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25 Jun 2024
Huanglongbing infected orange trees
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Identification of citrus greening based on visual symptoms: A grower’s diagnostic toolkit

Citrus greening is one of the world’s most serious diseases of citrus that affects all cultivars and causes the systematic death of trees worldwide. The disease is caused mostly by the bacteria Candidatus Liberibacter species. The wind, rain, and touch of infected workers cannot transmit this infectious disease. The Asian Citrus Psyllid (ACP), a minuscule insect, is one of the main vectors that transmit the disease by feeding on citrus leaves. Citrus greening management is also quite expensive since no successful treatment for the cure has been found, except to remove all affected vegetables from healthy crops to eliminate the bacterial spread.

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25 Jun 2024
Citrus Black Spot
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The Effects of Postharvest Treatments and Sunlight Exposure on the Reproductive Capability and Viability of Phyllosticta citricarpa in Citrus Black Spot Fruit Lesions

Citrus black spot (CBS) is caused by Phyllosticta citricarpa, which is classified as a quarantine organism in certain countries whose concerns are that CBS-infected fruit may be a pathway for introduction of the pathogen. This study evaluated the reproductive capability and viability of P. citricarpa under simulated conditions in which the whole fruit, peel segments, or citrus pulp with CBS lesions were discarded. Naturally infected ‘Midknight’ Valencia orange and ‘Eureka’ lemon fruit, either treated using standard postharvest sanitation, fungicide, and wax coating treatments or untreated, were placed into cold storage for 5 weeks (oranges at 4 °C and lemons at 7 °C). Thereafter, treated and untreated fruit were incubated for a further 2 weeks at conditions conducive for CBS symptom expression and formation of pycnidia. The ability of pycnidia to secrete viable pycnidiospores after whole fruit and peel segments or peel pieces from citrus pulp were exposed to sunlight at warm temperatures (±28 °C) and ±75% relative humidity levels was then investigated.

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24 May 2024
Citrus flower
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Demonstration of a Change in Nitrogen Metabolism Influencing Flower Initiation in Citrus

Changes in the leaf NH3-NH4 + content were monitored during floral induction in Citrus. Five-year-old rooted cuttings of ‘Washington’ navel orange (Citrus sinensis) were induced to flower by subjecting the trees to 8 weeks of low temperature, 8-h day (500 μE m−2 s−1) at 15–18°C/16-h night at 10–13°C and by transferring them afterwards to 12-h day (500 μE m−2 s−1) at 24°C/12-h night at 19°C. Maximum bloom occurred 4 weeks after the transfer to the warmer temperature. The number of flowers and the NH3–NH4 + content of leaves increased significantly (p < 0.05 and P < 0.01, respectively) with the length of the low temperature treatment. Sixteen-year-old ‘Frost Lisbon’ lemon trees (Citrus limon) on ‘Troyer’ citrange rootstocks (C. sinensis × Poncirus trifoliata) under commercial production were subjected to water-deficit stress of increasing severity.

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24 May 2024
Effect of different salinity levels
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Salinity Level Influenced Morpho-physiology and Nutrient Uptake of Young Citrus Rootstocks

Soil and irrigation water salinity are major limiting factor to citrus industry in arid environments. The objective of this study was to assess the effects of different salt stress levels on growth and ion uptake of three-month-old citrus rootstocks; sour orange (Citrus aurantium) and Volkamer lemon (Citrus volkameriana). Six levels of NaCl-salinity were used, 0.7 (control), 2, 4, 8, 12 and 15 dS m-1. Salinity increment from 2.0 to 15.0 dS m-1 significantly reduced seedlings height, stem diameter, leaf area, root dry weight, leaf relative water content, chlorophyll content index and chlorophyll fluorescence by one to three folds. In addition, leaf and root N concentration reduced by 10%–50%, P 6%–50%, K 8%–47%, Ca+2 7%–51% and Mg+2 7%–50% when salt stress in the irrigation water increased from 2.0 to 15.0 dS m-1.

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26 Apr 2024
Foster Grapefruit
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Effect of harvesting method on quality and storability of grapefruits

The effect of harvesting method on fruit quality and storability of the pink-fleshed ‘Foster’ grapefruits, at 18±1°C and 85%-90% r.h., was evaluated. The traditional method, using a hooked pole, was compared with an improved technique, where the picking pole was equipped with a long cloth sleeve held open by a ring for collecting the harvested fruits.

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26 Apr 2024
Pomelo
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Influence of Water Stress in Autumn on Flower Induction and Fruiting in Young Pomelo Trees

Young pomelo trees grown in concrete pots in a plastic house were water-stressed for different durations from early September to late December, 1990. The cyclical stress treatments were established by withholding water from the potted trees until the leaf water potentials reached -24 to -28 bars (7 to 13 days after irrigation) at which time they were re-irrigated. Maximum day and minimum night temperatures in the plastic house were adjusted to about 25° and 10°C, respectively, from early December, 1990, to early April of the following year.

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26 Apr 2024
Citrus Fruiting
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Effects of Water-deficit Stress and Gibberellic Acid on Floral Gene Expression and Floral Determinacy in ‘Washington’ Navel Orange

Effects of water-deficit stress and foliar-applied gibberellic acid (GA3) on ‘Washington’ navel orange (Citrus sinensis) floral gene expression and inflorescence number were quantified. Trees subjected to 8 weeks of water-deficit stress [average stem water potential (SWP) −2.86 MPa] followed by 3 weeks of re-irrigation (SWP recovered to > −1.00 MPa) produced more inflorescences in week 11 than trees well-irrigated (SWP > −1.00 MPa) for the full 11 weeks (P < 0.001). After 8 weeks of water-deficit stress, bud expression of flowering locus t (FT), suppressor of overexpression of constans1 (SOC1), leafy (LFY), apetala1 (AP1), apetala2 (AP2), sepallata1 (SEP1), pistillata (PI), and agamous (AG) increased during the re-irrigation period (weeks 9 and 10), but only AP1, AP2, SEP1, PI, and AG expression increased to levels significantly greater than that of well-irrigated trees.

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20 Mar 2024
Citrus Rind
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Biochemical bases and molecular regulation of pigmentation in the peel of Citrus fruit

External colour of Citrus fruits is one of the most important quality traits and a decisive factor for consumer acceptance. Pigmentation of fruit peel is highly diverse among the different species and cultivars of the genus Citrus, ranging from the green of limes to the yellow of lemons, orange in mandarins and sweet oranges, and pink in red grapefruits. Colouration of the peel is due to the presence of two main pigments: chlorophylls which provide green colour, and carotenoids, which are responsible for the characteristic colouration of mature fruits of most species and cultivars. Anthocyanins are a third group of pigments, providing a red to purple tint, in a specific group, blood oranges, and mainly restricted to the flesh. Chlorophylls and carotenoids are isoprenoid-derived pigments, synthesized and accumulated in plastids and, therefore, changes in these compounds during natural ripening are driven by the transformation of chloroplasts into chromoplasts. Most of the structural genes involved in chlorophylls and carotenoids metabolism have been characterized in Citrus, concluding that content and composition of these pigments are mostly genetically determined, and highly regulated at the transcriptional level.

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