Star Ruby Research Articles

Effects of hot water dip or heat conditioning of ‘Star Ruby’ grapefruit quality during quarantine treatment and simulated storage duration

Effects of hot water dip or heat conditioning of ‘Star Ruby’ grapefruit quality during quarantine treatment and simulated storage duration

Investigation of chromoplast ultrastructure and tissue-specific accumulation of carotenoids in citrus flesh

Citrus flesh color due to the accumulation of carotenoids in chromoplasts is one of the most important traits for breeding. However, the relationship between carotenoids and chromoplast ultrastructure in citrus is largely unclear. Thus, in this study fourteen representative citrus cultivars including those with yellow, orange, and red flesh were comparatively analyzed by light microscopy, exhibiting three types of chromoplasts (i.e. globular, fusiform and crystalloid). Significant differences in carotenoid content and cell wall thickness were found in sub-divided tissues of three grapefruits by high performance liquid chromatography and transmission electron microscopy. Based on our findings, it could be inferred that the accumulation of lycopene was closely related to the formation of crystalline chromoplasts. In the meantime, 'Flame' grapefruit with high content of carotenoids and cells with thin cell wall would have greater bio-accessibility, which indicated that 'Flame' grapefruit was superior to 'Star Ruby' grapefruit in the processing of citrus pulp juice. In conclusion, bio-accessibility influenced by chromoplasts and cell wall should be taken into consideration in citrus nutritional breeding, and differences in carotenoid accumulation and chromoplast morphology with tissue-specific characteristics would provide a new insight for further research.

Influence of the storage temperature on volatile emission, carotenoid content and chilling injury development in Star Ruby red grapefruit

Grapefruits are sensitive to develop chilling injury (CI) on the peel upon postharvest storage at low temperature. We investigated the influence of the storage at 2 and 12 °C on CI, carotenoids, and emission of volatiles by intact fruit. CI symptoms at 12 °C were restricted to green fruit peel sectors but at 2 °C the CI severity was higher and distributed through the whole fruit surface. Fruit peel coloration and carotenes content increased at 12 °C whereas experienced minor changes at 2 °C. At 2 °C the emission of total volatiles and specific monoterpenes, mainly limonene, but also linalool and α-terpineol was enhanced, while storage at 12 °C resulted in higher emission and diversity of cyclic sesquiterpenes and aliphatic esters. Results indicate a selective emission of volatiles by intact red grapefruit that appears to be a specific response to the storage temperature or to the cold-induced damage.

Effects of 2,4-DP- P (2,4-Dichlorophenoxypropionic Acid-P) Plant Growth Regulator on Fruit Size and Yield of Star Ruby Grapefruit (Citrus paradisi Osb.)

Star Ruby is the main grapefruit (Citrus paradisi) variety grown in Turkey; however, small fruit size is a common problem in ‘Star Ruby‘ grapefruit. Fruit size is a decisive external quality parameter in citrus at the marketing of fresh citrus fruits. Fruit size can be enhanced by several techniques such as girdling and thinning. Various plant growth regulators are known to affect the growth and size of citrus fruit. The objective of the present study was to observe the effects of 2,4 dichlorophenoxypropionic acid-p (2,4-DP-P) on the fruit size, yield and quality of Star Ruby from 20-year-old trees budded on sour orange rootstock in Adana, Turkey in 2007. Four concentrations (50, 100, 150 and 300 ppm) of 2,4-DP-P were applied 8 weeks after anthesis during physiological fruit drop when the mean fruit diameter was 13-15 mm. The results indicated that the application of 2,4-DP-P increased the fruit size of Star Ruby grapefruit without reducing yield. The application had a significant effect on fruit yield except for trees treated with 50 ppm 2,4-DP-P. Compared with the control trees, applications of 2,4-DP-P increased the number of large, commercially valuable Star Ruby (>93 mm, 89-93 mm and 84-89 mm). No effects were determined on fruit internal quality parameters. Thus, the results of the present study revealed that 2,4-DP-P can be used to improve the fruit size of Star Ruby fruitlets during the June drop.

Survey of Citrus tristeza virus (CTV) on Citrus paradisi (Macfad.) cv. “Marsh” in South Africa

Citrus tristeza virus (CTV) is endemic throughout the citrus production areas of South Africa and mild-strain cross-protection is employed to combat the negative effects of severe-strain infections. The country is among the world’s leading producers of grapefruit, however cross-protected trees often display severe stem grooving, regardless of the rootstock. Previously, cross-protection sources were evaluated empirically, through graft inoculations onto indicator hosts. Recent research has shown that cross-protection, possibly mediated by super-infection exclusion, is strain-specific. This, coupled with the varying affinities that cultivars display for different CTV strains, has shown the need to determine which CTV strains are associated with specific commercial cultivars. In this study, thirty-six Citrus paradisi (Macfad.) cv. “Marsh” plants were sampled in the South African grapefruit production areas of Malelane and Pongola. CTV populations from these samples were analysed through the amplification of the p33 gene and subsequent direct Sanger sequencing. A subset of 12 of these amplicons was selected for deep Illumina MiSeq sequencing. The resulting data showed high intra- and inter- orchard diversity of CTV, with populations showing similar genotype compositions to those found in recent studies on the “Star Ruby” cultivar. Populations were composed of a clearly dominant component, in most cases RB or Kpg3/SP/T3-like sequences, with at least two minor sequence types. AT-1-like and VT-like sequences were found to be dominant in only four and one of the analysed populations respectively. HA16–5, Taiwan-Pum/M/T5, T30 and B165 were present as intermittent minor components (less than 10% of mapped reads) across the populations.

Survey of Citrus tristeza virus (CTV) diversity in pigmented Citrus x paradisi (Macfad.) (Grapefruit) trees in north-western Argentina

Citrus tristeza virus (CTV) is the most severe viral pathogen of citrus and elicits a wide range of devastating disease symptoms. Grapefruit cultivars (Citrus x paradisi) are the most sensitive among citrus to the effects of CTV infections. Grapefruit is an important crop within the north-western Argentine citrus industry; however, production has been affected by CTV stem-pitting. In general, CTV diversity within South America is poorly studied, with data on grapefruit CTV populations being particularly limited. In this study, 50 samples were collected from Star Ruby, Henninger’s Ruby and Ruben Pink cultivars, within the provinces of Tucuman, Salta and Jujuy in north-western Argentina. The CTV p33 gene was PCR amplified and the resulting amplicons sequenced with Sanger sequencing. A subset of these amplicons was sequenced with Illumina MiSeq sequencing. AT-1-like sequences were dominant within the majority of populations, as determined by Sanger sequencing, followed by sequences clustering within the unresolved Kpg3/SP/T3 and RB clades. Sequencing by Illumina MiSeq confirmed this, as well as detecting minor sequence types within the HA 16–5, VT, B165 and A18 clades.

Phytochemical content and antioxidant activity of grapefruit (Star Ruby): A comparison between fresh freeze-dried fruits and different powder formulations

Different grapefruit powders obtained by freeze drying and spray drying with prior addition of shell materials (arabic gum and bamboo fiber) were studied in order to evaluate the effect of these preservation processes on the retention of antioxidants, in comparison with the freeze-dried fruit with no carriers added. Freeze-dried samples showed above 90% retention of these phytochemicals, while spray-dried samples presented good retention of vitamins but a sharp decrease in of phenolic compounds. Pearson's correlation analysis showed that the most significant contribution to DPPH scavenging activity and inhibition of β-carotene bleaching was provided by phenolic compounds, mostly flavonoids, while the contribution to the reducing power was due to ascorbic acid and α-tocopherol. Therefore, the loss of these compounds in the spray-dried samples resulted in products with lower antioxidant activity. Naringin and narirutin were the major phenolic compounds in all grapefruit samples, although other flavanones present in lower concentration, like hesperidin, neohesperidin didymin, poncirin or melitidin, also showed high correlations with the antioxidant value of the samples.

Effect of Citrashine Coating on Post Harvest Quality of Grapefruit Cv. Star Ruby under Ambient Conditions

Effect of Citrashine Coating on Post Harvest Quality of Grapefruit <i>Cv.</i> Star Ruby under Ambient Conditions

Effects of nine rootstocks on fruit yield and photosynthesis of ‘Star Ruby’ grapefruit

Net photosynthesis (PN), transpiration rate (E), stomatal conductance (gS), intercellular CO2 concentration (Ci), chlorophyll concentration (SPAD readings), chlorophyll fluorescence (Fv'/Fm') and yield (kg tree-1) of 'Star Ruby' grapefruit (Citrus paradisi Macfadyen) trees on nine rootstocks, sour orange (Citrus aurantium L.), 'Taiwanica' (Citrus taiwanica Tan. and Shim.), 'Yuzu' (Citrus junos Sieb. ex Tan.), 'Troyer' and 'Carrizo' citranges (Citrus sinensis Osb. × Poncirus trifoliata Raf.), 'Cleopatra' mandarin (Citrus reshni Hort. ex Tan.), 'Hyokan' (Citrus ampullacea Hort. ex Tan.), 'Kinkoji' (Citrus obovoidea Takahashi) and 'Sanbokan' (Citrus sulcata Takahashi) were compared under field conditions. Rootstocks affected the scion leaf chlorophyll concentration and PN. Leaf of trees on 'Carrizo' and 'Troyer' citranges had lower PN and chlorophyll concentration than those on the other rootstocks significantly. Scion on 'Cleopatra' mandarin, 'Taiwanica', sour orange, 'Sanbokan' and 'Hyokan' had higher cumulative yield whereas the lowest occurred on 'Carrizo' and 'Troyer' citranges.

Diversity of Citrus tristeza virus populations in commercial grapefruit orchards in Southern Africa, determined using Illumina MiSeq technology

Grapefruit cultivars are highly sensitive to CTV infections and in order to increase their productive lifespan, the Southern African citrus industry makes use of cross-protection. However, the breakdown of cross-protection is commonly observed in commercial grapefruit plantings. In order to determine which genotypes of CTV are associated with commercial Citrus x paradisi (Macfad.) cv. ‘Star Ruby’ in Southern Africa, 192 samples, pre-immunised with the GFMS 12 population, were collected from the grapefruit production areas of Hoedspruit, Malelane, Swaziland, Northern Cape, Sundays River Valley and Nkwalini Valley and six samples from non-pre-immunised plants in Letsitele as well as three samples from greenhouse maintained plants harbouring populations derived from the original GFMS 12 source. The p33 gene was amplified with direct Sanger sequencing performed on the resulting amplicons. A subset of 92 samples randomly selected and p33 gene amplicons subjected to Illumina MiSeq amplicon sequencing. High levels of CTV diversity were observed between and within orchards. Most populations were made up of a dominant component with several minor sequence types. Resistance Breaking (RB) sequences were most numerous, especially in recently planted orchards and present within all of the populations. The Kpg3/SP/T3 group appeared to be the second most prevalent, with increased prevalence in older orchards. Sequences mapping to HA 16–5, VT, AT-1, T36, Taiwan-Pum/M/T5 and T30, were represented sporadically within numerous collection sites.

Application of Vis/NIR spectroscopy for predicting sweetness and flavour parameters of ‘Valencia’ orange (Citrus sinensis) and ‘Star Ruby’ grapefruit (Citrus x paradisi Macfad)

Sweetness and flavour are desirable attributes used for quality control and assurance of citrus fruit, which are largely determined by total soluble solids (TSS), titrable acidity (TA) and TSS: TA ratio. However, the accuracies of TSS, TA and TSS: TA as flavour indices have been recently criticised. BrimA (Brix minus acids), on the other hand, is an accurate organoleptic parameter that has been shown to be highly related to sweetness and flavour of citrus fruit. In this study, the ability of visible to near infrared spectroscopy (Vis/NIRS), in reflectance mode, to non-destructively quantify BrimA, TSS, TA and TSS: TA ratio of ‘Valencia’ orange and ‘Star Ruby’ grapefruit was evaluated. Vis/NIR spectral data was acquired using a laboratory bench-top monochromator NIR Systems. Reference measurements and spectral datasets were subjected to partial least square (PLS) regression analysis. The best prediction models were observed for BrimA of ‘Valencia’ oranges with the coefficient of determination (R2) = 0.958; root mean square error of prediction (RMSEP) = 0.006 and residual predictive deviation (RPD) = 3.96, followed by TSS: TA ratio (R2 = 0.958; RMSEP = 0.605; RPD = 4.92). Good models for predicting flavor of grapefruit were also attained, with TSS having the best model (R2 = 0.896, RMSEP = 0.308 and RPD = 2.94), followed by BrimA (R2 = 0.858; RMSEP = 0.429; RPD = 2.45). These results demonstrated the ability of Vis/NIRS to non-destructively predict sweetness and flavour attributes of oranges and grapefruit. Vis/NIRS was recommended as a possible fast and accurate technique to be used for fruit discrimination based on flavour parameters during packing and for pricing of fruit in the market.

Characterization of Citrus tristeza virus Single-Variant Sources in Grapefruit in Greenhouse and Field Trials.

Citrus tristeza virus (CTV) is endemic to southern Africa and the stem pitting syndrome that it causes was a limiting factor in grapefruit production prior to the introduction of cross-protection in the Citrus Improvement Scheme. This disease mitigation strategy, using various field-derived CTV sources, has significantly extended the productive lifespan of grapefruit orchards in South Africa. CTV commonly occurs as a population of various strains, masking the phenotypic effect of individual strains. Likewise, current South African CTV cross-protection sources are strain mixtures, obscuring an understanding of which strains are influencing cross-protection. The severity of various CTV strains has mostly been assessed on sensitive indicator hosts, but their effect on commercial varieties has seldom been investigated. Single-variant CTV isolates were used to investigate the phenotypic expression of CTV strains in commercial grapefruit varieties as well as CTV indicator hosts. They were biologically characterized for their ability to cause stem pitting and their rate of translocation and titer in the different hosts, monitored by enzyme-linked immunosorbent assay. Complete genome sequences for three CTV strain variants were generated. Isolates of CTV strains VT, T68, RB, and HA16-5 did not induce severe stem pitting in four grapefruit hosts in a glasshouse trial. Viral titers of the strains differed in the grapefruit hosts, but the RB isolate reached a higher titer in the grapefruit hosts compared with the VT, T68, and HA16-5 isolates. Additionally, horticultural assessment of two grapefruit varieties inoculated with the RB isolate in two field trials demonstrated that mild stem pitting did not negatively influence the horticultural performance of the grapefruit trees over an eight-year assessment period. 'Star Ruby' trees containing the CTV source GFMS35 showed less stem pitting than trees inoculated with the RB isolate, but had smaller canopy volumes and lower yields than trees containing the RB isolate. This suggests that the influence of CTV sources on tree performance is not limited to the effect of stem pitting.

Seasonal variation in leaf nutrient concentration of grapefruit

Leaf samples of ‘Star Ruby’ grapefruit (Citrus paradisi Macf.) were collected from fruiting terminals (FT) and non-fruiting terminals (NFT) at monthly interval during the growing period to study the nutrient dynamics. The mean nutrient concentrations for N, P, K, Zn, Cu and Mn were found higher in the leaves from non-fruiting terminals (2.21%, 0.13%, 2.07%, 20.81 ppm, 10.68 ppm, 17.06 ppm) as compared to fruiting terminals (1.60%, 0.12%, 2.01%, 18.87 ppm, 9.92 ppm, 15.88 ppm). However, the mean nutrient concentrations for Ca, Mg and Fe were recorded higher in the leaves from fruiting terminals (4.10%, 0.412%, 145.50 ppm) as compared to nonfruiting terminals (3.94%, 0.367, 141.51 ppm). Similarly, K, Mg, Zn and Cu contents were higher in younger leaves, while, Ca, Fe and Mn contents were more in older leaves. There were non-significant variations in the content of N, P, K, Ca, Mg, Fe, Zn, Cu and Mn in the leaves from FT and NFT during September-October. The dynamics of leaves micronutrient content showed higher intensity of seasonal variations than the macronutrient content. The regression analysis explained the correlation between type of terminals and the linear regression in leaves accounted 86, 75 and 79% variability in data for the N, K and Mn, respectively.

Nitrogen source and nitrification inhibitors affect soil nutrient status and Star Ruby grapefruit performance

Nitrogen source and nitrification inhibitors affect soil nutrient status and Star Ruby grapefruit performance

Effect of Plant Growth Regulators and Fungicides on Huanglongbing-related Preharvest Fruit Drop of Citrus

The severe citrus (Citrus sp.) disease Huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus, has resulted in widespread tree decline in Florida and overall citrus production is now the lowest it has been in 50 years. More than 80% of Florida citrus trees are HLB affected, and most growers attempt to sustain production on infected trees through good asian citrus psyllid (Diaphorina citri) control and enhanced fertilization and irrigation management. Although production appears to benefit from these treatments, preharvest fruit drop is considerably greater than on uninfected trees. U.S. Department of Agriculture (USDA) data indicate that Florida statewide fruit drop has increased by 10% to 20% of the entire crop in the last three growing seasons, essentially doubling the historical levels. Extensive research is underway to identify solutions to HLB, but it is essential to maintain production on existing trees to sustain the industry in the near term. For decades, several plant growth regulators (PGRs) have been labeled to reduce preharvest fruit drop in commercial citrus. Trials of these materials, other nonlabeled PGRs, and some fungicides were conducted in two seasons to determine if fruit drop could be reduced. Randomized complete block design experiments were established using four to six replications of four- to six-tree groups as experimental units, blocked spatially. In 2013–14, sprays of gibberellic acid (GA), 2,4-dichlorophenoxyacetic acid (2,4-D), 1-naphthaleneacetic acid (NAA), S-abscisic acid (S-ABA), aminoethoxyvinylglycine (AVG), and 1-methylcyclopropene (1-MCP) were applied once or twice alone or in some combinations at standard rates to trees in various mature blocks of ‘Valencia’ and ‘Pineapple’ sweet orange (Citrus sinensis), ‘Star Ruby’ grapefruit (Citrus paradisi), or ‘Murcott’ tangor (Citrus reticulata ×C. sinensis) in central Florida in the Indian River area. Only 1 of the 10 individual trials had treatments with significantly lower drop rates than controls; and when pooled across all experiments, GA + 2,4-D reduced number of fruit dropped per tree 4%, but only at P = 0.10. NAA, S-ABA, AVG, and 1-MCP had no effect and were not used the following year. Starting in 2014, treatments were initiated earlier in the season with greater effort to minimize variability: GA; 2,4-D; GA + 2,4-D; a natural GA, indolebutyric acid, cytokinin mix; and strobilurin fungicides were applied to 22 mature blocks of ‘Hamlin’ and ‘Valencia’ sweet orange trees. In 2014–15, only three of the 11 individual ‘Hamlin’ trials and one of the 11 ‘Valencia’ trials included a treatment with significant drop reduction compared with controls. However, when all the tests on ‘Hamlin’ were pooled, there was a significant 5% reduction in total crop drop for GA + 2,4-D and significant reductions with many of these PGRs alone, but in only one case with fungicide treatments. When all tests on ‘Valencia’ were combined, 2,4-D reduced drop significantly but only by 2% of the total crop (14% drop vs. 16% drop), but fruit drop in ‘Valencia’ blocks was near the historical average in control trees. Soil conditions and tree conditions were similar across all test sites and there were no apparent relationships between product efficacy and observed tree condition or any other grove characteristics. In addition, four ‘Hamlin’ and four ‘Valencia’ blocks were treated with 1/4 rates of 2,4-D + 6-benzyladenine every 45 days during the growing season (six sprays) and three of the eight individual trials showed significant reductions in drop: when pooled, these treatments reduced drop by 3% in ‘Valencia’ and 6% in ‘Hamlin’. At this time, PGRs cannot be recommended as a consistent way to reduce fruit drop related to HLB, but further work needs to be conducted to refine the most promising treatments.

Implication of the antioxidant system in chilling injury tolerance in the red peel of grapefruit

Previous observations have indicated that the red peel areas of grapefruit with high lycopene concentrations were more tolerant to CI than yellow peel areas (Lado et al., 2015a). Because lycopene is a carotene with powerful antioxidant capacity, this study investigated whether the CI tolerance of the lycopene-accumulating rind of grapefruit may be due to an enhancement of the enzymatic and/or non-enzymatic antioxidant systems. Total antioxidant capacity, antioxidant metabolite (GSH and AsA) contents, and antioxidant enzyme (GR [glutathione reductase], ascorbate peroxidase [APX], catalase [CAT] and superoxide dismutase [SOD]) activity and gene expression were measured in the peel of Star Ruby grapefruit with contrasting CI tolerance during storage at 2°C for up to 58d. The peel of CI-tolerant fruit exhibited a lower lipid peroxidation level (MDA content). The hydrogen peroxide concentration was similar after 3 weeks of storage, when the differences in chilling damage between sensitive and tolerant fruit were noticeable, suggesting that the increase in H2O2 is a response of flavedo cells to cold stress that is not necessarily related to the development of CI. Moreover, CI tolerance was not associated with enhancement of either total antioxidant capacity or glutathione and AsA contents, indicating that such antioxidant responses may be cold-mediated and not directly linked to chilling tolerance. Analysis of singlet oxygen scavenging capacity by the SOAC assay revealed considerably higher activity in the lycopene-accumulating peel than in the yellow peel at harvest time and throughout the entire cold storage and shelf-life period. Enzymatic activity and gene expression analyses of GR, APX and SOD did not reveal the involvement of these antioxidant enzymes in the protection against CI. However, high CAT activity was detected in the peel of CI-tolerant fruit, although this difference did not correlate with changes in the expression levels of the CAT1 and CAT2 genes. Therefore, the boost in singlet oxygen scavenging capacity is likely the primary factor responsible for CI tolerance in the lycopene-accumulating peel of grapefruit.

&lt;b&gt;The influence of rootstock and time of harvest on the fruit quality during storage of in two grapefruit cultivars

The effects of the ‘Cleopatra’ mandarin and ‘Swingle’ citrumelo rootstocks and time of harvest on the quality of cold-stored (13°C and 90% R.H.) ‘Ruby Red’ and ‘Star Ruby’ grapefruit grown under the tropical conditions prevalent in Ceará state, Brazil, were evaluated. Fruit quality was assessed by mass loss and peel color, the percentage of juice, soluble solids, titratable acidity, pH, maturity index, and ascorbic acid content. The results suggested that ‘Ruby Red’ and ‘Star Ruby’ grapefruit presented similar amounts of soluble solids, pH, titratable acidity and ascorbic acid levels at harvest, and the trends over the course of storage followed similar patterns for both cultivars, regardless of rootstock. The influence of scion-rootstock combination on the studied variables was dependent on the time of harvest. The peel color of ‘Ruby Red’ grafted on ‘Swingle’ citrumelo is more vivid and redder when harvested in October than when harvested in August. ‘Ruby Red’ and ‘Star Ruby’ grapefruit harvested in October are sweeter, less acidic, juicier, and richer in ascorbic acid than those harvested in August. ‘Cleopatra’ mandarin rootstock might favor ascorbic acid levels at harvest, but the fruit may lose more weight during storage.

Exploring the diversity in Citrus fruit colouration to decipher the relationship between plastid ultrastructure and carotenoid composition

Differentiation of new and characteristic plastid ultrastructures during ripening of citrus fruits in both peel and pulp appears to be strongly correlated with the content and complement of carotenoids. Most of the species of the Citrus genus display a wide range in fruit colouration due to differences in carotenoids; however, how this diversity is related and may contribute to plastid differentiation and ultrastructure is currently unknown. To that end, carotenoid profile and plastid ultrastructure were compared in peel and pulp of three sweet oranges: the ordinary orange-coloured Navel, rich in β,β-xanthophylls, the yellow Pinalate mutant with an elevated content of colourless carotenes and reduced β,β-xanthophylls, and the red-fleshed Cara Cara with high concentration of colourless carotenes and lycopene in the pulp; and two grapefruits: the white Marsh, with low carotenoid content, and the red Star Ruby, accumulating upstream carotenes and lycopene. The most remarkable differences in plastid ultrastructure among varieties were detected in the pulp at full colour, coinciding with major differences in carotenoid composition. Accumulation of lycopene in Cara Cara and Star Ruby pulp was associated with the presence of needle-like crystals in the plastids, while high content of upstream carotenes in Pinalate pulp was related to the development of a novel plastid type with numerous even and round vesicles. The presence of plastoglobuli was linked to phytoene and xanthophyll accumulation, suggesting these structures as the main sites for the accumulation of these pigments. Peel chromoplasts were richer in membranes compared to pulp chromoplasts, reflecting their different biogenesis. In summary, differences in carotenoid composition and accumulation of unusual carotenoids are mirrored by the development of diverse and novel chromoplast types, revealing the plasticity of these organelles to rearrange carotenoids inside different structures to allow massive accumulation and thus contributing to the chemical stability of the carotenoids.

Response of young ‘Star Ruby’ grapefruit trees to regulated deficit irrigation with saline reclaimed water

In this study, the physiological and agronomic effects of irrigating a commercial young grapefruit orchard with saline reclaimed water (RW) combined or not with a regulated deficit irrigation (RDI) strategy were analyzed over three consecutive years. Two water sources, transferred water (TW; ECw≈1.3dSm−1) and reclaimed water (RW; ECw≈3.0dSm−1) were used, and two irrigation treatments, a control treatment (irrigated 100% of the crop evapotranspiration; ETc) and a RDI treatment (irrigated 50% of ETc during the 2nd stage of fruit growth) were performed. Results evidenced that RW, especially under the RDI strategy, increased the soil salinity, particularly in summer due to a greater evapotranspirative water demand. However, soil salinity did not increase, as salts were likely to be washed by rainfall. Stomatal conductance and net photosynthesis were not affected by the use RW combined or not with RDI strategies. However, RDI strategies worsened the tree water status regardless of the type of water used; TW or RW, although re-watering increased rapidly the stem water potential up to values similar to that of the control trees. The RDI treatment, which allowed reaching an average annual water saving of 13.2%, combined or not with RW, did not negatively affect vegetative growth, yield and fruit quality, which might be of great economic and competitive significance for agriculture. The combination of RW and RDI did have not affect negatively the soil and young grapefruits, but further research focused on a longer term should be carried out since detrimental effects might appear.

First Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in Turkey

HomePlant DiseaseVol. 99, No. 4First Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in Turkey PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fusarium Root Rot Caused by Fusarium oxysporum Infecting Pigmented Grapefruit Trees in TurkeyF. Baysal-Gurel and A. CinarF. Baysal-GurelSearch for more papers by this author and A. CinarSearch for more papers by this authorAffiliationsAuthors and Affiliations F. Baysal-Gurel , Department of Plant Pathology, The Ohio State University, OARDC, Wooster 44691 A. Cinar , Department of Plant Protection, Faculty of Agriculture, Cukurova University, Balcali, Adana, Turkey 01330. Published Online:1 Apr 2015https://doi.org/10.1094/PDIS-07-14-0746-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Pigmented grapefruit trees (Citrus paradisi Macf. cvs. Star ruby and Rio red) grafted on sour orange (Citrus aurantium L.) exhibiting root rot symptoms have been observed in three orchards in Adana, Turkey, since 1996. Symptoms were decay of roots and aboveground parts (below the grafting point) without oozing gum and vascular discoloration. Infected trees showed reduced vigor and chlorosis on the foliage. The disease incidence was nearly 5 to 10% in each orchard. Nine diseased root parts from nine different plants were surface-sterilized with 1% NaClO for 2 min and cultured on Fusarium-selective medium (3) at 25°C for 1 week. The culture was transferred to potato dextrose agar (PDA) to determine cultural characteristics. Nine isolates consistently yielded white to purple aerial hyphae and produced abundant oval to ellipsoidal, unicellular microconidia (2.2 to 4.1 × 4.3 to 11.0 μm) borne in false heads on short monophialidic conidiophores, three-to-five-septate macroconidia with pedicellate bases (2.2 to 5.7 × 18.7 to 42.8 μm), and chlamydospores (2). To confirm pathogen identity, total DNA was extracted directly from fungal mycelium, using the PowerSoil DNA isolation kit (MO BIO Laboratories, Inc., Carlsbad, CA). The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (4) and sequenced. The sequence, deposited in GenBank (Accerssion No. KP119604), was 99% identical to that of Fusarium oxysporum isolates from Spain (KC427029) and China (JN232163). Morphological and cultural characteristics and PCR confirmed the identity of the causal agent as F. oxysporum Schlechtend.:Fr. Ten 14-month-old Star ruby and Rio red plants, grafted on sour orange and transplanted into steam-sterilized potting mix, were drench-inoculated with a conidial suspension (1 × 106 conidia/ml and 50 ml/plant) of a selected isolate (CU2-97) harvested from a 7-day-old culture on PDA. Plants were maintained in a greenhouse from a low of 20°C at night to a high of 25°C during the day until symptoms appeared. Ten control plants from each pigmented grapefruit were drenched with sterilized water and maintained in the same greenhouse. Three months after inoculation, roots and aboveground parts below the grafting point of the grapefruit plants developed necrotic areas on all inoculated seedlings, and fungus was re-isolated from root parts. All control plants remained disease-free, and no fungus was re-isolated. F. oxysporum was reported infecting sweet orange and tangerines grafted on sour orange in Tunisia in 2014 (1). To our knowledge, this is the first report of Fusarium root rot caused by F. oxysporum infecting pigmented Star ruby and Rio red grapefruit grafted on sour orange in Turkey. This indicates that grapefruit trees grafted on sour orange could be at risk for infection of this potentially destructive disease in Turkey.