Abstract
Previous research has shown that Huanglongbing {HLB [causal agent Candidatus Liberibacter asiaticus ( C Las)]}-affected sweet orange ( Citrus sinensis ) trees have a reduced root-to-shoot ratio, potentially due to the high rate of root death. The diminished root system cannot support the existing aboveground canopy and a cycle of imbalance begins. As a result, the tree enters into a continuous carbohydrate stress cycle and, eventually, the tree declines. Therefore, the goal of this study was to evaluate pruning as a strategy to adjust the root-to-shoot ratio to improve growth and productivity of HLB-affected trees. In Jan. 2015, a 3-year trial was initiated on a 14-year-old grove of ‘Hamlin’ sweet orange on Swingle citrumelo ( Citrus paradisi × Poncirus trifoliate ) rootstock that was symptomatic of HLB and produced less than 180 lb of fruit per tree. The four pruning treatments were as follows: 1) 0% pruning (no canopy removal), 2) 25% pruning (canopy removed), 3) 50% pruning (canopy removed), and 4) 80% pruning (canopy removed). In a split-plot design, two sources of fertilizer were evaluated in combination with the pruning: 1) conventional fertilizer [CNV (dry granular)] applied at 200 lb/acre nitrogen (N) in five split applications per year, and 2) controlled-release fertilizer (CRF) applied at 150 lb/acre N, split in three applications per year. Within each pruning treatment, half of the trees received CNV and the other half received CRF. The fertilizer treatments were applied in each of the 3 years; however, pruning was performed only once in the beginning of the experiment. The trees that were pruned produced new vegetative growth that looked healthy with no visual HLB symptoms (initially); however, the trees remained positive for CLas throughout the study as determined by quantitative real-time polymerase chain reaction. The 80% pruned trees grew vigorously over the course of 3 years but remained significantly smaller in canopy than control trees (0% pruning) for both CRF and CNV treatments. The 25% and 50% pruned tree canopies grew back and were similar in canopy size as 0% pruning (control) treatment by the end of year 2. At the end of the study, the use of CRF on 25% pruned trees resulted in a significantly higher leaf area index as compared with trees receiving CNV. A significant positive linear correlation was observed between canopy volume and root density; the root density decreased with intensive pruning. A significant positive correlation was also observed between canopy volume and yield, and a negative correlation between canopy volume and fruit drop. There were no significant increases in yield resulting from any pruning or fertilization treatments compared with controls (0% pruning). However, with the use of CRF, the amount of N and frequency of application were reduced. Overall, our results indicate that pruning did not improve the productivity of HLB-affected trees over the course of 3 years. Therefore, severe pruning is not a viable option to rejuvenate the HLB-affected trees.
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Claims 13
Claim · model-written summary
The 80% pruned trees stayed significantly smaller in canopy than unpruned control trees over three years.
- Taxon
- Sweet Orange
Citrus sinensist1 - Treatment
- 80% prunede1
- Outcome
- canopye1
- Direction
- smallere1
- Qualifier
- for both CRF and CNV treatmentse1
- Comparator
- control trees (0% pruning)e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“The 80% pruned trees grew vigorously over the course of 3 years but remained significantly smaller in canopy than control trees (0% pruning) for both CRF and CNV treatments”
Claim · model-written summary
The 25% and 50% pruned canopies were similar in size to unpruned controls by the end of year 2.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- 25% and 50% prunede1
- Outcome
- canopy sizee1
- Direction
- similare1
- Qualifier
- by the end of year 2e1
- Comparator
- 0% pruning (control) treatmente1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“The 25% and 50% pruned tree canopies grew back and were similar in canopy size as 0% pruning (control) treatment by the end of year 2”
Claim · model-written summary
At the end of the study, CRF on 25% pruned trees gave a significantly higher leaf area index than CNV.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- use of CRF on 25% pruned treese1
- Outcome
- leaf area indexe1
- Direction
- highere1
- Qualifier
- At the end of the studye1
- Comparator
- trees receiving CNVe1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“At the end of the study, the use of CRF on 25% pruned trees resulted in a significantly higher leaf area index as compared with trees receiving CNV”
Claim · model-written summary
Canopy volume and root density were positively and linearly correlated.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- canopy volumee1
- Outcome
- root densitye1
- Direction
- positive linear correlatione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“A significant positive linear correlation was observed between canopy volume and root density”
Claim · model-written summary
Root density decreased with intensive pruning.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- intensive pruninge1
- Outcome
- root densitye1
- Direction
- decreasede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“the root density decreased with intensive pruning”
Claim · model-written summary
Canopy volume was positively correlated with yield.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- canopy volumee1
- Outcome
- yielde1
- Direction
- positive correlatione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“A significant positive correlation was also observed between canopy volume and yield”
Claim · model-written summary
Canopy volume was negatively correlated with fruit drop.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- canopy volumee1
- Outcome
- fruit drope1
- Direction
- negative correlatione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“a negative correlation between canopy volume and fruit drop”
Claim · model-written summary
No pruning or fertilization treatment significantly increased yield compared with unpruned controls.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- any pruning or fertilization treatmentse1
- Outcome
- yielde1
- Direction
- no significant increasese1
- Comparator
- controls (0% pruning)e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“There were no significant increases in yield resulting from any pruning or fertilization treatments compared with controls (0% pruning)”
Claim · model-written summary
CRF reduced the amount of N applied and the frequency of application.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- CRFe1
- Outcome
- amount of N and frequency of applicatione1
- Direction
- reducede1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“with the use of CRF, the amount of N and frequency of application were reduced”
Claim · model-written summary
Pruning did not improve productivity of HLB-affected trees over three years.
- Taxon
- Sweet OrangeCitrus sinensist1
- Treatment
- pruninge1
- Outcome
- productivitye1
- Direction
- did not improvee1
- Qualifier
- over the course of 3 yearse1
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“pruning did not improve the productivity of HLB-affected trees over the course of 3 years”
Claim · model-written summary
Pruned trees remained positive for CLas throughout the study.
- Taxon
- Sweet OrangeCitrus sinensist1
- Interactor
- CLase1pathogen
- Outcome
- remained positive for CLase1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e0“causal agent Candidatus Liberibacter asiaticus ( C Las)”
e1“the trees remained positive for CLas throughout the study”
Claim · model-written summary
Pruned trees produced new vegetative growth that looked healthy with no visual HLB symptoms initially.
- Taxon
- Sweet OrangeCitrus sinensist1
- Outcome
- new vegetative growthe1
- Qualifier
- looked healthy with no visual HLB symptoms (initially)e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“new vegetative growth that looked healthy with no visual HLB symptoms (initially)”
Claim · model-written summary
Severe pruning is not a viable option to rejuvenate HLB-affected trees.
- Taxon
- Sweet OrangeCitrus sinensist1
- Outcome
- severe pruning is not a viable option to rejuvenatee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t1“Sweet Orange”
e1“severe pruning is not a viable option to rejuvenate the HLB-affected trees”
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