Abstract
Crop protection measures, cultural practices, nutrient and irrigation management, rootstock selection, and other studies have been conducted to alleviate the devastating bacterial disease of Huanglongbing (HLB; also known as citrus greening) in recent years. However, there is no single cure for HLB caused by Candidatus Liberibacter asiaticus ( C Las), which is spread by the Asian citrus psyllid Diaphorina citri Kuwayama . The objectives of the study were to assess whether tree growth, soil and leaf tissue nutrient concentrations, fruit yield, and postharvest quality can be improved through improved nutrient management of sweet orange grown on selected rootstocks. The study of ‘Hamlin’ citrus trees [ Citrus sinensis (L.) Osbeck] budded on Cleopatra mandarin ( Citrus reshni ) or Swingle rootstocks [ Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] was conducted from 2019 to 2021. The study was conducted in a split-plot design with two rootstocks as main plots, three nitrogen (N) rates (168, 224, and 280 kg·ha −1 ) as sub-plots, and secondary macronutrients [control, calcium (Ca), or magnesium (Mg) thiosulfates at 45 kg·ha −1 each and a combination of Ca and Mg at 22.5 kg·ha −1 each)] as a sub-subplots replicated four times. Results indicated that soil ammonium nitrogen (NH 4 -N) and nitrate nitrogen (NO 3 -N) significantly accumulated in an oscillating (between spring and summer seasons) pattern for soil NH 4 -N and a persistent accumulation of NO 3 -N on both rootstocks over time from <1.0 mg·kg −1 at the beginning; thereafter, it stabilized at approximately 4.0 mg·kg −1 on both rootstocks. Citrus trees budded on Swingle rootstocks responded to macronutrient applications more than those on Cleopatra rootstocks. Leaf micronutrients [manganese (Mn) and zinc (Zn)], as opposed to leaf boron (B), iron (Fe), and copper (Cu) concentrations, were within the lowest ranges. Hence, supplementary micronutrients (Mn and Zn) are a mandatory cultural practice for HLB-affected Hamlin citrus trees. Control trees had a lower leaf area index (LAI) than those that received either Ca and/or Mg treatments, and the impact was significant on Swingle, rather than on Cleopatra, rootstocks. Trees on Cleopatra were inherently greater in canopy volume compared with Swingle rootstocks. However, the impact of secondary macronutrients manifested only after the third year of the study. Fruit yield significantly increased by a magnitude of 1.8-times in the trees that received combined Ca and Mg treatments compared with control trees. Greater total soluble solids were observed in trees that received Mg or combined Ca and Mg treatments. Thus, we conclude that nutrient management enhanced tree growth, fruit yield, and postharvest quality and should be considered as an immediate solution for mitigating HLB until it can be permanently cured or eradicated.
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Claims 12
Claim · model-written summary
Soil ammonium nitrogen accumulated in an oscillating spring-summer pattern on both rootstocks.
- Taxon
- sweet orange
Citrus sinensist0 - Outcome
- soil NH 4 -Ne0
- Direction
- accumulatede0
- Qualifier
- between spring and summer seasonse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil ammonium nitrogen (NH 4 -N) and nitrate nitrogen (NO 3 -N) significantly accumulated in an oscillating (between spring and summer seasons) pattern for soil NH 4 -N”
t0“Sweet Orange”
Claim · model-written summary
Soil nitrate nitrogen accumulated persistently on both rootstocks, then stabilized near 4.0 mg·kg −1.
- Taxon
- sweet orangeCitrus sinensist0
- Outcome
- NO 3 -Ne0
- Direction
- accumulatione0
- Value
- 4.0 mg·kg −1e0
- Qualifier
- <1.0 mg·kg −1 at the beginninge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a persistent accumulation of NO 3 -N on both rootstocks over time from <1.0 mg·kg −1 at the beginning; thereafter, it stabilized at approximately 4.0 mg·kg −1”
t0“Sweet Orange”
Claim · model-written summary
Swingle-rootstock trees responded more to macronutrients than Cleopatra-rootstock trees.
Verbatim
e0“Citrus trees budded on Swingle rootstocks responded to macronutrient applications more than those on Cleopatra rootstocks”
Claim · model-written summary
Leaf manganese and zinc concentrations were within the lowest ranges.
- Taxon
- sweet orangeCitrus sinensist0
- Outcome
- Leaf micronutrients [manganese (Mn) and zinc (Zn)]e0
- Direction
- loweste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaf micronutrients [manganese (Mn) and zinc (Zn)], as opposed to leaf boron (B), iron (Fe), and copper (Cu) concentrations, were within the lowest ranges”
t0“Sweet Orange”
Claim · model-written summary
The authors recommend supplementary manganese and zinc for HLB-affected Hamlin trees.
Verbatim
e0“supplementary micronutrients (Mn and Zn) are a mandatory cultural practice for HLB-affected Hamlin citrus trees”
Claim · model-written summary
Calcium or magnesium treatments increased leaf area index relative to controls, significantly on Swingle rootstocks.
Verbatim
e0“Control trees had a lower leaf area index (LAI) than those that received either Ca and/or Mg treatments, and the impact was significant on Swingle, rather than on Cleopatra, rootstocks”
Claim · model-written summary
Cleopatra-rootstock trees had greater canopy volume than Swingle-rootstock trees.
Verbatim
e0“Trees on Cleopatra were inherently greater in canopy volume compared with Swingle rootstocks”
Claim · model-written summary
Secondary macronutrient effects manifested only after the third study year.
- Taxon
- sweet orangeCitrus sinensist0
- Outcome
- impact of secondary macronutrientse0
- Qualifier
- after the third year of the studye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the impact of secondary macronutrients manifested only after the third year of the study”
t0“Sweet Orange”
Claim · model-written summary
Combined calcium and magnesium increased fruit yield 1.8-times versus controls.
Verbatim
e0“Fruit yield significantly increased by a magnitude of 1.8-times in the trees that received combined Ca and Mg treatments compared with control trees”
Claim · model-written summary
Magnesium treatment produced greater total soluble solids.
Not reportedComparator
Verbatim
e0“Greater total soluble solids were observed in trees that received Mg or combined Ca and Mg treatments”
Claim · model-written summary
Combined calcium and magnesium produced greater total soluble solids.
Not reportedComparator
Verbatim
e0“Greater total soluble solids were observed in trees that received Mg or combined Ca and Mg treatments”
Claim · model-written summary
The authors recommend nutrient management as an immediate HLB mitigation measure.
- Taxon
- sweet orangeCitrus sinensist0
- Outcome
- nutrient managemente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“nutrient management enhanced tree growth, fruit yield, and postharvest quality and should be considered as an immediate solution for mitigating HLB”
t0“Sweet Orange”
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