Citrus plants (Revised)

General Information and Agronomic practices

Introduction

Citrus is a genus of flowering plants that belongs to the family Rutaceae (citrus family). The genus comprises approximately 16 species, with several hybrids and cultivars developed over time to meet varying consumer preferences. Some of the economically significant species within the genus include well-known fruits including orange (Citrus x sinensis), lemon (Citrus x limon), grapefruit (Citrus x paradisi), lime (Citrus x aurantifolia) and Mandarins (C. reticulata). 

Citrus spp. are natives of the subtropical and tropical regions of Asia and the Malay Archipelago. They have been cultivated since ancient times, and spread to other regions of the world, including the Mediterranean, South America and southern states of USA such as California and Florida, where suitable soil and climatical conditions exist. The citrus growing belt follows the equator, extending either side of it about 35 North and 350 South latitude. It embraces tropical, subtropical and the intermediate zones.

Citrus fruits are predominantly consumed as fresh fruits due to their pleasant flavor, juiciness, and high vitamin C content. They are widely used in culinary preparations, such as salads, juices, desserts, and beverages. Citrus fruits have a reputation for their medicinal properties, primarily attributed to their vitamin C content and antioxidant properties. They are believed to boost the immune system and promote overall well-being. Citrus fruits and their peels are used in traditional medicine for various purposes, such as treating colds, indigestion, and skin conditions. 
Apart from their culinary and medicinal applications, citrus fruits find use in various industries. The essential oils extracted from citrus peels are valuable in the perfume, cosmetics, and flavoring industries. Additionally, some species of citrus trees are cultivated for ornamental purposes in gardens and landscapes. Among the common species, oranges (Citrus sinensis) are particularly noteworthy for their high nutritional value. They are an excellent source of vitamin C, providing more than the recommended daily intake in just one fruit. Oranges also contain dietary fiber, vitamin A, potassium, and various antioxidants, making them a wholesome and nutritious addition to one's diet.
The citrus industry is a substantial contributor to the global agricultural economy. Various processed products like orange juice, lemonade, and grapefruit extracts are widely available in the market. The essential oils extracted from citrus peels are used in cosmetics, aromatherapy, and food flavorings. Key producers in the citrus market include countries like Brazil, the United States, China, and Spain, which export significant quantities of citrus fruits and products to meet global demand 
(Orwa C, et al., 2009, Tran G., 2016, plantvillage (n.d)).

Species account

Species and common names
i. Founder species
1.    Citrus reticulata - Mandarin, Mandarin orange (English); Chenza (Swahili)

The mandarin orange also mandarin or mandarine, (Citrus reticulata), is a small tree originally from southern Asia and the Philippines. It is one of the original citrus species that through breeding and natural hybridization have given rise to the many commercial varieties we see. With the citron and pomelo, it is the ancestor of the most commercially important hybrids (such as sweet and sour oranges, grapefruit, and many lemons and limes). Tangerines are hybrids of mandarins mainly of mandarin with pomelo and usually have traits of mandarin but less pronounced. 
C. reticulata is a low woody shrub, evergreen tree that typically grows to a height of 3 to 8 m. Fruits are small, oblate, (flat top and bottom and wide in the middle), typically bright orange when ripe with a thin, easily peelable skin and distinctive sections, giving it the name "reticulata," which means "net-like." Flesh is easy to split into segments. In tangerines the fruits tend to be more spherical.
Mandarin and related tangerine hybrids are grown in tropical and subtropical areas. They however do better in colder climate. 
Many cultivated varieties of mandarins are seedless or have few seeds, making them more enjoyable to eat without the inconvenience of spitting out seeds. 
(Thulaja, N. R, 2005; Bekele-Tesemma, A. et al., 1993; Orwa C, et al., 2009, PFAF Plant Database. (n.d.), plantvillage (n.d)).

Pixie mandarin (Pixie orange).
Pixie is a mandarin variety propagated mainly through grafting. The trees can grow to 4 or 5 meters. Fruit: small to medium-small, usually globose to slightly oblate, and sometimes has a neck. The rind is yellow-orange, medium-thin, and not as easy to peel as tangerine. The flesh is often seedless or with one seed, orange colored, and juicy.
Pixie is the result of an open pollination of two mandarin varieties- King and Dancy (named Kincy) that took place in 1927 at the University of California Citrus Research Center, Riverside and eventually released in 1965. Pixies are a recent introduction into Kenyan farms and markets. They are generally sweeter than oranges, juicier and with more superior flavor. Pixie orange farming in Kenya is mainly concentrated in Makueni and Kitui Counties. The demand is growing within the country and currently supplies cannot meet the growing demand and hence they are more expensive than oranges.

For further reading see:
•    https://citrusvariety.ucr.edu/crc3568#:~:text=Parentage%2Forigins,and%20eventually%20released%20in%201965.
•    https://aggie-hort.tamu.edu/citrus/mandarins.html
2.    Citrus maxima - Pomelo 

The pomelo, Citrus maxima, is the largest citrus fruit, and the principal ancestor of the grapefruit. It is considered one of the three original species, with mandarin and citron, of the genus Citrus. It is therefore a natural, non-hybrid, citrus fruit, native to Southeast Asia. The pomelo is a small to medium sized tree to 10 meters or more. Leaves are large with winged petioles. The flowers white, cream to yellow.
The fruit is large, to 25 cm in diameter, and may weigh up to 2 kg. It has a thicker rind than a grapefruit. The flesh tastes like mild grapefruit, with a little of its common bitterness. The fruit generally contains a few, relatively large seeds, but some varieties have numerous seeds.

3.    Citrus medica L. - Citron 

The citron (Citrus medica) is a small evergreen, rather bushy spiny tree which has been cultivated since ancient times in India and much of South Asia. Together with pomelo and mandarin, citron is one of the primary species (parents) of the commercial Citrus fruits. From these, other citrus hybrids have developed either through natural or artificial hybridization. Hybrids of citrons with other citrus include lemons and many of the limes. 
Flowers: Purple to white or cream.  Fruit: Large to 15 cm long, oblong (long oval, protuberant at the tip, green on the outside when unripe to lemon yellow when ripe, fragrant. Fruit resembling the lemon but much larger with a thick tough skin, rough on the surface. Flesh is firm, pale yellow to white, rather dry, slightly sour to slightly sweet with many seeds. 

The thick peel makes up nearly three quarters of the fruit volume. It is the most useful part of the fruit in South Asia being used in traditional medicines, perfume manufacture, and religious purposes. It is made in to candies and it is also a source of a type of oil used as a flavoring in sweets and beverages. The pulp is mainly used as a source of other products.

Cultivated a lot in South Asia, West Indies, South and Central America and the Mediterranean region. In Africa, citron is more common in West Africa but also found in much of tropical Africa.
Source: Various. See also: http://birds.songs.free.fr/papedas.html

ii. Hybrids
4.    Citrus × aurantium Sweet Orange Group (Synonyms: Citrus sinensis, Citrus × aurantium var. sinensis). 
Common names: Orange, Sweet orange, Navel Orange, Valencia Orange (English); Chungwa (Swahili); Oranger doux (French)

Sweet orange - Citrus x sinensis is believed to have originated in Southeast Asia, specifically in the region encompassing northeastern India, Myanmar, and southwestern China. However, it is now cultivated in various parts of the world with suitable climates for citrus growth.
Orange trees are evergreen and reach heights of 6 to 15 m and can live for over a century. Most plantations have an economic lifespan of around 30 years. Leaves: glossy, dark green leaves, elliptical or oval in shape, alternately arranged on the branches. The leaves have narrowly winged petioles, a feature that distinguishes it from bitter orange, which has broadly winged petioles Flowers: white, fragrant aroma. Fruit: rather variable in color and shape, with a thick, orange-colored rind (peel) that encloses the juicy segments within. The pulp is typically divided into easily separable segments, and the fruit contains several seeds.
Orange is a widely cultivated fruit with delicious and refreshing qualities. It is consumed fresh, processed into various products, and used in salads, desserts, and beverages. Sweet orange juice is a popular and nutritious global drink. The peels are used for zest or essential oil extraction in perfume, flavoring, and cosmetic industries (Orwa C, et al., 2009, Bekele-Tesemma, A. et al., 1993, plantvillage (n.d)). 

Washington navel oranges are native to Brazil where a single orange was discovered growing as a mutation or bud-sport in 1820. Washington navel orange trees have a round, somewhat drooping canopy. The flowers lack viable pollen so the Washington navel orange will not pollinate other citrus trees. Because of the lack of functional pollen and viable ovules, the Washington navel orange produces seedless fruits. These large round fruits have a slightly pebbled orange rind that is easily peeled, and the navel, really a small secondary fruit, sometimes protrudes from the apex of the fruit.

For further reading see: https://citrusvariety.ucr.edu/crc1241A#:~:text=Parentage%2Forigins,tree%20in%20the%20early%201800s.

5.    Citrus × aurantium Grapefruit Group (Synonyms: Citrus × aurantium var. paradisi, Citrus paradisi) 
Common names: Grapefruit (English); Balungi (Swahili).

Citrus x paradisi (Citrus × aurantium Grapefruit Group) commonly known as Grapefruit is believed to be an interspecific hybrid of two citrus species: sweet orange (Citrus sinensis) and pomelo (Citrus maxima). It was first discovered in the 18th century on the Caribbean island of Barbados (West Indies). Grapefruit is now grown in various regions with tropics and the warmer subtropics. 
Grapefruit trees are medium-sized evergreen trees that can grow to a height of 5 to 6 m. Leaves: glossy and dark green. Flowers: are white and pleasantly fragrant. Fruit: is typically round or slightly oblate, and the peel color ranges from pale yellow to pink or red, depending on the variety.
Grapefruit is commonly consumed fresh, and its juicy, tangy, and slightly bitter flavor makes it a popular breakfast fruit. It is also used in salads, juices, smoothies, and cocktails. Grapefruit comes in different varieties, including white, pink, and red (also known as Ruby Red). The flesh color can vary depending on the variety, with the red varieties being sweeter and more colorful.
Grapefruit is a good source of vitamins and minerals, particularly vitamin C, potassium, and dietary fiber. Grapefruit is known for its potential health benefits, including aiding digestion, supporting the immune system, and promoting heart health. Seed extract, derived from the seeds and pulp of the fruit, is sometimes used as a natural antimicrobial agent in alternative medicine. Unlike some other citrus species, grapefruit is less commonly used for producing essential oils or as a rootstock for grafting other citrus varieties because yields on this stock are low.
(PROSEA, 2016, Orwa C, et al., 2009, plantvillage (n.d)

6.    Citrus x aurantifolia
Common names: Lime, Key lime, Acid lime (English); Ndimu (Swahili)

Citrus x aurantifolia is a small, evergreen tree that typically grows to a height of 3 to 4.5 m with thorny branches and glossy. Leaves; Oval, rather small, shiny green 4–8 cm, the leaf stalk with a narrow “wing”, an extra leafy growth and a “joint” with the leaf blade, edge smooth or round-toothed. Flowers; Both buds and flowers white. Fruits: oval, a thin, smooth, yellow-green rind that turns yellow when fully ripe. The flesh is juicy, acidic, and highly aromatic, filled with small seeds. Lime is widely used in cooking and medicine due to its highly acidic juice. It is a popular ingredient in cuisines worldwide, especially in desserts like Key lime pie, sauces, marinades, and beverages. The fruit's rind contains aromatic oils used in perfumes, cosmetics, and cleaning products. Lime trees are also grown for their attractive foliage and fragrant flowers, serving as ornamental plants.
(Bekele-Tesemma, A. et al., 1993, Orwa C, et al., 2009, plantvillage (n.d).

7.    Citrus × limon (Syn: Citrus limon)- 
Common names: Lemon (English); Limau (Swahili)

Lemon - Citrus x limon is thought to be a hybrid between the citron (Citrus medica) and the sour orange (Citrus × aurantium). Presumably native to southern Asia, now widely cultivated in all subtropics and occasionally in the tropics. Its adaptability to diverse environments has contributed to its widespread presence in tropical, subtropical, and some temperate regions.
Lemon trees are small to medium-sized evergreen trees, typically reaching a height of 3 to 6 m with stout stiff spines. Leaves: are glossy green. Flowers: fragrant, white with a hint of purple. Fruits: generally, round or oval, with a bright yellow rind that contains essential oils giving them their distinct aroma. Lemons are a fundamental ingredient in various cuisines and culinary applications. Their tangy and refreshing flavor enhances dishes, desserts, and beverages. Lemon juice is a popular natural acidifier, preservative, and flavor enhancer used in cooking, baking, and making refreshing lemonades.
Lemons also have numerous non-culinary uses. They are a rich source of vitamin C, known for its immune-boosting properties. Lemon essential oil, extracted from the peel, is used in aromatherapy for its invigorating scent. The citric acid found in lemons makes them a natural cleaning agent, effectively removing stains and odors.
Lemons are valued for their versatility, tangy taste, and high citric acid content. They stand out for their widespread use in both culinary and non-culinary applications, making them a staple in households, restaurants, and industries alike 
(PROSEA, 2016, Orwa C, et al., 2009, plantvillage (n.d)).

8. Rough lemon (Citrus x jambhiri Lush.) also Rough skin lemon is one of the most vigorous rootstocks used with citrus, under favorable conditions producing a very large tree, and has seen widespread use around the world. It reproduces true from seeds. Rough lemon is believed to have originated in northern India where it grows wild. It is naturalized in the West Indies and Florida. Rough lemon is believed to be a cross between a mandarin and a citron. The fruit can be used at any stage of ripeness and is often made into juices.
It is a tree of medium size and thorny; Fruit oblate, rounded or oval; base flat to distinctly necked; apex rounded with a more or less sunken nipple of medium size; peel lemon-yellow to orange-yellow, rough and irregular, with large oil glands. 

Source: Various. See: http://citruspages.free.fr/lemons.php

9.    Citrus × aurantium var. clementine
Common name: Clementine

Citrus varieties of commercial importance include the following:

• Oranges: 'Washington Navel' (alt: 1000-1800 m above sea level), 'Valencia Late', 'Hamlin' and 'Pineapple' (all alt from 0 - 1500 m above sea level)
• Mandarins: 'Kara', 'Satsuma' (0-1500 m above sea level), 'Clementine', 'Dancy' (0-1800 m above sea level), 'Pixie', 'Encore' and 'Kinnow'
• Tango/ Tangelo (hybrids of mandarins): 'Temple' a Tango (mandarin x orange) and 'Minneola' a Tangelo (mandarin x grapefruit)
• Grapefruit: 'Marsh Seedless', 'Duncan' and 'Ruby Red', 'Red Blush' (0-1500 m above sea level) and 'Thomson' (1000-1500 m above sea level)
• Lemons: 'Meyer', 'Eureka', 'Lisbon' and 'Villa Franca' (1000-1500 m above sea level), Rough lemon (0-1500 m)
• Limes: 'Mexican', 'Tahiti' and 'Bears' (0-1500 m)

Note: All varieties mentioned are available in Kenya, particularly in Kenya prison farms, albeit their commercial availability is a problem due to citrus greening disease, which is prevalent in Kenya in all areas above 900 m altitude. Since there is no citrus certification scheme in Kenya, there is no assurance that planting material derived from any Kenyan nursery is greening disease-free.

Ecological information

Citrus species can thrive in a wide range of soil and climatic conditions. Citrus is grown from sea level up to an altitude of 2100 m but for optimal growth a temperature ranges from 2deg to 30deg C is ideal. Long periods below 0deg C are injurious to the trees and at 13deg C growth diminishes. However, individual species and varieties decrease in susceptibility to low temperatures in the following sequence: grapefruit, sweet orange, mandarin, lemon/lime and trifoliate orange as most hardy. Temperature plays an important role in the production of high quality fruit. Typical coloring of fruit takes place if night temperatures are about 14deg C coupled with low humidity during ripening time. Exposure to strong winds and temperatures above 38deg C may cause fruit drop, scarring and scorching of fruits. In the tropics the high lands provide the best night weather for orange color and flavor.
Depending on the scion/ rootstock combination, citrus trees grow on a wide range of soils varying from sandy soils to those high in clay. Soils that are good for growing are well-drained, medium-textured, deep and fertile. Waterlogged or saline soils are not suitable and a pH range of 5.5 to 6.0 is ideal. In acidic soil, citrus roots do not grow well, and may lead to copper toxicity. On the other hand at pH above 6, fixation of trace elements take place (especially zinc and iron) and trees develop deficiency symptoms. A low pH may be corrected by adding dolomitic lime (containing both calcium and magnesium)
 
 A citrus orchard needs continuous soil moisture to develop and produce, and water requirement reaches a peak between flowering and ripening. However, many factors such as temperature, soil type, location, plant density and crop age influence the quantity of water required. Well-distributed annual rainfall of not less than 1000 mm is needed for fair crop. In most cases, due to dry spells, irrigation is necessary. Under rain-fed conditions, flowering is seasonal.
There is a positive correlation between the onset of a rainy season and flower break. With irrigation flowering and picking season could be controlled by water application during dry seasons. Irrigation systems involving mini sprinklers irrigating only soil next to citrus trees have been developed as an efficient and water conserving irrigation method. 

Agronomic aspects

Propagation
The most common method of citrus propagation is by budding. When old trees are top-worked, bark grafting is used. Citrus varieties grown from seed have numerous problems like late bearing, uneven performance due to their genetic variability and susceptibility to drought, root invading fungi, nematodes and salinity. Rootstocks are therefore used to meet all citrus requirements (tolerance / resistance to pests and diseases, suitability to soil and water conditions, as well as compatibility with scion variety selected). Rootstocks also improve the vigour and fruiting ability of the tree, as well as the quality, size, colour, flavour and rind-thickness of the fruit.

Citrus rootstocks have the following characteristics: 
 
•    Rough lemon (C. jambhiri). Seedlings produce a uniform and fast growing rootstock, which is easy to handle in the nursery. The plant develops a shallow but wide root system with a vigorous taproot. Trees budded on rough lemon produce an early, good yield but the fruit quality especially during the first years is not satisfactory. Trees are comparatively short-lived. Rough lemon prefers deep, light soil and do not tolerate poor drainage or waterlogging. It is tolerant to citrus tristeza virus but susceptible to Phytophthora spp., citrus nematodes and soil salinity. It is drought tolerant. Rough lemon can be budded with oranges, mandarins, lemons, limes and grapefruits. It is the most commonly used rootstock in East Africa.
•    Cleopatra mandarin (Citrus reshni). It is suited to soils of heavier texture. On this rootstock, trees are slow growing with low yields in early years. Trees are long-lived. Its influence on fruit quality is good. It is tolerant to soil salinity. It is susceptible to poor drainage, Phytophthora spp. and citrus nematodes. It can be budded with oranges, mandarins and grapefruits.
•    Trifoliate orange, Citrus trifoliata (syn. Poncirus trifoliata), It is a dwarfing stock and is most suitable for heavy and less well-drained soils. Rootstock propagation is slow, but budded trees yield heavily and produce high quality fruits. The plants develop abundant roots and often several taproots, which penetrate the soil deeply. It should not be used in calcareous soils. It is tolerant to Phytophthora spp. and citrus nematodes. It can be budded with oranges, mandarins and grapefruits.
•    Carrizo / Troyer citrange (Citrus trifoliata x C. sinensis). Rootstocks are somehow difficult to establish. In order to promote fibre roots, young plants should be undercut as long as they are in the seedbed. Citranges are not suitable for very light and strongly alkaline soils. They are sensitive to overwatering but once established produce high quality fruits. They are somehow tolerant to Phytophthora spp. and citrus tristeza virus but susceptible to Exocortis viroid and citrus nematodes. They can be budded with oranges, mandarins and grapefruits.
•    Citrumelo (Citrus trifoliata x C. paradisi). Plants produce an expansive root system and therefore have good drought tolerance. They can be used on a wide range of soils and produce an outstanding quality of fruit. They are tolerant to Phytophthora spp. but susceptible to citrus nematodes. They can be budded with oranges, tangerines and grapefruit.
•    Rangpur lime (C. aurantifolia). This stock is suitable for various soil types, including deep sand. It prefers warm locations. It produces vigorous, well-bearing trees with a high degree of drought resistance. It is susceptible to Phytophthora spp. and citrus nematodes. It can be budded with oranges and grapefruits.
•    Sweet orange (C. sinensis). This rootstock produces large and vigorous trees and is suitable for light to medium soils, which are well drained. It produces good quality fruits and the trees are long-lived. It has low drought tolerance and is very susceptible to Phytophthora spp. and citrus nematodes. It can be budded with oranges, mandarins and grapefruits.
•    Sour orange (C. aurantium). An excellent rootstock in locations where citrus tristeza virus is not a problem since it is very susceptible to the disease. It is tolerant to poor drainage. It has low tolerance to drought. It produces very good quality fruits. It is tolerant to Phytophthora spp. but susceptible to citrus nematodes. It can be budded with oranges and grapefruits.
 
Planting
•    Select seeds from healthy mother trees for rootstocks
•    Hot water treat seeds at 50deg C for 10 minutes
•    Seeds perform better when planted soon after they are extracted
•    Sow seeds in seedbeds or polybags (18 x 23 cm). Seeds germinate in 2 to 3 weeks
•    Water the seeds regularly, preferably twice a day until they germinate
•    Seedlings are normally ready for budding when reaching pencil thickness or 6 to 8 months after germination.
•    T-budding is the most common method.
•    Do budding during warm months. Avoid budding during cold periods and during dry conditions
•    Budded plants are ready for transplanting 4 to 6 months after budding
Alternatively, obtain budded plants from a registered fruit nursery. These budded plants should be ready for transplanting in the field.

Transplanting in the field
•    Transplant in the field at onset of rains.
•    Clear the field and dig planting holes 60 x 60 x 60 cm well before the onset of rains.
•    At transplanting use well-rotted manure with topsoil.
•  Spacing varies widely, depending on elevation, rootstock and variety. Generally, trees need a wider spacing at sea level than those transplanted at higher altitudes. Usually the plant density varies from 150 to 500 trees per ha, which means distances of 4 x 5 m (limes and lemons), 5 x 6 m (oranges, grapefruits and mandarins) or 7 x 8 m (oranges, grapefruits and mandarins). In some countries citrus is planted in hedge rows.
•    It is very important to ensure that seedlings are not transplanted too deep.
•  After transplanting, the seedlings ought to be at the same height or preferably, somewhat higher than in the nursery.
•    Under no circumstances must the graft union ever be in contact with the soil or with mulching material if used.
 
Tree management / maintenance
•    Keep the trees free of weeds.
•    Maintain a single stem up to a height of 80-100 cm.
•    Remove all side branches / rootstock suckers.
•    Pinch or break the top branch at a height of 100 cm to encourage side branching.
•    Allow 3-4 scaffold branches to form the framework of the tree.
•    Remove side branches including those growing inwards.
•    Ensure all diseased and dead branches are removed regularly.
•    Careful use of hand tools is necessary in order to avoid injuring tree trunks and roots. Such injuries may become entry points for diseases.
•    As a general rule, if dry spells last longer than 3 months, irrigation is necessary to maintain high yields and fruit quality. Irrigation could be done with buckets or a hose pipe but installation of some kind of irrigation system would be ideal.
•    Citrus is under irrigation in the major citrus world producing countries.
 
Manure and fertilizer
For normal growth development (high yield and quality fruits), citrus trees require a sufficient supply of fertiliser and manuring. No general recommendation regarding the amounts of nutrients can be given because this depends on the fertility of the specific soil. Professional, combined soil and leaf analyses would provide right information on nutrient requirements. In most cases tropical soils are low in organic matter.
To improve them at least 20 kg (1 bucket) of well-rotted cattle manure or compost should be applied per tree per year as well as a handful of rock phosphate. On acid soils 1-2 kg of agricultural lime can be applied per tree spread evenly over the soil covering the root system. Application of manure or compost makes (especially grape-) fruits sweeter (farmer experience).
Nitrogen can be supplied by intercropping citrus trees with legume crops such as mucuna, cowpeas, clover or dolichos beans, and incorporating the plant material into the soil once a year. Mature trees need much more compost/well-rotted manure than young trees to cater for more production of fruit. Conventional fertilization depend on soil types, so it is recommended to consult the local agricultural office.
 
Husbandry
In windy areas, a windbreak should be provided as citrus is sensitive to strong winds. A windbreak provides protection at orchard tree level for about 4-6 times its height.
•    Plant the windbreak as close as possible and at right angles to prevailing winds.
Symptoms of mineral deficiency

Intercropping
Intercropping with shallow rooted crops such as vegetables, herbs, green manure legumes sweet potatoes etc, is recommended in order to keep the soil cultivated around citrus trees.

Harvest, post-harvest practices and markets 

Harvest
Citrus fruits are best harvested when they are mature, as this ensures they have developed their full flavor and nutritional content. The maturity of citrus fruits can be identified by changes in their color, especially in regions where the night temperatures are around 14°C and there is low humidity. As the fruits ripen, their color transforms from green to vibrant shades of orange, yellow, or pink, depending on the variety.
In low-altitude areas citrus fruits may not change color, it becomes necessary to conduct maturity tests. A sample of fruits can be randomly selected and examined for signs of maturity, such as firmness, size, and internal juice content. This practice ensures that fruits are harvested at the optimal time for maximum quality.
During harvesting, it is essential to handle the fruits with care to maintain their good condition. Use of a sharp knife is recommended to cut the fruits from the tree carefully. By employing this method, growers can avoid damaging the fruits and ensure a clean cut, reducing the risk of bruising and post-harvest injuries.
Alternatively, some farmers may opt to pluck the fruits directly from the tree by hand. This technique has its drawbacks as it often leads to the stem breaking too close to the fruit. When the stem is broken in such a way, it creates an entry point for potential infections, pests, or diseases that could affect the fruit's quality during storage and transportation.

Post-harvest practices
After harvesting, the fruits are thoroughly cleaned to remove any dirt or residues. Grading involves sorting the fruits based on their size, color, and overall quality. This ensures that consumers receive uniform and visually appealing fruits. Deformed and infected fruits are discarded. Finally, the citrus fruits are carefully packed in aerated containers, such as boxes or crates, to protect them during transportation.
To extend the shelf life of citrus fruits, post-harvest treatments like waxing and cold storage are commonly used. Applying a thin layer of wax to the fruit's surface helps reduce moisture loss and preserves freshness. Cold storage, at controlled temperatures, slows down the ripening process and minimizes spoilage.
(Strano, M.  et al.,2022.

Value addition and markets 

The citrus fruit market is vast and diverse, with both local and global demand. Locally, citrus fruits are sold in grocery stores, supermarkets, and farmer's markets. They are also used in various food and beverage industries to make juices, jams, and flavorings.
Export plays a significant role in the citrus fruit market. Many citrus-producing countries export their surplus to international markets. The major export destinations include North America, Europe, and Asia. Factors like taste, freshness, and price influence the competitiveness of citrus fruits in these markets.
Pixie oranges are gaining importance in the Kenyan market. They are mainly produced in Makueni and Kitui counties. The recommended spacing is about 3-4 within rows and about 5m between the rows. A hectare can fit about 900 trees giving about USD 20,000 per year. A grafted tree can give 60 kg per year and will start bearing fruit after 2-3 years. High yields are attained at about the 5th year, by when a tree may have 300 or more fruits.
 

Nutritional value and recipes

Nutritive value per 100 g of edible portion

Source (Nutrient data): FAO/Government of Kenya. 2018. Kenya Food Composition Tables. Nairobi, 254 pp. http://www.fao.org/3/I9120EN/i9120en.pdf

^a Lewis, J. 2019. Codex nutrient reference values. Rome. FAO and WHO

^b NHS (refers to saturated fat)

^c https://www.hsph.harvard.edu/nutritionsource/water/

^d British Heart Foundation

^e FDA

^f NIH

^g Mayo Clinic

Recipes
1. Kenyan Kachumbari (Salad)

Ingredients
3 medium sized onions
4 medium sized tomatoes
Salt to taste
3 tbsp lemon juice 
2 tbsp chopped dhania
1 green chili
Preparation
•    Peel and slice onions very thinly
•    Sprinkle them with salt and keep aside for sometime 
•    Gently squeeze the onions until soft. This helps in removing the bitterness from them
•    Rinse with clean water
•    Squeeze out excess liquid 
•    Slice tomatoes very thinly and mix with dhania, lemon, salt and green chili
•    Add in the onions and mix
•    Serve
Source: Adeka et al., 2005

2. Endimawu (Enimu) (Lemon water)
Source: Banyoro of Hoima, Uganda (Maundu et al. 2005)
Ingredients: Lime or lemon, water, sugar – optional

Procedure:
Cut limes into two halves
Prepare black tea in the normal way
Squeeze each half at a time to release its juice. You can squeeze directly into clean water or black tea
Mix by stirring. 
Add a little sugar to taste (optional)

Served with: 
Snacks e.g. bread, biscuits or other foods

Comments:
Lemon water is taken for cough, weight loss, diabetes or high blood pressure. Others used for making such flavoured drinks include lemon grass in its dried or fresh form. It is said to be good for constipation.

3. Mlenda with lemon 
Ingredients
500 g bunches of mlenda (Jute, Corchorus olitorius)
2 medium sized tomatoes (diced)
1medium sized onion (diced)
¼ cup lemon (juice)
4tbsp peanut butter
3 tbsp ghee
1 cup coconut milk
Salt to taste
Preparation
•    Pluck the leaves from the stalks
•    Wash thoroughly and cut the leaves into small pieces
•    Sprinkle the leaves with lemon juice and mix well
•    Heat the ghee, fry onion lightly, add tomato and season to taste, stir
•    Add the leaves, stir and cook for 10 minutes 
•    Mix groundnut powder with coconut milk, add in the cooking vegetable and stir
•    Simmer for 5 minutes 
•    Serve with rice
Lemon juice removes the slimy consistency from the vegetable. The vegetable has a slight lemon taste
Source: Adeka et al., 2005

Fresh Quality Specifications for the Market in Kenya

The following specifications constitute raw material purchasing requirements.

© S. Kahumbu, Kenya