Fernando Rivas - Academia.edu (original) (raw)

Papers by Fernando Rivas

SN Applied Sciences

Citrus fruits and their by-products such as concentrated juices and essential oils are important ... more Citrus fruits and their by-products such as concentrated juices and essential oils are important intermediate by-products in the food industry that can selectively accumulate plant protection agrochemicals employed in their production. They are very difficult matrices for pesticide residue analysis due their high number and concentration of phytochemicals that could hamper the determinations. The fruit processing leads to the concentration/dilution or elimination of some of these natural products that change totally the nature of the matrix where the pesticides partition unevenly. Looking at the industrial process of the fruit, a unified vision for the pesticide residues analysis throughout the lemon fruit chain production, useful for the routine analysis of the above mentioned three matrices is presented. The driven concept is the minimization of matrix effects through sample dilution of the concentrated by-products, either after sample treatment or not. This approach will contribute to the maintenance of the whole instrumental system. QuEChERS AOAC 2007.01 was selected as the most suitable protocol for routine determination of, residues of 16 the pesticides most commonly used in the fruits during the citrus production through liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The same protocol was applied for pesticide residue analysis in concentrated juice after diluting 4 times the sample to minimize the matrix effects. For the analysis of lemon essential oils, the dilution and shoot procedure proved to be useful for LC-MS/MS and gas chromatography-mass spectrometry determination. The three methodologies were validated following SANTE guidelines, with quantitation limits below the established European Union and Codex Alimentarius maximum residue limits. The developed methodologies are useful tools for the routine control analysis of pesticide residues in lemon matrices, allowing high sample throughput and enhancing labs productivity.

Journal of Plant Pathology

Horticulturae

The dissipation of field-applied difenoconazole, imidacloprid, pyraclostrobin and spinosad on Cle... more The dissipation of field-applied difenoconazole, imidacloprid, pyraclostrobin and spinosad on Clementine mandarins (Citrus clementina Hort. ex Tan.) under controlled conditions throughout the citrus production chain was assessed. At harvest, 42 days after application, the dissipation of these pesticides were 80, 92, and 48% for difenoconazole, imidacloprid, pyraclostrobin, respectively, and spinosad was below the level of detectability. At day 28 after application, spinosad was no longer detected. The model equations that best describe the dissipation curves of these pesticides on Clementine mandarins showed different patterns. Their half-life on Clementine, calculated by the best-fitted experimental data, were 19.2 day (1st-order model) for difenoconazole, 4.1 day (Root Factor (RF) 1st-order model) for imidacloprid, 39.8 day (2nd-order model) for pyraclostrobin and 5.8 day (1st-order model) for spinosad. These results are the first record of pyraclostrobin persistence on mandarins,...

Fruticultura Profesional, 2007

Agrociencia Uruguay, 2010

... el hecho de que las GAs jue-gan un papel clave en el proceso de transición de flor a fruto (T... more ... el hecho de que las GAs jue-gan un papel clave en el proceso de transición de flor a fruto (Talón et al., 1992; Ben-Cheikh et al ... Las aplicaciones foliares de inhibidores de la síntesis de GAs se realizaron hasta punto de goteo, con pulverizador de presión manual a razón de 5 L ...

Biotecnologia Aplicada, Jun 1, 2013

An effi cient method for RNA extraction that leads to RNA high yield and purity is a technical is... more An effi cient method for RNA extraction that leads to RNA high yield and purity is a technical issue relevant for development and optimization of molecular diagnostic methods aimed to detect viroid infections in citrus varieties. Residual contaminants may affect RNA detection depending on the molecular diagnosis approaches. This condition can be evaluated through RNA absorption spectrum analysis. Functionally, it is assessed through observation of RT-PCR amplifi cation products and Northern blot and Dot-blot signal intensities, displaying levels of analytical response/ sensitivity. Four RNA extraction methods were evaluated to determine their effects on the capacity to detect viroid CEVd presence/absence in Citrus limon through four molecular diagnostic approaches: 1) conventional viroid extraction (CVE); 2) phenol/guanidine thiocyanate (PGT), 3) SDS/potassium acetate (SPA); and 4) formaldehyde/ SSC (FS). Phloem tissue quantifi cations showed values between 7500 ng/μL and 1200 ng/μL and ranged 1.3-2.0 OD 260/280. Evaluations through RT-PCR showed the expected amplifi cations of the entire CEVd genome, but erratic scenarios still remained. Non-radioactive probe hybridization techniques revealed high intensity signals (132 RU) for infected tissue, by using the CVE method, and a positivity cutoff for the presence of infection was established (78 RU). Nevertheless, molecular hybridization tools can jeopardize the diagnosis due to the thoroughness of the protocol and the RNA template conditions. The diagnostic ability of the association of Northern blot with CVE viroid extraction analyses as starting point was evidenced for successful detection, among the molecular methods tested.

Innotec Gestion, Apr 29, 2011

Cada día es mayor el cúmulo de datos sobre un área específica de actuación. Se habla del fenómeno... more Cada día es mayor el cúmulo de datos sobre un área específica de actuación. Se habla del fenómeno de infoxicación (Cornella, 2000) cuando se consumen grandes volúmenes de datos e informa-ción, en general de mala calidad. Adicionalmente, se presenta un desbalance ...

Food Chemistry, 2015

The degradation of the postharvest fungicides imazalil, orthophenylphenol, and pyrimethanil was s... more The degradation of the postharvest fungicides imazalil, orthophenylphenol, and pyrimethanil was studied on Clementine mandarins during packinghouse storage for a 28day period at 4°C. Fruits to which orthophenylphenol was applied, were treated with imazalil and pyrimethanil at doses of 1000 and 2000mgL(-1), using cascade application for the later and cascade and wax for the former. The decay of the three fungicides was evaluated using an in-house validated analytical procedure that includes the extraction and dispersive clean up of the samples followed by the GC-MS determination of the pesticide residues. The impact of fruit storage time on pesticide residues concentration was assessed. The residues found for the different application technologies were always below the established Maximum Residue Limits by the Codex Alimentarius and the European Union (5mgkg(-1) for imazalil, 7 and 8mgkg(-1) for pyrimethanil, and 10mgkg(-1) and 5mgkg(-1) for orthophenylphenol). The fungicides dissipated differentially. Pyrimethanil showed little degradation, if any, at both tested concentrations, but the half-life of imazalil on the fruit was 15-18days, independent of the application technology. Orthophenylphenol dissipated with a half-life of 15days. The initial imazalil residue found after cascade treatment was not significantly different between the doses studied (p<0.5), whereas when the fungicide was included in wax as an emulsifiable concentrate the initial and final imazalil residues were significantly different. Final residue levels after 28days of storage were 0.12-0.24mgkg(-1) for imazalil, 0.68mgkg(-1) for 2-phenylphenol and 0.56mgkg(-1) for pyrimethanil for all the evaluated treatments.

XII International Citrus Congress - International Society of Citriculture, 2015

Viruses, 2015

Citrus Tristeza Virus (CTV) is the most economically important virus of citrus worldwide. Genetic... more Citrus Tristeza Virus (CTV) is the most economically important virus of citrus worldwide. Genetic diversity and population structure of CTV isolates from all citrus growing areas from Uruguay were analyzed by RT-PCR and cloning of the three RNA silencing suppressor genes (p25, p20 and p23). Bayesian phylogenetic analysis revealed the circulation of three known genotypes (VT, T3, T36) in the country, and the presence of a new genetic lineage composed by isolates from around the world, mainly from South America. Nucleotide and amino acid identity values for this new genetic lineage were both higher than 97% for the three analyzed regions. Due to incongruent phylogenetic relationships, recombination analysis was performed using Genetic Algorithms for Recombination Detection (GARD) and SimPlot software. Recombination events between previously described CTV isolates were detected. High intra-sample variation was found, confirming the coexistence of different genotypes into the same plant. This is the first report describing: (1) the genetic diversity of Uruguayan CTV isolates circulating in the country and (2) the circulation of a novel CTV genetic lineage, highly present in the Viruses 2015, 7 4153 South American region. This information may provide assistance to develop an effective cross-protection program.

JOURNAL OF PLANT PATHOLOGY

The occurrence of Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viro... more The occurrence of Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus dwarfing viroid (CDVd), Citrus bark cracking viroid (CBCVd) and Citrus viroid VI (CVd-VI) in Citrus spp. cultivated in six provinces of Uruguay was surveyed in 2008- 2009 and 2009-2010 growing seasons using Northern blot hybridization. Sixty two per cent of surveyed trees were infected with either single or mixed viroid inocula, the latter being more abundant. CBCVd and CVd-VI were not detected in the samples analyzed. HSVd showed the highest prevalence (92%) among infected plants followed by CDVd (50%), CEVd (23%) and CBLVd (19%). The most frequently observed viroid combination was HSVd+CDVd. Our results showed that CEVd, CBLVd, HSVd, CDVd are widespread throughout citrus orchards in Uruguay and highlight the presence of mixed viroid infections.

Advances in Citrus Nutrition, 2012

Plant Science, 2006

The addition of 25 mg l À1 of CuSO 4 Á5H 2 O to the germination media significantly inhibited the... more The addition of 25 mg l À1 of CuSO 4 Á5H 2 O to the germination media significantly inhibited the in vitro pollen germination of 'Fortune' mandarin. Furthermore, when this was applied 8 h after in vitro germination it halted pollen tube development. The same concentration applied to 'Clemenules' mandarin flowers, at the preanthesis stage and 2 h prior to pollination with 'Fortune' mandarin pollen, arrested pollen tubes in the upper region of the style, and the average number of seeds per fruit was significantly reduced by 96%. Finally, 25 mg l À1 of CuSO 4 Á5H 2 O when applied at full bloom to entire 'Afourer' tangor trees under cross-pollination conditions, significantly reduced the average number of seeds per fruit by 55-81% and significantly increased the percentage of seedless fruits, without reducing fruit yield.

Environmental and Experimental Botany, 2008

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites... more The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old 'Loretina' mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.

Tree Physiology, 2007

Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohy... more Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohydrate concentration in various flowering and vegetative shoots were studied during natural fruit drop in two Citrus cultivars. Irrespective of shoot type, girdling delayed fruitlet abscission, but only fruitlets borne on leafy shoots had increased final fruit set. Chlorophyll a fluorescence analysis revealed differences in quantum yield efficiency of photosystem II of light adapted leaves (Φ PSII) among shoot types and in response to girdling. In young leaves of vegetative shoots, girdling decreased Φ PSII , whereas Φ PSII increased from Day 30 after girdling in young leaves of leafy flowering shoots; however, Φ PSII did not change in mature leaves during fruit set in either control or girdled trees. Girdling altered leaf carbohydrate concentrations and the photosynthetic performance of the various shoot types. Our results indicate that, in Citrus, several carbohydrate-based regulatory mechanisms of photosynthesis coexist during carbohydrate accumulation brought about by girdling. It is concluded that the delay in fruitlet abscission and the increase in Φ PSII observed in girdled leafy flowering shoots are the mechanisms underlying the enhancement of fruit set after girdling.

SN Applied Sciences

Citrus fruits and their by-products such as concentrated juices and essential oils are important ... more Citrus fruits and their by-products such as concentrated juices and essential oils are important intermediate by-products in the food industry that can selectively accumulate plant protection agrochemicals employed in their production. They are very difficult matrices for pesticide residue analysis due their high number and concentration of phytochemicals that could hamper the determinations. The fruit processing leads to the concentration/dilution or elimination of some of these natural products that change totally the nature of the matrix where the pesticides partition unevenly. Looking at the industrial process of the fruit, a unified vision for the pesticide residues analysis throughout the lemon fruit chain production, useful for the routine analysis of the above mentioned three matrices is presented. The driven concept is the minimization of matrix effects through sample dilution of the concentrated by-products, either after sample treatment or not. This approach will contribute to the maintenance of the whole instrumental system. QuEChERS AOAC 2007.01 was selected as the most suitable protocol for routine determination of, residues of 16 the pesticides most commonly used in the fruits during the citrus production through liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The same protocol was applied for pesticide residue analysis in concentrated juice after diluting 4 times the sample to minimize the matrix effects. For the analysis of lemon essential oils, the dilution and shoot procedure proved to be useful for LC-MS/MS and gas chromatography-mass spectrometry determination. The three methodologies were validated following SANTE guidelines, with quantitation limits below the established European Union and Codex Alimentarius maximum residue limits. The developed methodologies are useful tools for the routine control analysis of pesticide residues in lemon matrices, allowing high sample throughput and enhancing labs productivity.

Journal of Plant Pathology

Horticulturae

The dissipation of field-applied difenoconazole, imidacloprid, pyraclostrobin and spinosad on Cle... more The dissipation of field-applied difenoconazole, imidacloprid, pyraclostrobin and spinosad on Clementine mandarins (Citrus clementina Hort. ex Tan.) under controlled conditions throughout the citrus production chain was assessed. At harvest, 42 days after application, the dissipation of these pesticides were 80, 92, and 48% for difenoconazole, imidacloprid, pyraclostrobin, respectively, and spinosad was below the level of detectability. At day 28 after application, spinosad was no longer detected. The model equations that best describe the dissipation curves of these pesticides on Clementine mandarins showed different patterns. Their half-life on Clementine, calculated by the best-fitted experimental data, were 19.2 day (1st-order model) for difenoconazole, 4.1 day (Root Factor (RF) 1st-order model) for imidacloprid, 39.8 day (2nd-order model) for pyraclostrobin and 5.8 day (1st-order model) for spinosad. These results are the first record of pyraclostrobin persistence on mandarins,...

Fruticultura Profesional, 2007

Agrociencia Uruguay, 2010

... el hecho de que las GAs jue-gan un papel clave en el proceso de transición de flor a fruto (T... more ... el hecho de que las GAs jue-gan un papel clave en el proceso de transición de flor a fruto (Talón et al., 1992; Ben-Cheikh et al ... Las aplicaciones foliares de inhibidores de la síntesis de GAs se realizaron hasta punto de goteo, con pulverizador de presión manual a razón de 5 L ...

Biotecnologia Aplicada, Jun 1, 2013

An effi cient method for RNA extraction that leads to RNA high yield and purity is a technical is... more An effi cient method for RNA extraction that leads to RNA high yield and purity is a technical issue relevant for development and optimization of molecular diagnostic methods aimed to detect viroid infections in citrus varieties. Residual contaminants may affect RNA detection depending on the molecular diagnosis approaches. This condition can be evaluated through RNA absorption spectrum analysis. Functionally, it is assessed through observation of RT-PCR amplifi cation products and Northern blot and Dot-blot signal intensities, displaying levels of analytical response/ sensitivity. Four RNA extraction methods were evaluated to determine their effects on the capacity to detect viroid CEVd presence/absence in Citrus limon through four molecular diagnostic approaches: 1) conventional viroid extraction (CVE); 2) phenol/guanidine thiocyanate (PGT), 3) SDS/potassium acetate (SPA); and 4) formaldehyde/ SSC (FS). Phloem tissue quantifi cations showed values between 7500 ng/μL and 1200 ng/μL and ranged 1.3-2.0 OD 260/280. Evaluations through RT-PCR showed the expected amplifi cations of the entire CEVd genome, but erratic scenarios still remained. Non-radioactive probe hybridization techniques revealed high intensity signals (132 RU) for infected tissue, by using the CVE method, and a positivity cutoff for the presence of infection was established (78 RU). Nevertheless, molecular hybridization tools can jeopardize the diagnosis due to the thoroughness of the protocol and the RNA template conditions. The diagnostic ability of the association of Northern blot with CVE viroid extraction analyses as starting point was evidenced for successful detection, among the molecular methods tested.

Innotec Gestion, Apr 29, 2011

Cada día es mayor el cúmulo de datos sobre un área específica de actuación. Se habla del fenómeno... more Cada día es mayor el cúmulo de datos sobre un área específica de actuación. Se habla del fenómeno de infoxicación (Cornella, 2000) cuando se consumen grandes volúmenes de datos e informa-ción, en general de mala calidad. Adicionalmente, se presenta un desbalance ...

Food Chemistry, 2015

The degradation of the postharvest fungicides imazalil, orthophenylphenol, and pyrimethanil was s... more The degradation of the postharvest fungicides imazalil, orthophenylphenol, and pyrimethanil was studied on Clementine mandarins during packinghouse storage for a 28day period at 4°C. Fruits to which orthophenylphenol was applied, were treated with imazalil and pyrimethanil at doses of 1000 and 2000mgL(-1), using cascade application for the later and cascade and wax for the former. The decay of the three fungicides was evaluated using an in-house validated analytical procedure that includes the extraction and dispersive clean up of the samples followed by the GC-MS determination of the pesticide residues. The impact of fruit storage time on pesticide residues concentration was assessed. The residues found for the different application technologies were always below the established Maximum Residue Limits by the Codex Alimentarius and the European Union (5mgkg(-1) for imazalil, 7 and 8mgkg(-1) for pyrimethanil, and 10mgkg(-1) and 5mgkg(-1) for orthophenylphenol). The fungicides dissipated differentially. Pyrimethanil showed little degradation, if any, at both tested concentrations, but the half-life of imazalil on the fruit was 15-18days, independent of the application technology. Orthophenylphenol dissipated with a half-life of 15days. The initial imazalil residue found after cascade treatment was not significantly different between the doses studied (p<0.5), whereas when the fungicide was included in wax as an emulsifiable concentrate the initial and final imazalil residues were significantly different. Final residue levels after 28days of storage were 0.12-0.24mgkg(-1) for imazalil, 0.68mgkg(-1) for 2-phenylphenol and 0.56mgkg(-1) for pyrimethanil for all the evaluated treatments.

XII International Citrus Congress - International Society of Citriculture, 2015

Viruses, 2015

Citrus Tristeza Virus (CTV) is the most economically important virus of citrus worldwide. Genetic... more Citrus Tristeza Virus (CTV) is the most economically important virus of citrus worldwide. Genetic diversity and population structure of CTV isolates from all citrus growing areas from Uruguay were analyzed by RT-PCR and cloning of the three RNA silencing suppressor genes (p25, p20 and p23). Bayesian phylogenetic analysis revealed the circulation of three known genotypes (VT, T3, T36) in the country, and the presence of a new genetic lineage composed by isolates from around the world, mainly from South America. Nucleotide and amino acid identity values for this new genetic lineage were both higher than 97% for the three analyzed regions. Due to incongruent phylogenetic relationships, recombination analysis was performed using Genetic Algorithms for Recombination Detection (GARD) and SimPlot software. Recombination events between previously described CTV isolates were detected. High intra-sample variation was found, confirming the coexistence of different genotypes into the same plant. This is the first report describing: (1) the genetic diversity of Uruguayan CTV isolates circulating in the country and (2) the circulation of a novel CTV genetic lineage, highly present in the Viruses 2015, 7 4153 South American region. This information may provide assistance to develop an effective cross-protection program.

JOURNAL OF PLANT PATHOLOGY

The occurrence of Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viro... more The occurrence of Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus dwarfing viroid (CDVd), Citrus bark cracking viroid (CBCVd) and Citrus viroid VI (CVd-VI) in Citrus spp. cultivated in six provinces of Uruguay was surveyed in 2008- 2009 and 2009-2010 growing seasons using Northern blot hybridization. Sixty two per cent of surveyed trees were infected with either single or mixed viroid inocula, the latter being more abundant. CBCVd and CVd-VI were not detected in the samples analyzed. HSVd showed the highest prevalence (92%) among infected plants followed by CDVd (50%), CEVd (23%) and CBLVd (19%). The most frequently observed viroid combination was HSVd+CDVd. Our results showed that CEVd, CBLVd, HSVd, CDVd are widespread throughout citrus orchards in Uruguay and highlight the presence of mixed viroid infections.

Advances in Citrus Nutrition, 2012

Plant Science, 2006

The addition of 25 mg l À1 of CuSO 4 Á5H 2 O to the germination media significantly inhibited the... more The addition of 25 mg l À1 of CuSO 4 Á5H 2 O to the germination media significantly inhibited the in vitro pollen germination of 'Fortune' mandarin. Furthermore, when this was applied 8 h after in vitro germination it halted pollen tube development. The same concentration applied to 'Clemenules' mandarin flowers, at the preanthesis stage and 2 h prior to pollination with 'Fortune' mandarin pollen, arrested pollen tubes in the upper region of the style, and the average number of seeds per fruit was significantly reduced by 96%. Finally, 25 mg l À1 of CuSO 4 Á5H 2 O when applied at full bloom to entire 'Afourer' tangor trees under cross-pollination conditions, significantly reduced the average number of seeds per fruit by 55-81% and significantly increased the percentage of seedless fruits, without reducing fruit yield.

Environmental and Experimental Botany, 2008

The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites... more The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old 'Loretina' mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (F o) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms.

Tree Physiology, 2007

Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohy... more Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohydrate concentration in various flowering and vegetative shoots were studied during natural fruit drop in two Citrus cultivars. Irrespective of shoot type, girdling delayed fruitlet abscission, but only fruitlets borne on leafy shoots had increased final fruit set. Chlorophyll a fluorescence analysis revealed differences in quantum yield efficiency of photosystem II of light adapted leaves (Φ PSII) among shoot types and in response to girdling. In young leaves of vegetative shoots, girdling decreased Φ PSII , whereas Φ PSII increased from Day 30 after girdling in young leaves of leafy flowering shoots; however, Φ PSII did not change in mature leaves during fruit set in either control or girdled trees. Girdling altered leaf carbohydrate concentrations and the photosynthetic performance of the various shoot types. Our results indicate that, in Citrus, several carbohydrate-based regulatory mechanisms of photosynthesis coexist during carbohydrate accumulation brought about by girdling. It is concluded that the delay in fruitlet abscission and the increase in Φ PSII observed in girdled leafy flowering shoots are the mechanisms underlying the enhancement of fruit set after girdling.