15 Feb 2016

Fruit Splitting in Citrus

Paul J. R. Cronje
Citrus Research International | Department of Horticultural Science, Stellenbosch University

Ockert P. J. Stander and Karen I. Theron
Department of Horticultural Science, Stellenbosch University

Various citrus cultivars of ‘Navel’ and ‘Valencia’ orange [Citrus sinensis (L.) Osbeck], as well as mandarin and mandarin hybrids (Citrus reticulata Blanco) are prone to a preharvest physiological rind disorder, known as fruit splitting.

Similar disorders occur as fruit cracking and/or splitting in other commercially important horticultural crops, most notably in apple, apricot, cherry, grape, nectarine, prune, and tomato. Fruit splitting in citrus differs from other crops due to the unique morphology of a citrus fruit, consisting of the pulp and rind, which is made up of the spongy white internal layer, the albedo (mesocarp), and the external layer, the flavedo (exocarp).

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15 Feb 2016

Postharvest rind breakdown of ‘Nules Clementine’ mandarin is influenced by ethylene application, storage temperature and storage duration

Paul J.R. Cronje and Graham H. Barry
Citrus Research International | Department of Horticultural Science, Stellenbosch University

Marius Huysamer
Department of Horticultural Science, Stellenbosch University

The progressive postharvest disorder of ‘Nules Clementine’ mandarin (Citrus reticulata Blanco), referred to as rind breakdown (RBD), starts to develop during storage, about 3–5 weeks after harvest. Variation within the tree canopy, i.e. inside or outside canopy positions, as well as postharvest handling practices such as ethylene degreening, storage temperature and storage duration, were investigated for their influence on RBD incidence. Two experiments were conducted wherein fruit were subjected, in the first experiment, to ethylene degreening and a delay in commencement of cold storage (2004), and, in the second experiment, fruit were sampled from the inside and outside of the canopy and cold-stored at either −0.5 ◦C or 7.5◦C during 2005 and 2007.

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15 Feb 2016

Canopy position affects pigment expression and accumulation of flavedo carbohydrates of ‘Nules Clementine’ Mandarin Fruit, thereby affecting rind condition

Paul J.R. Cronje and Graham H. Barry
Citrus Research International | Department of Horticultural Science, Stellenbosch University

Marius Huysamer
Department of Horticultural Science, Stellenbosch University

Because photosynthesis provides the required carbohydrates for fruit development and respiration releases the stored energy from these carbon compounds, interalia during postharvest storage, it is therefore important that fruit tissues have an adequate carbohydrate concentration at the start of the postharvest period to ensure optimal storage life. In addition to photosynthate supply from leaves, the chlorophyll-containing flavedo of citrus (Citrus sp.) fruit (outer, colored part of the rind) has the ability to fix CO2 through its own photosynthetic system.

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15 Feb 2016

Spray application in citrus – Sprayer calibration and checklist

Gideon van Zyl, Paul Fourie, Tian Schutte, Tim Grout (CRI) and Johan van Zyl (Nexusag)
CRI Cutting Edge, Research News from Citrus Research International

Fungicides and pesticides are only as effective as their application. The main objective of spray application is the optimal dose transfer of the well agitated tank mix, which includes one or more active ingredients, from the sprayer to the tree, whilst keeping off-target losses from run-off and drift at a minimum.

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15 Feb 2016
Valencia Leaves

Assessment of retention and persistence of copper fungicides on orange fruit and leaves using fluorometry and copper residue analyses

Gerhardus C. Schutte and Charl Kotze
Citrus Research International

J. Gideon van Zyl and Paul H. Fourie
Department of Plant Pathology, Stellenbosch University

High volumes of copper hydroxide, cuprous oxide and copper oxychloride were sprayed under natural conditions onto mature orange trees to compare the etention on citrus leaves and fruit over a period of 56 days by means of copper residue analyses and a spray deposition assessment protocol using fluorometry, photomacrography and digital image analyses. Rainfall and increase in fruit size were also recorded to determine if it had an influence on weathering of copper residues.

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15 Feb 2016

Evaluation of two organosilicone adjuvants at reduced foliar spray volumes in South African citrus orchards of different canopy densities

J. Gideon van Zyl and Paul H. Fourie
Citrus Research International | Department of Plant Pathology, Stellenbosch University

Ewald G. Sieverding
Evonik Industries AG, Goldschmidtstraße, Germany

David J. Viljoen
Evonik Africa (Pty) Ltd, Somerset West

South African citrus fruit producers rely heavily on medium to high volume fungicide spray applications (Grout, 1997, 2003) to protect citrus fruit from challenging diseases such as Citrus black spot (CBS) (Phyllosticta citricarpa (McAlpine) van der Aa (syn. Guignardia citricarpa Kiely)) (Kotze, 1981, 2000; Schutte et al., 1997) and Alternaria brown spot (Alternaria alternata (Fr: Fr) Keissl., tangerine pathotype) (Schutte, 1996).

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15 Feb 2016

Spray deposition assessment and benchmarks for control of Alternaria brown spot on mandarin leaves with copper oxychloride

J. Gideon van Zyl and Paul H. Fourie
Citrus Research International | Department of Plant Pathology, Stellenbosch University

Gerhardus C. Schutte
Citrus Research International

Inadequate disease control on citrus foliage and fruit is often attributed to insufficient fungicide spray deposition on target surfaces. This study describes a novel spray deposition assessment protocol and determines deposition benchmarks indicative of the biological effectiveness for better interpretation of spray deposition results.
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