An Update of the Crop Management Practices Enhancing Yield and Quality in Citrus

A special issue of Horticulturae (ISSN 2311-7524). This special issue belongs to the section "Fruit Production Systems".

Deadline for manuscript submissions: 20 June 2024 | Viewed by 8594

Special Issue Editor


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Guest Editor
New South Wales Department of Primary Industries, Silver City Highway, Dareton 2717, Australia
Interests: rootstock/variety evaluation; plant growth regulators; crop management; flowering physiology; stress physiology; heat unit/chill unit mapping; climate change; citrus; persimmons
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Special Issue Information

Dear Colleagues,

Citrus and its close relatives are in the subfamily Aurantioideae of the very diverse family Rutaceae.  The citrus tribe of interest to us is Citreae, and the subtribe Citrinae contains the citrus fruit trees. The principal species of the genus Citrus include sweet orange (Citrus sinensis), mandarin (Citrus reticulata), grapefruit (Citrus paradise), lemon (Citrus limon), lime (Citrus aurantifolia), pumelo (Citrus grandis). Some of these species comprise many cultivated varieties (cultivars) which generally differ in fruit size, shape, seed content, quality and season of maturity more than they vary in cultural requirements.

Citrus is grown throughout the world in most areas where mean temperatures stay above 13 oC. In general, the commercial citrus-producing countries lie between 40- degree north and 40-degree south latitudes. Many factors influence the world distribution of citrus, including soil and climatic factors. However, it is the minimum temperature which inevitably determines where citrus can be profitably grown.

Citrus is a long-lived perennial evergreen tree which can economically produce fruit for up to 50 years, and sometimes longer. Rootstock’s selection is the key to the success of any fruit tree, in terms of compatibility with scion wood, tree growth and the diversion of water and nutrients uptake from the soil. Different rootstocks suit different soil types.  Most of the world citrus is grown in deep sand, loam soil, or clay-type soil conditions.  It is important that the soil is well drained and that a proper nutrition program is scheduled throughout the growing season. The scion varieties play an important role in determining the market based on consumer preference. Consumers normally prefer sweet, easy-to-peel and juicy mandarin, with strong skin colour. The different varieties of sweet oranges also suit different consumers, and it depends on the time to maturity of different varieties. Due to the constant selection of sweet orange and mandarin varieties, the citrus growing season can last up to 8 or more months in many countries in northern and southern hemispheres.  Crop management practices to grow good quality fruit with a large marketable size have been very important.  Large-sized fruit return better profits for the growers compared to the small-sized fruit. Some of the citrus varieties are heavy bearers, especially mandarins, and therefore, proper fruit thinning practices must be carried out to reduce the crop load and enhance fruit size.  This practice also prevents the trees moving into biennial bearing patterns. Other crop management practices, such as pruning, must also be carried out after harvest to remove weak branches, and to produce strong shoots, which, in turn, bear good quality, large flowers.  Tree pruning also maintains tree size, and it makes it easy for the fruit pickers to pick fruit without ladders. Dwarfing rootstocks can offer tree size control and trees can be planted at much higher densities.

Dr. Tahir Khurshid
Guest Editor

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Keywords

  • rootstocks
  • dwarfing rootstocks
  • slat tolerance
  • varieties
  • crop phenology
  • fruit thinning
  • irrigation
  • citrus diseases
  • citrus fruit safety
  • climate change
  • oranges
  • mandarin

Published Papers (5 papers)

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Research

15 pages, 6098 KiB  
Article
Comparison of Citrus Leaf Water Content Estimations Based on the Continuous Wavelet Transform and Fractional Derivative Methods
by Shiqing Dou, Wenjie Zhang, Yuanxiang Deng, Chenhong Zhang, Zhengmin Mei, Jichi Yan and Minglan Li
Horticulturae 2024, 10(2), 177; https://doi.org/10.3390/horticulturae10020177 - 16 Feb 2024
Viewed by 704
Abstract
Citrus tangerines are famous fruits worldwide, and monitoring the water content of citrus leaves is highly important for citrus production. However, there are still challenges in quantitatively estimating the water content of citrus leaves using hyperspectral technology, and the random noise generated during [...] Read more.
Citrus tangerines are famous fruits worldwide, and monitoring the water content of citrus leaves is highly important for citrus production. However, there are still challenges in quantitatively estimating the water content of citrus leaves using hyperspectral technology, and the random noise generated during spectral acquisition and the overlapping peaks in the sensitive band of the citrus leaf water content will affect estimation accuracy. To solve these problems and further explore the roles of the continuous wavelet transform (CWT) and fractional-order derivative (FOD) in the estimation of citrus leaf water content, this study intends to use of CWT and FOD to decompose the original spectrum, and then compare the correlation between the original spectrum and leaf water content to explore whether the decomposition treatment has improved the correlation between spectrum and leaf moisture content. Then, the successive projections algorithm (SPA) was used to select feature bands and combine spectral vegetation indices. Partial least squares regression (PLSR) was used to construct water-content inversion models for citrus leaves, and the inversion accuracies of two commonly used spectral preprocessing methods were compared. The results indicate that (1) the CWT can improve the sensitivity of the spectrum to the citrus leaf water content to a certain extent, and the inversion accuracy of the CWT is approximately 5% greater than that of the FOD. (2) On the basis of the CWT and FOD methods, the inversion accuracy of the citrus leaf water content based on SPA screening increased by 9.61% and 9.29%, respectively, compared with the original spectrum. (3) Under CWT decomposition, Scale4 of the Gaus1 wavelet was screened by the SPA, and the inversion model of citrus leaf water content was constructed by combining the spectral vegetation index NDVI with the best results. The R-squared (R2) and root mean square error (RMSE) values were 0.7491 and 0.0284, respectively, which were both 0.0138 greater than those of the best inversion model for the FOD R2. In conclusion, the CWT-SPA combined with the spectral vegetation index can improve the sensitivity of the spectrum to the citrus leaf water content, eliminate a large amount of redundant data, and enhance the prediction ability and stability of the citrus leaf water content. Full article
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12 pages, 507 KiB  
Article
The Use of Cubic Smoothing Spline Models for Predicting Early Fruit Size in ‘Keenan’ Valencia (Citrus sinensis L. Osbeck) Oranges
by Tahir Khurshid, Ben Braysher and Jane Elizabeth Khurshid
Horticulturae 2024, 10(2), 149; https://doi.org/10.3390/horticulturae10020149 - 5 Feb 2024
Viewed by 770
Abstract
Fruit size is an important factor for the sale of fruit in fresh markets. Fruit size prediction early in the growing season would help with planning harvest operations, administering marketing strategies and an advance determination of the proportion of fruit that will be [...] Read more.
Fruit size is an important factor for the sale of fruit in fresh markets. Fruit size prediction early in the growing season would help with planning harvest operations, administering marketing strategies and an advance determination of the proportion of fruit that will be suitable for certain size classes. Fruit diameter growth of ‘Keenan’ Valencia oranges was measured over five consecutive growing seasons (2014–2018) during Stage II (cell enlargement) and Stage III (maturation) periods between January and October. Fruits were randomly selected and tagged from around the tree canopy to record the fruit diameter at fortnightly intervals until harvest. The data were used to develop a fruit size prediction model using the cubic smoothing splines technique. Results indicated that from the fruit growth patterns, an accurate prediction of the final fruit size and distribution were possible during the early Stage II fruit development phase, 6–7 months ahead of the final harvest. It was concluded that fruit size must be 66 mm in diameter by 30 March to attain a fruit size > 77 mm at harvest. This model was tested in 2019 with an accuracy of 97% in predicting fruit size distribution harvest across three size classes. Full article
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16 pages, 2080 KiB  
Article
Response to Deficit Irrigation of ‘Orogrande’ Mandarin Grafted onto Different Citrus Rootstocks in Spain
by Amparo Primo-Capella, María Dolores Molina-Nadal, Laura Catalá-Senent, Agustí de Miguel-Moreno, María Ángeles Forner-Giner and Mary-Rus Martínez-Cuenca
Horticulturae 2024, 10(1), 37; https://doi.org/10.3390/horticulturae10010037 - 29 Dec 2023
Viewed by 917
Abstract
Drought is increasingly becoming an abiotic stress factor that affects citrus yield in the Mediterranean Basin, and rootstocks may impact the plants’ responses to it. This study compares the influences of Forner-Alcaide 5 (FA-5), an emerging well-established rootstock in Spain, and Carrizo citrange [...] Read more.
Drought is increasingly becoming an abiotic stress factor that affects citrus yield in the Mediterranean Basin, and rootstocks may impact the plants’ responses to it. This study compares the influences of Forner-Alcaide 5 (FA-5), an emerging well-established rootstock in Spain, and Carrizo citrange (CC), the common commercial rootstock of the Orogrande mandarin variety, on plants’ responses to water reduction. The deficit irrigation (DI) condition was established by 50% irrigation and evapotranspiration (ETc). The canopy volume, yield, fruit size and fruit internal quality were evaluated. The yield reduction in the CC DI was mainly due to a smaller fruit size, but in FA-5, it was due to fewer fruits without an affected caliber. Regarding Ct, the fruits from the CC DI had lower juice contents and higher rind percentages, while the differences between the Ct and DI trees were smaller in the FA-5 rootstock. The most remarkable effect was the increase in total soluble sugars (TSS) for the DI treatment. To conclude, the FA-5 rootstock had the strongest influence on Orogrande mandarin under water stress. These results can be useful for addressing water stress problems in citrus. Full article
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17 pages, 2010 KiB  
Article
Physiological and Biochemical Adaptive Traits in Leaves of Four Citrus Species Grown in an Italian Charterhouse
by Maurizio Curadi, Ilaria Marchioni, Matteo Mancino, Luisa Pistelli, Laura Pistelli and Andrea Scartazza
Horticulturae 2022, 8(4), 324; https://doi.org/10.3390/horticulturae8040324 - 12 Apr 2022
Cited by 2 | Viewed by 1844
Abstract
Citrus trees are a very important crops that are cultivated worldwide, but not much knowledge is known about the ecophysiological responses to climatic changes in trees under natural conditions. The aim of this study was to investigate their adaptive capacity in response to [...] Read more.
Citrus trees are a very important crops that are cultivated worldwide, but not much knowledge is known about the ecophysiological responses to climatic changes in trees under natural conditions. The aim of this study was to investigate their adaptive capacity in response to seasonal phenological and environmental changes. The trial included Citrus trees (sweet orange, bitter orange, lemon, mandarin) growing under non-regular cropping conditions in a Monumental Charterhouse in Tuscany, in a subtropical Mediterranean climate with hot summer conditions. During a 1-year field trial, we determined the variations in chlorophyll fluorescence parameters and leaf biochemical traits (content of chlorophylls and carotenoids, total phenolic content (TPC), total antioxidant capacity (TAC), and total non-structural carbohydrates). In all Citrus spp., interspecific mean values of photochemical efficiency peaked during the summer, while a marked photoinhibition occurred in the winter in concomitance with higher interspecific mean values of leaf TPC, TAC, and non-structural carbohydrates. The trees showed the pivotal role played by photosynthetic acclimation as a survival strategy to tolerate abiotic stress in the climate change hotspot of Mediterranean environment. This study is included in a wider project aimed at a new valorization of Citrus trees as genetic resource and its by-products with added-value applications for innovative functional foods. Full article
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17 pages, 993 KiB  
Article
Correlation of Soil Characteristics and Citrus Leaf Nutrients Contents in Current Scenario of Layyah District
by Niaz Ahmad, Sajjad Hussain, Muhammad Arif Ali, Asif Minhas, Waqar Waheed, Subhan Danish, Shah Fahad, Umber Ghafoor, Khurram Shehzad Baig, Haider Sultan, Muhammad Iftikhar Hussain, Mohammad Javed Ansari, Theodore Danso Marfo and Rahul Datta
Horticulturae 2022, 8(1), 61; https://doi.org/10.3390/horticulturae8010061 - 10 Jan 2022
Cited by 17 | Viewed by 3517
Abstract
Soil with low fertility is a big problem for achieving citrus productivity. In this regard, the management of macro and micronutrients is essential. Macro and micronutrient deficiency decreased the yield and the quality of citrus fruit. It is the need of the hour [...] Read more.
Soil with low fertility is a big problem for achieving citrus productivity. In this regard, the management of macro and micronutrients is essential. Macro and micronutrient deficiency decreased the yield and the quality of citrus fruit. It is the need of the hour to classify the soil fertility status under changing climatic scenarios. The current soil fertility survey was conducted to examine the macro and micronutrient status in the citrus production area. In soil, three depths (0–15, 15–30, and 30–45 cm) were taken for sampling. For leaves, 4–6-months-old non-bearing twigs were sampled from 20 trees per orchard at breast height. Results showed that soil pH (7.1–8.4) was slightly alkaline, electrical conductivity (EC) was non-saline (<4 dSm−1), soil organic matter (SOM) was deficient (<0.86%), and calcium carbonate (CaCO3) was slight calcareous (<8%), at 0–15, 15–30, and 30–45 cm depths. The majority of soil samples were low in nitrogen (N) contents at all depths, i.e., (<0.043) 0–15 (85%), 15–30 (97%), and 30–45 (100%) cm depths. Phosphorus (P) was medium (7–15 mg kg−1) at 0–15 cm (60%) but low (<7 mg kg−1) at 15–30 (63%) and 30–45 cm (82%) depths. Potassium (K) was medium (80–180 mg kg−1) at 0–15 (69%), 15–30 (69%), and 30–45 cm (10%) depths. Boron (B) and manganese (Mn) were medium, and Cu was high in 0.15 cm, but all were low at 15–30 and 30–45 cm depths. Iron (Fe) and zinc (Zn) were low at depths of 0–15, 15–30, and 30–45 cm. Most citrus leaves were deficient in N (94%), Fe (76%), Zn (67%), and B (67%). In conclusion, soil fertilization is not sufficient for optimum citrus yield because of alkaline pH and slight calcareous soil conditions in this region. Foliar application of nutrients is suggested instead of only soil fertilization, for better nutrient management in citrus orchards. Full article
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