Influence of temperature on infection and establishment of ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ in citrus plants

Abstract

The objectives of this work were (i) to determine the influence of temperature on infection of citrus by 'Candidatus Liberibacter asiaticus' and 'Candidatus Liberibacter americanus', the two bacterial species associated with citrus huanglongbing (HLB) in Brazil, and (ii) to determine the influence of temperature on citrus colonization by 'Ca. L. asiaticus', which has taken over from 'Ca. L. americanus' as the predominant species in Brazil since 2008. Two experiments were carried out with graft-inoculated Valencia oranges on Rangpur lime rootstocks. Immediately after inoculation the plants were maintained for 423 days in growth chambers under the following night ⁄ day temperature conditions: 17 ⁄ 22, 22 ⁄ 27 or 27 ⁄ 32°C, with a dark ⁄ light photoperiod of 8 ⁄ 16 h. Infection and colonization of plants were determined using quantitative PCR (qPCR). 'Candidatus Liberibacter americanus' did not infect the plants maintained at 27 ⁄ 32°C; however, infection by 'Ca. L. asiaticus' occurred at all studied temperatures. Two months after inoculation, 'Ca. L. asiaticus' was distributed throughout the inoculated plants, with mean C t values in the range of 30-31 for leaves and 25-28 for roots. Over time, 'Ca. L. asiaticus' reached the highest titres in mature leaves (mean C t value = 26AE7) of citrus plants maintained at 22 ⁄ 27°C. 'Candidatus Liberibacter asiaticus' colonization of citrus plants was negatively affected by the daily temperature regime of 27 ⁄ 32°C (mean C t value in mature leaves = 33AE6).

Incidence of “Candidatus Liberibacter asiaticus” in a Florida population of Asian citrus psyllid

“…L. asiaticus” can infect and spread within a plant at daytime temperatures continually as high as 32°C, but population levels of “ Ca . L. asiaticus” in citrus were lower in plants held at a continual daytime temperature of 32°C than of 27°C (Gasparoto et al., ). “ Ca .…”

Draft Genome Sequence of “ Candidatus Liberibacter americanus” Bacterium Associated with Citrus Huanglongbing in Brazil

“…Liberibacter americanus” and the high titer in “ Ca . Liberibacter asiaticus”-infected symptomatic plants might account for a competitive advantage of the latter during the natural transmission by psyllids (6, 7). Hitherto, “ Ca .…”

Quantitative Distribution of Candidatus Liberibacter asiaticus in the Aerial Parts of the Huanglongbing-infected Citrus Trees in Texas

“…They concluded that CLas infection is systemic or nearly completely systemic in the trees; however, the bacterial concentrations in different portions of the tree may be below detectible levels. Furthermore, a recent study showed that temperature influences infection and establishment of CLas and CLam in citrus plants where the highest CLas titers were observed in citrus plants maintained at 22/27°C and CLas concentrations were negatively affected by a daily temperature regime of 27/32°C (Gasparoto et al, 2012). Additionally, it was reported that continuous exposure to 40 to 42°C for a minimum of 48 h significantly reduced CLas titers or even eliminated CLas from infected citrus seedling (Hoffman et al, 2013).…”