2 - University of Limpopo

UNIVERSITY OF LIMPOPO 

TURFLOOP CAMPUS 

FACULTY OF SCIENCE AND AGRICULTURE 

SCHOOL OF AGRICULTURAL AND ENVIRONMENTAL SCIENCES 

DEGREE AND DIPLOMA EXAMINATIONS 

MODULE : PLNP451 MAY/JUNE : 2012 

(CITRUS PRODUCTION) 

TIME : 3 HOURS PAPER : P1 

INTERNAL EXAMINER : Mr. T.P. MAFEO (UL) 

EXTERNAL EXAMINER : 

MARKS : 100 

THIS PAPER CONSISTS OF …6…PAGES INCLUDING COVER PAGE 

INSTRUCTIONS: 

1. Answer all questions 

2. Write neatly and legibly 

3. Answer all questions in order of appearance

2 

PLNP451 MAY/JUNE EXAMINATION 2012 

QUESTION 1 [26] 

Discuss with the help of Figure 1 the physiological relationship between leafy 

versus leafless inflorences to citrus fruit bearing probabilities. 


Briefly, outline the metabolic changes associated with growth and development 

of citrus fruit as shown on Figure 2. 


Use the information supplied in a fertilization program for Midknight 

Valencia Sweet Oranges at Mahela Citrus Boerdery (Table 1) to calculate 

total amount of KCℓ required for September application. In your calculation, 

please ensure that all the steps are shown and convert the required amount 

into equivalent of 50 kg bags. Given that the orchard has 416 Midknight 

Valencia Sweet Oranges trees per ha and the specific orchard is 4 ha in 

size. 


Briefly, elucidate how the different maturity parameters for citrus fruit are 

measured to ensure that export fruits meets minimum set maturity standards. 


5.1. a) List the four South African citrus sectors. (2) 

b) State how much in total is each earning annual in foreign (5) 

excahnge? 

5.2 Which climatic conditions allow the production of wide range of citrus (4) 

types/sectors throughout South Africa? 

5.3 Name the different stakeholders and their responsibilities in South (13) 

Africa citrus industry that came as the results of deregulation of this

3 

industry in1997. 


5.4 Describe the three zones in which greening disease (3) 

(Huanglongbing) occur based on the severity of the disaese.

4 


Appendices 

Leafless flower shoot 

Leafless flower shoots 

Figure 1: Relationship between leafy versus leafless inflorences to citrus fruit 

bearing probabilities. 

Citrus flowering Shoots

5 


Figure 2: Metabolic changes associated with the growth and development citrus 

fruit. (B) Citrus fruit growth phases, (C) Chlorophyll degradation and carotenoid 

biosynthesis, (D) Soluble carbohydrates translocation and (E) Acid accumulation 

in fruit pulp.

6 


Table 1: A typical citrus fertilization program at Mahela Boerdery Letsitele on 

2012 production season, Tzaneen. 

Orchard: Orchard 20 Size: 4.0ha 

Cultivar/Variety: Midknight Valencias 

Oranges 

Trees per ha: 416 

Fertiliser Quantity Time of Application 

Soil Applications g per tree 

Limestone Ammonium Nitrate (LAN) 550 July 

LAN 250 August 

LAN 250 September 

Potassium Chloride (KCL) 550 September 

Dolomitic Lime 4000 October 

Foliar Sprays g/ 100ℓ water 

Low Biuret Urea 1000 July 

Manganese Sulphate 200 October 

Solubor® 150 October

7 


MEMO 


Citrus fruit set is highly dependent upon the type of inflorescence (2). In general, 

leafless inflorescences emerge first (2) and contain a bouquet of flowers with low 

probability to set fruit (1). On the other hand, flowers in leafy inflorescences that 

can be terminal (2) or distributed among leaves along the shoot (2) are 

commonly associated with higher fruit set (2). 

Usually, late-opening flowers remain attached to the tree longer than earlyopening 

flowers (2) and flowering shoots with a high leaf-to-flower ratio have the 

highest fruit set (2). The positive influence of leaves on fruit set appears to be 

associated with increased net CO2 assimilation (2) and supply of 

photoassimilates from developing leaves (2). These might also influence ovary 

growth (2) and fruit set (2) through the provision of gibberellins since leafy 

inflorescences contain higher hormonal levels than leafless ones (2). 


The sub-figure B shows the three phases of citrus growth and development (1). 

Fruit growth is mostly due to cell divisions during phase I (1) and to water 

accumulation (1), and therefore cell enlargement, during phase II (1). At the 

beginning of phase III, growth is arrested (1) and fruit starts a non-climacteric 

ripening process (1). The sub-figure C shows decline in rind chlorophyll and the 

onset of carotenoid accumulation almost coincides with the disappearance of 

chlorophyll (1). In contrast with peel flavedo, chlorophyll degradation and 

carotenoid biosynthesis in pulp proceed along phase II and therefore colour 

break is reached earlier (1). This results in a progressive change in pulp colour 

that contrasts with the rapid colour break occurring in flavedo (1). The sub-figure 

D shows the carbohydrates metabolical changes in the ripening citrus fruit (1). 

Paralleling fruit growth, high amounts of soluble carbohydrates are translocated 

to the developing fruit (1). Thus, mature citrus fruit pulp accumulates high

8 


amounts of sucrose, glucose and fructose (1) in a 2:1:1 ratio (1). The sub-figure 

E shows acid metabolic changes in ripening citrus fruit. (1). Acid accumulation in 

fruit pulp takes place during phase I and the beginning of phase II, reaching a 

maximum around mid-phase II (1). Organic acids are catabolized through the 

end of phase II (1) to attain during phase III the characteristic low acidity of ripe 

fruits (1). 

KCℓ Application in September 


1. Number of trees in orchard = Orchard in size (ha) x Number of trees/ha 

= 4,0 ha x 46 

= 1164 trees in the orchad 

2. Total number of KCℓ required = KCℓ required/tree (grams) x Number of trees 

3. Conversion to kilogram (Kg) 

4. Conversion to 50kg bags 

in orchard 

= 550g x 1664 trees 

= 915 200g 

= 915 200g/1 000 

= 915,2kg 

= 915,2kg/50kg 

= 18 bags of 50kg of KCℓ 


a) Fruit Colour (1) 

It is measured against a colour chart (1). In citrus industry, peel colour is not a 

reliable indicator of maturity (1). They are different charts used for the various 

types of citrus (1).

) Juice percentage (1) 

9 


It is determined by weighing a sample of twelve selected harvested fruit (1). The 

juice from these fruit is then extracted, filtered and weighed (1). Then, the juice 

percentage is determine by dividing juice weight with total weight of 12 sampled 

fruit (1). 

c). Total Soluble Solids (TSS)/Brix (Sugar content) (1) 

In citrus industry sugar content is known as °Brix (1), which is a measure of TSS 

in juice or concentrate (1). Brix is usually reported as “degrees brix” and is 

equivalent to percentage (e.g. citrus juice with 12 °Brix has 12 % TSS) (1). It is 

measured using refractometers (1), which are avalable in both hand-held and 

digital forms (1). 

d) Acid Content/ Titratable Acid (TA) (1) 

Citrus juice sourness is measured by volumetric titration with standardized 

sodium hydroxide, using phenolphthalein as internal indicator (1). This method 

measures mainly the citric acid, which is 70 to 90% of acid in the sample (1). 

e) Brix/Acid ratio (1) 

It is relative sweetness or sourness of citrus fruit (1), which is determined by ratio 

of sugars to acid (1). It is simple a quotient of °Brix divided by percentage TA (1). 

1.1. a. Sweet orange - 3 billion rand 

b. Soft citrus - 500 million rand 

c. Grapefruit - 600 million rand 

d. Lemon & limes - 400 million rand (6) 


1.2. The climatic conditions that allow production of wide range of citrus 

types/sectors in SA are mild and almost frost-free winters, which range from

10 


latitudes 17°S to 34°S where temperature is seldom drops below - 20C and 

almost never - 30C. (4) 

1.3. a. Citrus Growers Association – it is responsible for research, playing a role 

in transformation, information and market access. 

b. Citrus Exporters Forum – it is established to look at the export side and what 

is going on market. 

c. Citrus Academy – it is responsible for training and skills development in the 

citrus sector. 

d. Citrus Research International – it does research work and looks at the 

technical side of market access. (13) 

1.4 a) Zone A, which is regarded as where highest incidence of the diseases 

occurs 

b) Zone B, where the incidence of greening is moderate 

c) Zone C, where the incidence of grening disease is low (3)

UNIVERSITY OF LIMPOPO 

TURFLOOP CAMPUS 

FACULTY OF SCIENCE AND AGRICULTURE 

SCHOOL OF AGRICULTURAL AND ENVIRONMENTAL SCIENCES 

DEGREE AND DIPLOMA (SUPPLEMENTARY/AEGROTAT) EXAMINATIONS 

MODULE : PLNP451 MAY/JUNE : 2012 

(CITRUS PRODUCTION) 

TIME : 3 HOURS PAPER : P1 

INTERNAL EXAMINER : Mr. T.P. MAFEO (UL) 

EXTERNAL EXAMINER : 

MARKS : 100 

THIS PAPER CONSISTS OF …3…PAGES INCLUDING COVER PAGE 

INSTRUCTIONS: 

1. Answer all questions 

2. Write neatly and legibly 

3. Answer all questions in order of appearance

2 

PLNP451 MAY/JUNE (SUPPLEMENTARY/AEGROTAT) 

EXAMINATION 


2012 

1.1. a) On which factors are packhouse designs based? (5) 

b) Name three major citrus fruit market segments. (6) 

c) Enlist five major fundamental operations that need to be perform 

in citrus fruit packhouse. (10) 

d) On which stages/steps of citrus fruit packhouse is fungicide 

applied? (4) 

1.2. a) What is de-greening process? (2) 

b) Enlist five factors that contribute to de-greening atmosphere in the 

de-greening room. (5) 


2.1. Explain in your own words what you understand by maximum 

residue levels. (5) 

2.2. Where can citrus growers and packhouses find more information 

about MRLs? (4) 

2.3. Where can growers and packhouses find more information 

about citrus fruit packing specifications? (2) 

2.4. Which two factors are used by the Perishable Products Export and 

Control Board (PPECB) inspectors when they come onto the farm 

into the packhouse to do inspections? (4) 


3.1. a) What is the significance of citrus rind scarring in fruit quality?, (5) 

b) Give three major causes of citrus fruit rind scarring (6) 

c) And for each provide one example as differentiated by their 

symptoms. 

(2)

3 


EXAMINATION 


4.1. What are the climatic descriptions of the following climatic zones 

suitable for citrus production in South Africa? 

2012 

a. Semi-desert regions (3) 

b. Cold production regions (3) 

c. Cool, inland production regions (2) 

d. Intermediate production regions (3) 

e. Hot production regions (4) 

4.2. Discuss pre-planting fertilisation phase as one of the three phases of 

a citrus fertilization program. (16) 

4.3. Briefly explain the main objectives of performing proper training and 

pruning as cultural practices in citrus trees. (9) 

MEMO 

QUESTION ONE [32]

4 


EXAMINATION 

1.1 a) 1. Quantity of fruits (1), 

2. Cultivar/type of citrus being packed (1), 

3. Requirements of growers, whose fruit are being packed (1), 

4. Markets that fruit will go to (1) and 

5. Available manpower (1). 

b) 1. Export market (2) 

2. Local market (2) 

3. Juice processing market (2) 

c) 1. Separating fruit – according three major market segments (2) 

2012 

2. Applying treatments and process – packhouse must design way that right 

treatment and process are applied to right fruit at right time (2) 

3. Meet market requirements – packhouse must ensure that the process and 

package right fruit as per market destined for (2) 

4. Enable tracing and tracking – packhouse process needs to ensure traceability 

of fruit throughout flow (2) 

5. Fruit quality and safety – quality and safety of fruit must always be maintained 

through the flow (2) 

d) 1. Dumping site (2) 

2. Fungicide washing bath (2) 

1.2. a) It is the process of enhancing citrus fruits colour from green to yellow, 

which is more desirable colour. 

b) Ethylene (1), temperature (1), humidity (1), air circulation (1) & ventilation and 

atmospheric composition (1) 


2.1. MRLs are defined as the maximum concentration of pesticide residue 

(expressed as milligrams of residue per kilogram of food/animal feeding stuff) 

likely to occur in or on food and feeding stuffs after the use of pesticides 

according to Good Agricultural Practice (GAP), i.e. when the pesticide has been 

applied in line with the product label recommendations and in keeping with local

5 


EXAMINATION 

2012 

environmental and other conditions). MRLs are primarily trading standards, but 

they also help ensure that residue levels do not pose unacceptable risks for 

consumers (5). 

2.2. Citrus Growers Association (2) and Citrus Research International (2) 

2.3. Department of Agriculture, Forestry and Fisheries (DAFF) (2) 

2.4. The first factor relates to general requirements, and these in fact will apply to 

all citrus fruits (2). The second factor refers to internal and external quality 

standards (2). 


3.1. a) Citrus fruit rind scarring is important in fruit quality since fruit with scarring 

symptoms are culled and downgraded during pre-sorting and packaging stages 

in the packhouse (3). Furthermore, citrus fruit with scars are susceptible to 

postharvest decaying as result of easy entry by microorganisms (2). 

b) The three major causes of citrus fruit scarring are biological (2), mechanical 

(2) and chemical damages (2) and c) their examples are biological (insects, 

mites and diseases) (1), mechanical (wind, hail and equipment) (1) and chemical 

(phytotoxic burn) (1). 


4.1. a. Semi-desert regions – these areas are characterised by extreme hot 

summers (1) and cold winters (1) with the occurrence of frost (1) 

b. Cold production regions – these are semi-coastal areas situated in southern 

latitudes (1), between 23°30’and 34°30’S (1) in Eastern, Southern and Western 

Cape (1) 

c. Cool, inland production regions – occurs on high-lying areas (1) (above 900 m 

elevation) (1) 

d. Intermediate production regions- falls between hot, low-lying areas (1) and 

cool, high-lying areas (1), i.e. between 600 and 900 m elevation (1)

6 


EXAMINATION 

2012 

e. Hot production regions- these are areas with-hot humid(1) (< 300 m elevation) 

(1) & hot dry (1) (300-600 m elevation) (1) 

4.2. Soil Preparation & Pre-Plant Fertilization 

• Before establishing citrus orchard it essential to prepare soil correctly. 

• Soil suitability & correct method soil preparation can determine by 

inspecting soil profile pit. 

Liming 

• Lime requirement determine by timeous soil analysis before soil 

preparation. 

• It depends on level soil acidity (between 6.0 & 7.2). 

• If liming recommended based soil analysis, two possible limes (dolomitic 

or calcitic) can used. 

• Depending on calcium & magnesium ratio in soil, anyone can use. 

• Lime should applied 3-6 months prior planting 

• When applying lime should broadcast and deeply ploughed-in (500- 

600mm) 

Phosphorus requirement 

• Since P immobile element needs incorporated prior planting 

• If supers used, about 1000 kg/ha should applied. 

• Methods to apply P: 

1. Strip application 

2. Ridges 

3. Planting hole 

4.3. 1. To control pests and diseases in the citrus orchard by remove diseased 

branches and encouraging air circulation. 

2. To increase the leaf the total effective leaf area and promote photosynthesis 

by exposing the leaves light and air. 

3. To keep the tree in the right size, so that the grower can easily manage his 

orchard.

7 


EXAMINATION 

2012

2 - University of Limpopo

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