Horticulture

Pumpkin plants showing symptoms of witches’ broom (PuWB) were observed in Xinjiang Uyghur autonomous region, China, in September 2018. A phytoplasma was detected in symptomatic plants by PCR amplifying portions of the 16S ribosomal and tuf genes. In addition, the phylogeny based on these genes sequencing indicated that the PuWB strain clusters with ‘Candidatus Phytoplasma solani’ (subgroup 16SrXII-A). Furthermore, based on in silico and in vitro restriction fragment length polymorphism analyses, the PuWB phytoplasma was confirmed as a ‘Ca. P. solani’-related strain. This was the first record of the occurrence of phytoplasma presence in pumpkins in China, and the first record of 16SrXII phytoplasma infecting pumpkins in the world.

Abstract“Huanglongbing” (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from 183 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in three Caribbean countries (Cuba, Jamaica, and Guadeloupe-France), were collected to verify the possible co-infection of ‘Candidatus Phytoplasma’ and ‘Candidatus Liberibacter’ species. The 64% of the samples resulted positive to the ‘Ca. L. asiaticus’ and the 27% to diverse ‘Ca. Phytoplasma’-related species, moreover about the 14% of the samples infected with ‘Ca. Liberibacter’ were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Moreover the detection of only phytoplasmas in 11 symptomatic citrus samples collected from Cuba and Guadeloupe without ‘Ca. Liberibacter’ detection, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular detection is necessary to identify single or mixed infections. Diaphorina citri insects collected from Cuba and Guadeloupe resulted infected with ‘Ca. L. asiaticus’ confirming its active role in the dissemination of the pathogen. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Considering that the phytoplasmas belonging to some ‘Candidatus species’ were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attribute to citrus orchards.

Abstract Whole‐genome sequencing of “ Candidatus Liberibacter asiaticus” (Las) indicated some polymorphic gene regions enabling the molecular characterization of this bacterium. Although the population diversity of Las in China has been previously studied, no reports have used a combination of a prophage region and short tandem repeat (STR) loci for phylogenetic relationship characterization. In this study, we investigated the genetic diversity and structure of 667 Las strains from nine provinces in southern China using multiple genetic loci including three type‐specific prophage loci, two STR loci, and a miniature inverted‐repeat transposable element (MITE) region. The results indicated that the genetic diversity varied according to the gene loci used. The prophage regions, including the MITEs, revealed significant genetic differences of Las populations in Yunnan and Guizhou from other provinces, while the STR loci only indicated a difference of Las population in Guizhou from those of other provinces. In particular, the Las population shown to be diverse in Jiangxi at the CLIBASIA_01215_STR locus was not diverse when measured using the other loci. Considering all loci, the Las populations from Yunnan and Guizhou were different, those from Guangdong and Guangxi were complex, while the Las population in Jiangxi was comparatively simple. Las populations from five neighbouring provinces, including Guangdong, Guangxi, Hunan, Fujian, and Jiangxi were grouped in a big cluster. The Las population structure changed with age according to the prophage type. This study evaluated the method used for studying the molecular diversity of Las populations and provided more detailed information on the geographical origin and epidemic trend of Chinese Las populations.

AbstractCitrus Greening disease (CG) in South Africa (SA) is associated with the fastidious bacterium ‘CandidatusLiberibacter africanus’ (Laf). It has been observed that Laf isolates obtained from different geographic localities in SA differed in the rate of transmission during grafting experiments leading to the hypothesis that genetic variation of Laf may exist in this country. To determine this, 167 Laf isolates obtained from Limpopo, North West, Mpumalanga and the Western Cape were subjected to microsatellite analyses, using four polymorphic markers. From UPGMA and STRUCTURE analysis, it was shown that most sources belong to one of two major genetic groups of Laf and these comprise 25 distinct haplotypes. Four samples included within this study did not group with these two major groups, suggesting a potential third and fourth genetic group of Laf being present, which can be validated by further sampling. Results further indicate that Laf populations in SA are formed by geographic locality. The high genetic diversity observed for Laf within this study is consistent with the hypothesis that Laf originated on the African continent, warranting further genetic analysis of Laf populations from Africa. This is the first study to unveil the genetic diversity of Laf.

iaphorina citri is considered the most dangerous citrus pest because it transmits Candidatus Liberibacter asiaticus, the causal agent of Huanglongbing (HLB). Like other hemiptera insects, D. citri has developed mutualistic interactions with prokaryotic organisms known as endosymbionts. This symbiosis can be obligatory, when the interaction occurs with a primary endosymbiont, or facultative, when it is a secondary endosymbiont. Symbiosis is essential for various physiological functions, but some endosymbionts can adversely affect the psyllid's abilities. D. citri is associated with a great diversity of endosymbionts, with Candidatus Carsonella ruddii, Candidatus Profftella armatura, Candidatus Wolbachia spp. and Candidatus Liberibacter spp standing out. The aim o symbiotic relationship, prokaryotes, Candidatus Wolbachia, transmission of Candidatus Liberibacter asiaticus.