil under the influence of cold winter condition. Field experiment was carried at 35 different field sites from 6 provinces in Republic of Korea. Limit of detection and limit of quantification of tricyclazole were found to be 0.005 and 0.0165 mg/kg, respectively. The concentrations of tricyclazole in soil samples ranged from 0.387 mg/kg in sites in Gyeongsangbuk-do areas and lowest 0.021 mg/kg in sites from Chuncheongnam-do areas. In natural environmental conditions, tricyclazole persisted longer than 11 months post application in agricultural field soils. Our result indicates the influence of cold climatic condition on the persistence of tricyclazole.

Complete genome sequence of Japanese erwinia strain ejp617, a bacterial shoot blight pathogen of pear.

The Japanese Erwinia strain Ejp617 is a plant pathogen that causes bacterial shoot blight of pear in Japan. Here, we report the complete genome sequence of strain Ejp617 isolated from Nashi pears in Japan to provide further valuable insight among related Erwinia species.