A Phytoplasma Related to ‘Candidatus Phytoplasma asteris’ Detected in Citrus Showing Huanglongbing (Yellow Shoot Disease) Symptoms in Guangdong, P. R. China

Abstract

Citrus huanglongbing (HLB) or yellow shoot disease (i.e., greening disease) is highly destructive to citrus production worldwide. Understanding the etiology of HLB is critical for managing the disease. HLB is currently associated with infection by 'Candidatus Liberibacter spp.' around the world, including China. However, Koch's postulates have not been fulfilled. In addition, other plant pathogens also may be involved in HLB. In a survey performed in Guangdong Province, P. R. China in 2006 and 2007, 141 citrus samples showing typical symptoms of HLB from 11 different cities were collected. Polymerase chain reaction (PCR) using phytoplasma-specific primer sets fU5/rU3 nested with primer set P1/P7 identified 110 (78.0%) positive samples. A 1,785-bp amplicon was obtained with primer set P1/P7. Analysis showed a 100% identity of this sequence in the region of 16S rDNA and 16S-23S rRNA intergenic transcribed spacer to three strains of 'Candidatus Phytoplasma asteri' (onion yellows [Japan], aster yellows 'watercress' [Hawaii], and valeriana yellows [Lithuania]). Of the 141 samples, 89 (63.1%) samples were positive for 'Ca. Liberibacter asiaticus'. When mixed infection was considered, 69 (48.9%) samples were positive for both 'Ca. P. asteri' and 'Ca. L. asiaticus'. Transmission electron microscopy (TEM) showed low titers of both walled and wall-less bodies in the phloem sieve tubes of HLB citrus. When transmission from symptomatic citrus to periwinkle (Catharanthus roseus) via dodder (Cuscuta campestris) was conducted, both phytoplasma and 'Ca. L. asiaticus' were detected from the affected periwinkle. In addition to yellowing/mottling, the infected periwinkle showed symptoms of virescence and phyllody which are commonly associated with phytoplasmal diseases. TEM analysis of affected periwinkle revealed pleomorphic and wall-less organisms, characteristic of phytoplasmas, filling some phloem sieve tubes. In contrast, walled bacteria were at low titer. This study showed that in addition to 'Ca. L. asiaticus', a phytoplasma related to 'Ca. P. asteri' could also be detected in citrus showing HLB symptoms in Guangdong.

Tuber transmission of ‘Candidatus Liberibacter solanacearum’ and its association with zebra chip on potato in New Zealand

“…In addition to Ca. L. asiaticus, a phytoplasma related to Candidatus Phytoplasma asteri was recently detected in Citrus showing HLB symptoms in Guangdong, P. R. China (Chen et al 2009). In New Zealand, Candidatus Phytoplasma australiense has been detected in potatoes showing zebra chip symptoms (Liefting et al 2009b).…”

Phytoplasmas and Phytoplasma Diseases: A Severe Threat to Agriculture

“…P. aurantifolia' includes Citrus aurantifolia, C. medica, C. limetta, C. lemon and C. jambhiri. Phytoplasmas belonging 16SrI and 16SrIX have been detected in a devastating citrus disease known as huanglongbing (HB) in Brazil mainly attributed to three species of Gram negative bacteria in the genus 'Candidatus Liberibacter', that is seriously threatening global citrus production [66] [67]. The pathogenic role of phytoplasmas was not clearly elucidated, but they can be detected in symptomatic plants in cases in which HB is not detected (R. Bassanezi, personal communication).…”

First report of ‘Candidatus Phytoplasma trifolii’ (16SrVI group) in Nagpur mandarin (Citrus reticulata) showing huanglongbing symptoms in central India

“…Although the disease is primarily attributed to 'Candidatus Liberibacter asiaticus', an unculturable α-proteobacterium, phytoplasmas belonging to the groups 16SrIX in Brazil (Texeira et al, 2008), 16SrII in China (Lou et al, 2014), and 16SrI in China (Chen et al, 2009) Liberibacter asiaticus' was tested by real-time PCR (ABI 7300, Applied Biosystems, USA) using specific16S rDNA-based TaqMan primer-probe sets (HLBasr/HLBp) (Li et al, 2006). To ascertain the association of phytoplasma, PCR was performed using P1/P7 universal primers specific to the 16S rRNA gene of phytoplasmas, followed by a nested PCR from a 1:30 dilution of the P1/P7 PCR products using primer sets R16F2n/R16R2 (Gundersen & Lee, 1996) and Fu5/Ru3 (Lou et al, 2014).…”