scholarly journals Canopy health, but not Candidatus Liberibacter asiaticus Ct values, are correlated with fruit yield in Huanglongbing affected sweet orange trees

2021 ◽  
Author(s):  
Amit Levy ◽  
Taylor Livingston ◽  
Chunxia Wang ◽  
Diann Achor ◽  
Tripti Vashisth
Keyword(s):  
Sweet Orange ◽  
Field Trials ◽  
Fruit Yield ◽  
Ct Value ◽  
Independent Field ◽  
Canopy Volume ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Almost All ◽  
Orange Trees

AbstractIn Florida, almost all citrus trees are infected with Huanglongbing (HLB), caused by the gram-negative, intracellular phloem limited bacteria Candidatus liberibacter asiaticus (CLas). Distinguishing between the severely and mildly sick trees is important for managing the groves and testing new HLB therapies. A mildly sick tree is one that produces higher fruit yield, compared to a severely sick tree, but measuring yields is laborious and time consuming. Here we characterized HLB affected sweet orange trees in the field in order to identify the specific traits that are correlated with the yields. We found that canopy volume, fruit detachment force (FDF) and the percentage of photosynthetically active radiation interception in the canopy (%INT) were positively correlated with fruit yields. Specifically, %INT measurements accurately distinguished between mild and severe trees in independent field trials. We could not find a difference in the Ct value between high and low producing HLB trees. Moreover, Ct values did not always agree with the number of CLas in the phloem that were visualized by transmission electron microscopy. Overall, our work identified an efficient way to distinguish between severe and mild HLB trees in Florida by measuring %INT and suggests that health of the canopy is more important for yields than the Ct value.

scholarly journals Ultrastructural Changes and Putative Phage Particles Observed in Sweet Orange Leaves Infected with ‘Candidatus Liberibacter asiaticus’

Plant Disease ◽  
2015 ◽  
Vol 99 (3) ◽  
pp. 320-324 ◽  
Author(s):  
S. M. Fu ◽  
John Hartung ◽  
C. Y. Zhou ◽  
H. N. Su ◽  
J. Tan ◽  
...  
Keyword(s):  
Sweet Orange ◽  
Light And Electron Microscopy ◽  
Ultrastructural Changes ◽  
Candidatus Liberibacter Asiaticus ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Orange Trees ◽  
First Time ◽  
Citrus Disease ◽  
Putative Phage

Huanglongbing (HLB), also known as citrus greening, is currently the most destructive citrus disease. Anatomical analyses of HLB-affected sweet orange were carried out by light and electron microscopy. As compared with healthy citrus, the phloem plasmodesmata were plugged with callose, and in some samples the phloem was collapsed. Chloroplast structures were deformed. Prophage sequences occupy a significant portion of the genome of ‘Candidatus Liberibacter asiaticus’ and have been used to distinguish strains from Yunnan and Guangdong provinces in China and Florida. Interestingly, a large number of possible putative phage particles were observed attached on the surface of ‘Ca. L. asiaticus’ cells in plants inoculated with strain FJ3 from Fujian Province, China. Phage particles have been observed previously only in periwinkle plants artificially inoculated in Florida with ‘Ca. L. asiaticus’ that carried the SC1-type prophage. PCR assays verified the presence of the SC1-type prophage sequences previously described from this bacterium in Florida in the FJ3 isolate. This is the first time that suspected phage particles have been observed in sweet orange trees infected with ‘Ca. L. asiaticus.’

scholarly journals Different Sweet Orange‒Rootstock Combinations Infected by Candidatus Liberibacter asiaticus under Greenhouse Conditions: Effects on the Roots

HortScience ◽  
2022 ◽  
Vol 57 (1) ◽  
pp. 56-64
Author(s):  
Shahrzad Bodaghi ◽  
Gabriel Pugina ◽  
Bo Meyering ◽  
Kim D. Bowman ◽  
Ute Albrecht
Keyword(s):  
Root Growth ◽  
Imaging System ◽  
Sweet Orange ◽  
Field Performance ◽  
Field Trials ◽  
Relative Distribution ◽  
Production Environment ◽  
Citrus Diseases ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus

Grafting a scion onto a rootstock results in physical and physiological changes in plant growth and development, which can affect tree vigor, productivity, and tolerance to stress and disease. Huanglongbing (HLB) is one of the most destructive citrus diseases and has become endemic in Florida since its introduction in 2005. It is associated with the phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas), which cause severe metabolic disruptions in affected plants. Although most scion cultivars are highly susceptible, some rootstock cultivars are tolerant and allow the grafted tree to cope better with the disease. The objectives of this study were to identify rootstock traits that can be used to assess cultivars under controlled greenhouse conditions in advance of longer-term field trials. We used 10 commercially important rootstocks with different genetic backgrounds and known field performance in graft combination with ‘Valencia’ sweet orange scion. Trees were graft-inoculated with CLas and compared against mock-inoculated trees. Tree health and CLas populations were assessed regularly, and root growth was monitored using a minirhizotron imaging system. Plants were excavated and destructively sampled 21 months after inoculation to assess biomass distributions and other CLas-induced effects. We found significant differences between healthy and infected trees for most variables measured, regardless of the rootstock. In contrast to leaf CLas titers, root titers were significantly influenced by the rootstock, and highest levels were measured for ‘Ridge’ sweet orange and sour orange. Root growth and root biomasses were reduced upon infection but differences among rootstocks did not always agree with reported field performances. Despite severe biomass reductions plants maintained their relative distribution of biomass among different components of the root system, and no dead roots were observed. Root respiration was reduced by CLas infection and was overall higher in tolerant cultivars suggesting its potential as a physiological marker. This study improves our knowledge about the strengths and weaknesses of assessing rootstock traits of grafted trees in a controlled greenhouse setting. Results from the study suggest that in addition to HLB tolerance, other rootstock traits will ultimately have major contributions to field survival and productivity of the grafted trees in an HLB endemic production environment.

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

HortScience ◽  
2014 ◽  
Vol 49 (1) ◽  
pp. 65-68 ◽  
Author(s):  
Madhurababu Kunta ◽  
John V. da Graça ◽  
Nasir S.A. Malik ◽  
Eliezer S. Louzada ◽  
Mamoudou Sétamou
Keyword(s):  
Sweet Orange ◽  
Plant Parts ◽  
Citrus Greening Disease ◽  
Bacterial Titer ◽  
Citrus Groves ◽  
Significant Difference ◽  
Bark Tissue ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Orange Trees

The Asian citrus psyllid, Diaphorina citri Kuwayama, one of the known vectors for citrus greening disease or Huanglongbing (HLB) pathogens, has been present in Texas for over a decade, but the detection of the disease is recent. HLB has been confirmed in only two adjacent commercial citrus groves of grapefruit and sweet orange. A study was conducted to compare the population of Candidatus Liberibacter asiaticus (CLas) cells in different plant parts including peduncle, columella, leaves, seeds, young shoots, flower buds, flowers, and bark of 6-year-old known infected grapefruit and sweet orange trees. The bacterial population was estimated using a previously described grand universal regression equation Y = 13.82 – 0.2866X, where Y is the log of the target copy number and X is the Ct (threshold cycle) of the assay. Except for bark tissue, there was no significant difference in the concentration of CLas cells in other plant parts between the two cultivars. Within the cultivar, the bacterial concentration also varied with the plant part, with peduncle, columella, midrib having significantly higher titer of CLas compared with other plant parts. The obtained results here are in agreement with previous studies conducted on Florida samples, but the consistently lowest bacterial titer recorded in young shoots, leaf blade, and especially leaf margins relative to the midrib has never been previously reported.

scholarly journals Ground Application of Overdoses of Manganese Have a Therapeutic Effect on Sweet Orange Trees Infected with Candidatus Liberibacter asiaticus

HortScience ◽  
2019 ◽  
Vol 54 (6) ◽  
pp. 1077-1086 ◽  
Author(s):  
Flavia T. Zambon ◽  
Davie M. Kadyampakeni ◽  
Jude W. Grosser
Keyword(s):  
Therapeutic Effect ◽  
Sweet Orange ◽  
Quantitative Polymerase Chain Reaction ◽  
Therapeutic Effects ◽  
Tree Health ◽  
Rough Lemon ◽  
Canopy Volume ◽  
Liberibacter Asiaticus ◽  
Root Health ◽  
Orange Trees

There is accumulating evidence that root system collapse is a primary symptom associated with Huanglongbing (HLB)-induced tree decline, especially for commercial sweet orange and grapefruit trees on Swingle and Carrizo rootstocks. Maintaining root health is imperative to keep trees productive in an HLB-endemic environment. Preliminary greenhouse and field studies have shown that HLB-impacted trees had secondary and micronutrient deficiencies that were much greater in the roots than in the leaves, and that treatments containing three-times the recommended dose of manganese (Mn) improved tree health and growth and increased feeder root density in greenhouse trees. These results suggested that trees in an HLB-endemic environment have higher specific micronutrient requirements than those currently recommended. To test this hypothesis, established Vernia sweet orange grafted onto rough lemon rootstock trees were divided into eight supplemental CRF nutrition treatments (including two-times and four-times the recommended doses of Mn and boron) using a randomized complete block design in a commercial grove in St. Cloud, FL. The following supplemental nutrition treatments were used: no extra nutrition (control); Harrell’s–St. Helena mix 0.9 kg per tree; Harrell’s with 32 g of Florikan polycoated sodium borate (PSB) per tree; Harrell’s with 90 g of TigerSul® Mn sulfate (MS) per tree; Harrell’s with 32 g of PSB and 90 g of MS per tree; 180 g of MS per tree; 64 g of PSB per tree; and 180 g of MS plus 64 g of PSB per tree applied every 6 months since Fall 2015. Leaf and soil nutritional analyses were performed in Mar. 2017, Sept. 2017, and May 2018; a quantitative polymerase chain reaction was performed for Candidatus Liberibacter asiaticus (CLas) titer estimation in Nov. 2017. Significantly higher cycle threshold (Ct) values indicating reduced CLas bacterial populations were observed in trees that received the higher doses of Mn, especially those receiving four-times the recommended dosage of Mn (180 g Mn). Many trees exhibited Ct values of 32 or more, indicating a nonactive infection. Fruit yields of these trees were also increased. No significant differences in juice characteristics, canopy volume, and trunk section area were found between control plants and plants treated with 180 g Mn. Soil and leaf nutrients B, K, Mn, and Zn were significantly different among treatments at various times during the study. Our results strongly suggest that overdoses of Mn can suppress CLas bacterial titers in sweet orange trees on rough lemon rootstock, thus providing a therapeutic effect that can help restore tree health and fruit yields. This response was not observed when Mn and B were combined in the overdose, suggesting an antagonistic effect from B on Mn metabolism. When an overdose of Mn is used, biological functions and tree tolerance lost due to nutritional imbalances caused by HLB might be restored. Further studies are needed to elucidate which metabolic pathways are altered by comparing overdosed and conventionally fertilized HLB-impacted trees and to determine if the observed therapeutic effects can be achieved in trees grafted to other important commercial rootstocks.

Census of Candidatus Liberibacter asiaticus population inside the phloem of citrus trees

2020 ◽  
Author(s):  
Fernanda N.C. Vasconcelos ◽  
Jinyun Li ◽  
zhiqian pang ◽  
Christopher Vincent ◽  
Nian Wang
Keyword(s):  
Population Size ◽  
Sweet Orange ◽  
Bacterial Pathogens ◽  
Candidatus Liberibacter Asiaticus ◽  
Metabolic Burden ◽  
Whole Plant ◽  
Candidatus Liberibacter ◽  
Leaf Tissues ◽  
Liberibacter Asiaticus ◽  
Orange Trees

Candidatus Liberibacter asiaticus (CLas) is the predominant causal agent of citrus huanglongbing (HLB). The pathogen population size in local tissues and the whole plant are critical for the development of disease symptoms via pathogenicity factors and causing metabolic burden to the host. However, the total population size of CLas in a whole plant and the ratio of CLas vs. citrus cells in local tissues have not been addressed previously. The total CLas population size for 2.5-year-old Valencia sweet orange trees was quantified using quantitative PCR to be approximately 1.74 x 109, whereas that of 7 and 20-year-old sweet orange trees were estimated to be 4.3 x 1010, and 6.0 x 1010, respectively. The majority of CLas cells were distributed in the leaf tissues (55.58%), followed by that in the branch tissues (36.78%), feeder roots (4.75%), trunk (2.39%), and structural root (0.51%) tissues. The ratios of citrus cells vs. CLas cells for branch, leaf, trunk, feeder root, and structural root samples were approximately 39, 44, 153, 191, and 561, respectively, representing the metabolic burden of CLas in different organs. Approximately 0.01% of the total citrus phloem volume was estimated to be occupied by CLas. The CLas titer inside the leaf was estimated to be approximately 1.64 x 106 cells/leaf or 9.2 x 104 cells cm-2 in leaves, approximately 104 times less than that of typical apoplastic bacterial pathogens. This study provides quantitative estimates of phloem colonization by bacterial pathogens and further understands the biology and virulence mechanism of CLas.

scholarly journals Liberibacters Associated with Citrus Huanglongbing in Brazil: ‘Candidatus Liberibacter asiaticus’ Is Heat Tolerant, ‘Ca. L. americanus’ Is Heat Sensitive

Plant Disease ◽  
2009 ◽  
Vol 93 (3) ◽  
pp. 257-262 ◽  
Author(s):  
S. A. Lopes ◽  
G. F. Frare ◽  
E. Bertolini ◽  
M. Cambra ◽  
N. G. Fernandes ◽  
...  
Keyword(s):  
Sweet Orange ◽  
Sao Paulo ◽  
São Paulo ◽  
Candidatus Liberibacter Asiaticus ◽  
Paulo State ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
São Paulo State ◽  
Heat Tolerant ◽  
Orange Trees

In São Paulo State, Brazil, ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ are associated with huanglongbing (HLB). Affected municipalities occur mainly in the central and southern regions, where the annual number of hours above 30°C is two to five times lower than that in the extreme northern and western regions. The influence of temperature on sweet orange trees infected with ‘Ca. L. asiaticus’ or ‘Ca. L. americanus’ was studied in temperature-controlled growth chambers. Symptom progression on new shoots of naturally infected and experimentally graft-inoculated symptomatic sweet orange trees was assessed. Mottled leaves developed on all infected trees at 22 to 24°C, but not on any ‘Ca. L. americanus’–infected trees at 27 to 32°C. Quantitative, real time-PCR was used to determine the liberibacter titers in the trees. After 90 days, ‘Ca. L. asiaticus’–infected trees had high titers at 32 and 35°C, but not at 38°C, while ‘Ca. L. americanus’–infected trees had high titers at 24°C, but at 32°C the titers were very low or the liberibacters could not be detected. Thus, the multiplication of ‘Ca. L. asiaticus’ is not yet affected at 35°C, while a temperature of 32°C is detrimental to ‘Ca. L. americanus’. Thus, ‘Ca. L. americanus’ is less heat tolerant than ‘Ca. L. asiaticus’. The uneven distribution of these two liberibacters in São Paulo State might be in relation with these results.

scholarly journals Transmission Efficiency of Candidatus Liberibacter asiaticus and Progression of Huanglongbing Disease in Graft- and Psyllid-inoculated Citrus

HortScience ◽  
2014 ◽  
Vol 49 (3) ◽  
pp. 367-377 ◽  
Author(s):  
Ute Albrecht ◽  
David G. Hall ◽  
Kim D. Bowman
Keyword(s):  
Sweet Orange ◽  
Leaf Tissue ◽  
Transmission Efficiency ◽  
Pathogen Transmission ◽  
Transmission Frequency ◽  
Citrus Germplasm ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Polymerase Chain ◽  
Orange Trees

Candidatus Liberibacter asiaticus (Las) is a phloem-limited bacterium associated with huanglongbing (HLB), one of the most destructive diseases of citrus in Florida and other citrus-producing countries. Natural transmission of Las occurs by the psyllid vector Diaphorina citri, but transmission can also occur through grafting with diseased budwood. As a result of the difficulty of maintaining Las in culture, screening of citrus germplasm for HLB resistance often relies on graft inoculation as the mode of pathogen transmission. This study evaluates transmission efficiencies and HLB progression in graft-inoculated and psyllid-inoculated citrus under greenhouse and natural conditions in the field. Frequencies of transmission in graft-inoculated greenhouse-grown plants varied between experiments and were as high as 90% in susceptible sweet orange plants 6 to 12 months after inoculation. Transmission frequency in a tolerant Citrus × Poncirus genotype (US-802) was 31% to 75%. In contrast, transmission of Las after controlled psyllid inoculation did not exceed 38% in any of four experiments in this study. Whereas the time from inoculation to detection of Las by polymerase chain reaction (PCR) was faster in psyllid-inoculated US-802 plants compared with graft-inoculated US-802 plants, it was similar in graft- and psyllid-inoculated sweet orange plants. HLB symptom expression was indistinguishable in graft- and psyllid-inoculated plants but was not always associated with the number of bacteria in affected leaves. The highest number of Las genomes per gram leaf tissue measured in sweet orange plants was one to four × 107 in graft-inoculated plants and one to two × 107 in psyllid-inoculated plants. Highest numbers measured in tolerant US-802 plants were one to three × 106 and two to six × 106, respectively. Compared with artificial inoculation in a greenhouse setting, natural inoculation of field-grown sweet orange trees occurred at a much slower pace, requiring more than 1 year for infection incidence to reach 50% and a minimum of 3 years to reach 100%.

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