Mature Grapefruit Research Articles

Trunk Injection of Oxytetracycline for Huanglongbing Management in Mature Grapefruit and Sweet Orange Trees.

Huanglongbing (HLB) is a devastating bacterial disease associated with 'Candidatus Liberibacter asiaticus'. The location of the pathogen within the vasculature of the tree has left growers with limited options for the effective management of the disease. Trunk injection is a crop protection technique that applies therapeutics directly into the xylem of woody tree species and allows for their systemic uptake and transport, which may provide more effective management of vascular diseases such as HLB. In this study, mature 'Valencia' and 'Hamlin' sweet orange (Citrus sinensis) and 'Duncan' grapefruit (C. paradisi) trees were injected with oxytetracycline (OTC) in the spring and/or fall to evaluate the effects of injection timing and response to injection. In addition to seasonal evaluations of tree health and bacterial titer, preharvest fruit drop, yield, and fruit quality were measured at harvest to determine the effects of OTC injection. The benefits associated with injection included a reduction in fruit drop, an increase in fruit yield and fruit size, and improvements in juice quality. However, results varied due to the timing of injection and were not consistent across all three varieties. Residue analysis at different time points after injection suggests that trunk injection effectively delivers therapeutics to mature citrus trees. This study provides fundamental information on the short-term benefits associated with trunk injection of OTC for HLB management in citrus groves. The potential for use of trunk injection at the commercial scale and the possible risks are discussed.

Effect of irrigation practices upon yield and fruit quality of four grapefruit (Citrus paradisiMac.) cultivars

AbstractTwo strategies of irrigation were applied during the phase of fruit growth in 30-year-old grapefruit trees (Citrus paradisi Mac.) of four varieties (cv. Marsh SRA 8, cv. Shambar SRA 22, cv. Frost Marsh, cv. Ruby). For the first strategy (T1), the trees were irrigated every week at 100% crop evapotranspiration (ETc), while for the second strategy (T2) at 60% ETc. At harvest time, tree yield was estimated along with fruit quality and water productivity. T1 strategy significantly increased the tree yield, the fruit weight and the juice content. Although an increase in water productivity (crop yield/total water use) was achieved during the water stress experiment for three out of the four varieties. The main effect of the T2 strategy was a significant increase of qualitative (commercial and nutritional) attributes like total soluble solids (TSS), citric acid, ascorbic acid (Vitamin C) and phenolic content. In addition, strategy T2 increased the maturation index and the fruits had sweeter flavor for two varieties. These results lead to the conclusion that in mature grapefruit trees, optimal irrigation practice provided better fruit yield, while water stress practices favor the accumulation of specific nutritional elements and improve specific fruit quality parameters, especially for cv. Ruby.

RAW MATERIALS IDENTIFICATION AND MANUFACTURED PRODUCTS AUTHENTICATION TECHNOLOGIES

DNA technologies for the raw grapes identification and the authentication of wine products made from them are popular scientific and practical direction with the prospect of introducing developments into the quality management system. The molecular genetic approaches development to the technical grape varieties’ genetic identification and wines DNA authentication produced from them was the aim of this work. Sample preparation of experimental wines was carried out by exposure in a mixture with a precipitant and a co-precipitant, followed by wine debris precipitation. The nucleic acids extraction from wine debris was carried out with the same commercial kit as from the pulp of a mature grape fruit, but with an additional lysis solution modification. The obtained results indicated the selected conditions effectiveness for sample preparation, DNA isolation and PCR for amplification of the analyzed Vitis vinifera L. UFGT-gene loci. The described strategy for the raw materials geno-identification and the manufactured products authentication is based on the polymorphic positions of diagnostically significant UFGT-gene-associated groups analysis, interpreted by sequencing the corresponding PCR product.

Application of partial rootzone drying to improve irrigation water use efficiency in grapefruit trees

Partial rootzone drying (PRD) has been reported to potentially improve crop water use efficiency (WUEcrop) compared to full irrigation in different fruit trees; however, field studies on the effect of PRD in citrus are scarce. In this field study, three irrigation strategies were tested in an orchard of mature grapefruit trees during two consecutive seasons (2013/2014 and 2014/2015): drip PRD (two drip lines, alternating irrigation between lines every month), microsprinkler irrigation, and double-line drip irrigation (control). Irrigation was applied during the fruit enlargement stage (April–August). The aims of this field study were: 1) to provide a quantitative comparison of irrigation water productivity among irrigation treatments; and 2) to study their effects on fruit quality, yield, tree growth, and flowering. Drip PRD saved 43 to 47% of irrigation water compared to control irrigation, and microsprinkler irrigation saved 12 to 18% of water compared to control irrigation PRD-irrigated trees maintained or increased yield compared to microsprinkler-irrigated and control trees, depending on the experimental season. Therefore, WUEcrop in PRD-irrigated trees was significantly higher than in control and microsprinkler-irrigated trees at the end of both seasons. Fruit and juice quality parameters were statistically similar among all treatments. PRD irrigation did not reduce the flowering potential of the trees although it delayed the onset of flowering in trees relative to the other treatments in 2013/2014. There was a similar timing of flowering among treatments in 2014/2015 and there were no differences in vegetative growth among the irrigation treatments by the end of March (86 Julian data) in both experimental seasons. Our results suggest that PRD can be economically beneficial for citrus growers who use double-line drip irrigation systems, and a strategy to sustain tree growth, tree health and yield during seasons of extreme drought or when high water restrictions are placed in citrus-producing areas.

Living on the Edges: Spatial Niche Occupation of Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), in Citrus Groves.

The spatial niche occupation of the Asian citrus psyllid, Diaphorina citri Kuwayama, 1908, was evaluated to determine its field colonization and food resource exploitation strategies in citrus groves. Mature grapefruit and sweet orange groves were surveyed as part of an area-wide program in 2009–2010 to determine D. citri population densities and between-tree distribution. In both cultivars, significantly more psyllids were found on perimeter trees throughout the study period suggesting a strong edge effect in D. citri distribution in the groves. D. citri densities and infestation levels gradually declined from the edge to the center of grove. Higher numbers of D. citri were recorded on trees located on the east and south sides of the groves than those on the west and north sides. Citrus groves located at the outer edge of the study with at least one side non-surrounded to other citrus groves harbored significantly more D. citri than groves located within the block cluster and entirely surrounded by other groves. In detailed field studies during 2012, infestation of D. citri started from border trees in the grove where possibly one generation is completed before inner trees become infested. In addition, psyllid densities decreased significantly with increasing distance from the grove edge. Using the selection index, D citri exhibited a strong niche occupation preference for border trees.

Copper Fungicide Spray Timings for Melanose Control in Grapefruit: Comparison of Computer Modelling of Copper Residues vs. Calendar Sprays

Grapefruit are susceptible to melanose from initial set until fruit diam. is 6-7 cm, which can span 3 months. Common Indian River melanose-control practice has been application of Cu fungicides at petal fall, with reapplication every three wks. through the infection period. Research data were previously used to develop a computer model to estimate Cu levels on fruit and indicate when reapplication is needed to prevent potential infection. The purpose of this study was to compare melanose control using spray timings suggested by the computer model vs. standard 3 week intervals vs. non-sprayed checks and was conducted over 3 years in mature grapefruit groves near Ft. Pierce, Fla. All applications were made using airblast at 1180 L· ha-1. Melanose and melanose-like Cu injury could not be distinguished and were combined in a melanose/Cu marking (MCM) score for each fruit. Separate fruit samples from the interior and exterior of tree canopies were randomly selected from each tree. In no year was there a significant difference in interior fruit MCM from computer model vs. calendar spray timings when treated with standard rates of Cu fungicide. However, rainfall never occurred when calendar-sprayed fruit were projected to be at low Cu levels. In 2 of 3 yrs. exterior fruit in the non-sprayed checks had less MCM than those from trees treated with Cu, indicating that Cu injury predominated over melanose on exterior fruit. In these fruit, MCM increased linearly with maximum fruit Cu concentration, which was lower on trees managed using the computer model. The computer model appears to be a sound approach to managing melanose, but economic benefit over calendar-based spray timing may only become apparent when practiced over numerous groves and seasons.

Economic Analysis of Aldicarb on Citrus in the Indian River Area in Southeastern Florida

Aldicarb is a pesticide used on several crops to control citrus rust mite (Phyllocoptruta oleivors), citrus nematode (Tylenchulus semipenetrans) and other citrus pests. Analysis of previous research experiments indicates that this pesticide is beneficial to both orange (Citrus sinensis) and grapefruit (Citrus parasisi) production and that both cost savings and higher yields can be experienced in many types of groves. Actual grove data shows that net returns for mature grapefruit that receive aldicarb can be $500/acre ($1235/ha) greater than net returns for identical acreage that uses other pest control options. Also, based on grove reset data, it is shown that with an application of aldicarb the resulting increased yields for 3-year-old trees more than cover the additional cost of applying the aldicarb.

Effects of early plant growth regulator treatments on flavonoid levels in grapefruit

Early foliar spray treatments containing gibberellic acid(GA3) significantly lower the concentration ofthe bitter flavonoid naringin in fruit tissues. Sprayscontaining a surfactant and different levels ofGA3 (5, 50, 100, and 500 ppm) or abscisic acid(ABA) (5, 25, and 50 ppm) were applied to young,developing fruit on mature grapefruit (Citrusparadisi) trees during the period from April to June,beginning just after fruit set. The fruit were allowedto mature and were harvested early the following year.Harvested fruit were evaluated for weight, juicecharacteristics, and flavonoid concentrations.GA3 application resulted in larger mature fruit,which yielded juice with the same soluble solids valueas juice from control fruit, but with slightly loweracid percentages and lower concentrations of naringin.ABA treatment had little effect on juice solublesolids, acid content and naringin content except atthe highest concentration of 50 ppm, which lowerednaringin levels slightly in juice.

Ethylene: A regulator of stress‐induced ACC synthase activity in nonclimacteric fruit

In spite of precautions, harvesting, packing and shimpping of grapefruit (Citrus paradisi) can often result in injury to the peel, which in turn leads to an increased evolution of the ripening hormone ethylene by the fruit. The present study is an attempt to determine how the stress‐induced ethylene pathway is regulated using the 1‐aminocyclopropane‐1‐carboxylate (ACC) synthase (EC 4.4.1.14) action inhibitor aminoethoxyvinylglycine (AVG). Incubation of mature grapefruit flavedo discs in the presence of AVG created a super‐induction of ACC synthase (ACS) activity. Maximum enzyme activity was achieved following an incubation period of between 24 and 36 h. From AVG‐treated flavedo discs, cDNA encoding ACS was isolated, employing reverse transcriptase‐polymerase chain reaction (RT‐PCR), and the accumulation of ACS transcripts, which peaked after 36 h incubation, was found to complement the recorded enzyme activity. Saturation of ACS activity was achieved with 100 μM AVG. Incubation of flavedo with AVG significantly decreased both the conversion of S‐adenosyl‐l‐methionine (AdoMet) to ACC and the evolution of ethylene from the treated tissue, and in vitro incubation of extracted ACS enzyme with AVG led to repression of the action of the enzyme. Treatment of flavedo discs with ACC and ethylene inhibited the AVG‐induced ACS activity. Northern blot analysis showed that ethylene sumppressed the accumulation of ACS mRNA. It is suggested that in nonclimacteric fruit, the synthesis of ethylene can be regulated through a process of autoinhibition working at the level of gene expression.

Purification and Characterization of a Polygalacturonase-inhibiting Protein from Grapefruit Flavedo

Polygalacturonase-inhibiting proteins (PGIPs) are believed to be one component of plants inherent defense mechanisms against fungal pathogens. We have purified a PGIP from mature grapefruit (Citrus paradisi cv. Marsh) flavedo using ammonium sulfate precipitation, preparative isoelectric focusing and ion exchange chromatography. Two peaks of PGIP activity were separated by isoelectric focusing, one at pH 6–7 and one at pH 9–10. The basic protein was more abundant than the neutral protein and was selected for further purification. The basic protein binds to S Sepharose at pH 6.1 and has an apparent Mr of ≈43,000 based on SDS-PAGE analysis. The protein is glycosylated as revealed by binding to ConA sepharose and is serologically similar to PGIPs from bean hypocotyl and pear fruit. Two dimensional PAGE analysis revealed the presence of two bands of similar Mr but with slightly different pIs (≈9.0–9.5). The N-terminal amino acid sequence of grapefruit PGIP shows high homology with PGIPs from fruit of other species and with a cDNA clone of PGIP that was isolated from a Citrus sinensis cv. Hamlin expression library. Grapefruit PGIP inhibits polygalacturonases from Aspergillus niger, and the citrus pathogen Penicillium italicum. We are interested in the role of PGIP in resistance of citrus fruit to postharvest decay fungi.

Reclaimed Wastewater for Irrigation of Citrus in Florida

Reclaimed municipal wastewater has been used to irrigate young and mature sweet orange and grapefruit trees in Florida. In the central ridge area of Florida, trees receiving reclaimed wastewater had greater yields and improved tree vigor compared to trees receiving wellwater. The high level of reclaimed wastewater applied (2.54 cm/week), however, decreased fruit total soluble solids, acids, and their ratio. In contrast, tree vigor and fruit quality were not different for mature grapefruit trees growing in the coastal, flatwoods area of Florida, which received reclaimed wastewater or canal water. Yields, however, were higher for the reclaimed wastewater treatments in one season, but the effect was variable. No adverse effects of applying high levels of reclaimed wastewater were noted at either site. The use of reclaimed wastewater for citrus irrigation has potential benefits for Florida citrus growers in the future.

Seasonal Patterns Associated withTylenchulus semipenetransandPhytophthora parasiticain the Citrus Rhizosphere

Populations of Tylenchulus semipenetrans and Phytophthora parasitica were measured weekly during 27 mo in an orchard of mature grapefruit trees on rough lemon rootstock in the central ridge region of Florida. The study was conducted to identify potential key climatic and host factors affecting population changes in both parasites. Patterns of change in root mass density and concentrations of root lignin and nonstructural carbohydrate suggested annual as well as seasonal variation in the age structure and nutritional value of the fibrous root system. Numbers of nematode females on roots and juveniles and males in soil were related positively (P=0.01) to root mass density and root concentration of reducing sugars, starch, and total nonstructural carbohydrates [...]

Effects of Shape and Size of Colored Traps on Attractiveness to Irradiated, Laboratory-Strain Mexican Fruit Flies (Diptera: Tephritidae)

Twenty-four trap types representing all combinations of 4 colors, 3 shapes and 2 sizes were evaluated for visual attractiveness to irradiated, laboratory-reared Mexican fruit flies, Anastrepha ludens (Loew), released into a grapefruit orchard when 1-3 days old. Spheres and vertically oriented rectangular panels were not significantly different in attractiveness summed over spring, summer and autumn seasons. Horizontally oriented rectangles were much less attractive than spheres and vertical rectangles. Larger rectangles (13 by 18 cm) and spheres (13 cm diam.) were more attractive than smaller rectangles (10 by 13 cm) and spheres (8 cm diam.). Yellow, green and red were equally attractive summed over trap shapes, sizes and seasons. Red was less attractive than green in spring and summer but more attractive in autumn. Relative attractiveness of yellow compared to green was less affected by season. Overall, vertical rectangles were more attractive than spheres in spring while spheres were more attractive in autumn. In spring, red spheres were more attractive than vertical red rectangles while yellow and white rectangles were more attractive than yellow and white spheres. Traps in trees with mature grapefruit generally captured more flies than those in trees with only small, immature fruit. Small spheres were more attractive than small vertical rectangles to females in trees with small, immature fruit but were less attractive than small vertical rectangles in trees with mature fruit. Overall, the best traps were the large sizes of the 6 combinations of yellow, green and red spheres and vertical rectangles that captured 8 times as many flies as the least attractive traps.

Phase Change in Citrus: Immunologically Detectable Differences Between Juvenile and Mature Plants

Homogenates prepared from mature and juvenile grapefruit (Citrus paradisi Macf. cv. Marsh) were used to raise antibodies in rabbits. The resultant polyvalent antisera were subjected to immunoadsorption and selection techniques. A specific antiserum was obtained which reacted with an antigenic protein found in greater quantities in tissues of mature Citrus plants than in tissues of juvenile plants. This is referred to as the 'mature' protein. The 'mature' protein is resistant to temperatures of up to 80ºC, and has a molecular weight of approximately 59.7 kDa. The protein is found in Citrus species, but not in the closely related genera Poncirus, Microcitrus or Fortunella. It is not found in the other plant species studied. The mature protein content increases in the leaves towards the apex of single-stemmed seedlings, and in the floral shoots of precociously flowering Marsh grapefruit seedlings. There are few morphological or chemical characters which change concurrently with the achievement of maturity in citrus seedlings, and none is well suited as a predictor of phase change. The identification of a protein marker associated with phase change has important implications, both in the understanding of the processes of phase change, and in the practical field of plant breeding.

Uptake of 14C‐gibberellic acid by mature grapefruit (Citrus paradisi Macf.) as affected by relative humidity and method of application

SummaryEffects of the method of application and relative humidity on the uptake of 14C‐gibberellic acid (14C‐GA3) by mature grapefruit (Citrus paradisi Macf.) were examined. Uptake was higher when 14C‐GA3 was applied as a ‘drying‐out’ solution than as a ‘non‐drying’ solution. When 14C‐GA, was applied by the ‘drying‐out’ method, which closely imitates field conditions, rates of uptake were very high while the solution was drying out and during the first few hours after drying. Uptake from the dry residue continued in decreasing rates till the end of the experiment (72 h). Uptake from the dry residue was higher when fruits were incubated at 100% than at 50% relative humidity (RH). Transfer of fruits from 50% to 100% RH as late as 48 h after drying still increased the rate of uptake. Drying‐out treatment solutions produced higher uptake rates with neutral (pH 7) as well as acid (pH 4) treatment solutions, and in the presence of triton B‐1956, Triton X‐100 or L‐77 surfactants.

An approach to determine concrete-failure softening curves

Partial rootzone drying (PRD) has been reported to potentially improve crop water use efficiency (WUEcrop) compared to full irrigation in different fruit trees; however, field studies on the effect of PRD in citrus are scarce. In this field study, three irrigation strategies were tested in an orchard of mature grapefruit trees during two consecutive seasons (2013/2014 and 2014/2015): drip PRD (two drip lines, alternating irrigation between lines every month), microsprinkler irrigation, and double-line drip irrigation (control). Irrigation was applied during the fruit enlargement stage (April–August). The aims of this field study were: 1) to provide a quantitative comparison of irrigation water productivity among irrigation treatments; and 2) to study their effects on fruit quality, yield, tree growth, and flowering. Drip PRD saved 43 to 47% of irrigation water compared to control irrigation, and microsprinkler irrigation saved 12 to 18% of water compared to control irrigation PRD-irrigated trees maintained or increased yield compared to microsprinkler-irrigated and control trees, depending on the experimental season. Therefore, WUEcrop in PRD-irrigated trees was significantly higher than in control and microsprinkler-irrigated trees at the end of both seasons. Fruit and juice quality parameters were statistically similar among all treatments. PRD irrigation did not reduce the flowering potential of the trees although it delayed the onset of flowering in trees relative to the other treatments in 2013/2014. There was a similar timing of flowering among treatments in 2014/2015 and there were no differences in vegetative growth among the irrigation treatments by the end of March (86 Julian data) in both experimental seasons. Our results suggest that PRD can be economically beneficial for citrus growers who use double-line drip irrigation systems, and a strategy to sustain tree growth, tree health and yield during seasons of extreme drought or when high water restrictions are placed in citrus-producing areas.

Grapefruit Leaf and Fruit Growth in Response to Drip, Microsprinkler, and Overhead Sprinkler Irrigation

Abstract Fruit and vegetative growth of 21-year-old grapefruit (Citrus paradisi Macf.) trees on well-drained sandy soil was studied in central Florida. Drip, microsprinkler, and overhead sprinkler irrigation was compared at two levels of irrigation (150 and 450 mm·year−1). Significant differences in leaf area, fruit size, fruit growth, new flush growth, and canopy area were found with different irrigation systems applying similar amounts of water. Growth was improved by irrigation even in a year of high rainfall (1410 mm). With mature trees, drip systems promoted the least growth, while overhead sprinkler systems promoted the most. Leaf fresh and dry weights and individual leaf areas in the overhead sprinkler treatments were 40% to 50% greater than in the drip or nonirrigated treatments, while specific leaf weight and leaf water content per unit dry weight were similar for all treatments. Final fruit size and tree canopy area were 9% to 20% greater in the overhead sprinkler treatments than in the corresponding drip or nonirrigated treatments. Responses to microsprinklers were generally intermediate between the overhead sprinkler and the drip treatments. Because of the low soil area coverage, applying water at the higher rate with the drip system did not improve growth as well as the overhead system at the lower rate. With mature grapefruit trees under central Florida conditions, systems providing greater soil area coverage gave better leaf and fruit growth than systems providing less soil coverage.

The effect of high sodium irrigation water on soil salinity and yield of mature grapefruit orchard

Citrus is considered to be specifically sensitive to chloride and sodium, yet little data exist to show the effect of these ions on yield. An experiment was started in 1978 to study the effect of sodic irrigation water on yield. The treatments were SAR of the irrigation water of 2.8-(L), 5.5-(M), and 10.3-(H) (mol/m3)1/2\(({\text{SAR = Na}}^{\text{ + }} /\sqrt {{\text{Ca}}^{{\text{ + + }}} {\text{ + Mg}}^{{\text{ + + }}} /2} )\). The experiment follows a study on the same plots using irrigation water of variable chloride concentration and a uniform SAR of 4.2 (mol/m3)1/2.

The effect of partial wetting of the root zone on yield and water use efficiency in a drip-and sprinkler-irrigated mature grapefruit grove

The effect of partial wetting of the root zone on yield and water use efficiency in a drip- and sprinkler-irrigated mature grapefruit grove was tested in a long-term experiment from 1976 to 1979. Three different percentages of the surface soil areas (∼ 30%, 40% and 70%) were wetted by the use of single and double drip laterals and sprinklers, respectively. Irrigation frequencies were 3 and 7 days for the drip treatments and 14 and 21 days for the sprinkler-irrigated plots.

Grapefruit response to variable salinity in irrigation water and soil

Results are reported from a long-term field experiment designed to determine the effect of irrigation water salinity on the yield and water uptake of mature grapefruit trees. Treatments were started in 1970 and consisted of chloride concentrations in the irrigation water of 7.1, 11.4 and 17.1 meq/1 added as NaCl+CaCl2 at a 1 : 1 weight ratio.