24 May 2024
Citrus flower

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

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

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

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

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

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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20 Mar 2024
The effect of avocado sunblotch disease

The effect of avocado sunblotch disease (ASBD) on tree morphology, fruit maturity, yield and quality of ‘Hass’ avocado in South Africa

Avocado sunblotch viroid (ASBVd) is found in many avocado-growing regions of the world, where it affects fruit yield and quality. The trees develop two types of infections: symptomatic and symptomless infections. Symptoms are most obvious as yellow streaks on leaves, fruit and green stems of symptomatic trees and symptomless carrier trees do not display any such symptoms. Symptomless carrier trees are considered the primary source of disease transmission in orchards. Hence, this study investigated the impact of ASBVd-infected symptomless carrier trees on tree morphology, fruit maturity, yield and quality of ‘Hass’ avocado from 2019 until 2021. Differences were observed in the orchard between infected and healthy trees; trees with medium and high viroid concentrations excessively produced flowers, lost leaves during flowering and ultimately bore few to no fruit at the end of the season.

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20 Mar 2024
Leaf Analysis

Leaf Analysis in Citrus: Recent Development

This article encompasses nutrient diagnosis through leaf analysis and leaf nutrient composition. The corresponding leaf nutrient values expressed in % were: N (2.23–2.49), P (0.10–0.11), K (1.86–2.12), Ca (2.12–2.32), Mg (0.28–0.38), and in ppm Fe (148.2–179.8), Mn (72.2–84.8), Cu (10.4–18.6), and Zn (24.2–38.8) representing eight states viz., West Bengal, Sikkim, Assam, Meghalaya, Tripura, Mizoram, Arunachal Pradesh, and Manipur. Nutrient constraints in the form of nitrogen, phosphorus, calcium, magnesium, copper and zinc through leaf nutrient diagnostics tools were diagnosed. It finds a due place in the region’s fertilizer program of mandarin orchards to obtain sustainable optimum fruit yield. While through leaf analysis in Manipur, DRIS indices revealed different nutrients to be ordered as zinc < phosphorus < calcium < magnesium < nitrogen < potassium < iron < manganese < copper.

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