Sunday, April 3, 2011

THE MANKETTE: MONGONGO NUT TREE (Schinziophyton rautanenii)

OVERALL OBJECTIVE

To review the characteristics, growth requirements, distribution and importance of mungongo tree (Schinziophyton rautanenii)

SPECIFIC OBJECTIVES
  • To establish the importance of mongongo in oil production.
  • To establish the potential of mungongo in production of other products besides oil.

INTRODUCTION
The mungongo tree (Schinziophyton rautanenii) occurs naturally in Southern Africa and is a staple food in the Kalahari among the hunter gatherers (Graz 2007).Archaeological evidence has shown that they have been consumed amongst San communities for over 7000 years and their popularity stems in part from their flavour and in part from the fact that they store well and remain edible for much of the year (Wikipedia 2009).In its core distribution areas where its abundant, nutritional value and reliability equals many cultivated staple crops. Outside its core area it is eaten but not as a staple (Agro forestry tree database 2009).The mungongo tree is most important in that the nuts have edible oil which is extracted and is locally used in food preparation and personal care products and can also be used in manufacturing industries for production of various products (Julian et al 2009).

LITERATURE REVIEW


SCIENTIFIC CLASSIFICATION

Kingdom  : Plantae
Division   :Magnoliophyta
Class        : Magnoliopsida
Order       :Malpighiales
Subfamily: Crotonoideae
Tribe       : Ricinodendreae
Genus      :Schinziophyton
Species    : Rautanenii Authority: (schinz) Radcl- sm
Synonyms: Ricinodendron rautanenii Schinz (Wikepedia 2009).


COMMON NAMES
English- mankett tree, wild akkernut, featherweight tree.
Tswana- mongongo
Bemba – mukusu (Agroforestry tree database 2009).
! Kung Bushmen - //Xa, mongongo
Lozi – mungongo
Herero – mangetti, mongongo
Kwangwali – ugongo, ngongo
Shona – mungomangoma
Afrikaans – wilde okkerneut (Natural hub 2009).
ORIGIN AND GEOGERAPHICAL DISTRIBUTION
Distribution of S.rautanenii in Africa





The tree is distributed widely throughout Southern Africa. There are several distinct belts of distribution, the largest of which stretches from northern Namibia into northern Botswana, South- western Zambia and Western Zimbabwe. Another belt is found in Eastern Malawi and another in Eastern Mozambique (Wikipedia2009). It is sometimes planted in southern DR Congo and Zambia. It has been planted on a trial basis in Israel, but productivity there seems to be very low (Graz 2007).

ECOLOGY
Schinziophyton rautanenii occurs as scattered trees or small localized stands. It grows on wooded hills, in bush veld, on sandy ridge tops, sometimes on alluvial margins of major rivers and limestone outcrops (Ronne and Joker 2006). In the area where it occurs the mean annual temperatures are about 20°C, and the maximum daily temperatures often exceed 30°C; the plant tolerates light frost, but temperatures below 7°C kill seedlings (Graz 2007).The tree is found between 5˚S and 23˚S and occurs at 200–1500 m altitude and grows well when the annual rainfall is 200–1000 mm (Ronne and Joker 2006). This shows that the tree does well in hot dry climates with poor rainfall (Beau 2003).It is always found on deep sands with a 94–99% fine sand component (Graz 2007) and it is most frequent and occasionally dominant in Kalahari sand woodlands but is also found in munga woodland, scrub mopane and lake basin chipya.In core distribution areas it occurs in large grooves of open woodland  as a dominant or co-dominant tree species with other species like A.quanzensis and B.africana.The largest grooves can be 450 hactres and occur on sand crests, smaller ones are found where sand banks are against bedrock. It is also common on hummocks along alluvial margins of important water courses for example the Zambezi marshy. The tree does well on well drained deep sandy, sandy alluvium or rocky soils. It is rare on calcareous soils and does not do well on waterlogged, poorly drained or on soils subject to flooding (Agro forestry tree database).Its habitat is also subject to frequent fires (Graz 2007).

DESCRIPTION

The Schinziophyton Rautanenii tree is a dioecious shrub or small to medium-sized
tree up to 20 m tall (Graz 2207) and has a large straight trunk 1 metre in diameter
 with stubby and contorted branches and a large spreading crown (Beau 2003).The
 bark is up to 5 cm thick and is pale grey to light golden-brown , smooth first later
 becoming reticulate and flaky. Young branchlets, leaf buds and stalks have reddish brown furry hairs and both the branches and stems exude a white gum (Ronne and Joker 2006). The tap root goes down until it reaches water but the lateral root is very small (Beau 2003).




The Schinziophyton Rautanenii  tree (Ronne and Joker 2006)

  
The leaves are alternate, digitally compound, consisting of 5-7 leathery segments usually hairless below and with grey woolly hairs above. the leaves are also dark green on the upper side and creamy white on the underside (Agro forestry tree database 2009).The leaflet is also a wide lance to an egg shape. The leaflets are carried on hairy stalks that are up to 15cm in length and the leaves are also about 15cm long and there are usually 1 or 2 black glands on the upper side of each leaf-stalk (Beau 2003).
1, flowering twig; 2, part of male inflorescence; 3, female flower; 4, fruit, showing part of stone (Graz 2007)

The flowers are whitish yellow, dioecious, in loose rusty sprays. Inflorescence a terminal panicle and male flowers are in long rusty sprays while female flowers are shorter in length (Agro forestry tree database). Male inflorescence is 10–22 cm × 4–8 cm and female inflorescence is 5–6 cm × 2–3 cm. Male flowers have a pedicel 2–5 mm long, calyx lobes, 5 mm × 2–3 mm, and petals 6–7 mm × 2–3 mm. Female flowers have a pedicel 7–10 mm long, calyx lobes 8–9 mm × 5–6 mm, petals are 9 mm × 4 mm (Graz 2007).

The mongongo nuts (Ronne and Joker 2006)
Fruit is ovoid up to 3-5 cm × 2-3.5cm in diameter when dry and up to 7 × 5cm when fresh and consists of 5 layers; a light green fruit skin, a layer of fruit flesh, a thick and hard nut shell, a thinner woody inner shell and an edible nut (Leger 2003) weighing 7-10g with leathery skin and fleshy, dry, spongy pulp 2-5mm thick, shell tough 3-7mm thick. The stone contains 1 and occasionally 2 kernels. (Agro forestry tree database 2009).
The mongongo nut (Wikipedia 2009)
The fruit soft spongy pulp layer is about 20% of the fresh fruit (by volume), pleasantly aromatic and sweet at maturity. The skin takes up to 10% of the fruit by volume and the remaining 70% is the nut like seed, including the wide hard shell around it (Natural hub 2009).

GROWTH AND DEVELOPMENT
When the seed has germinated, the radicle grows slowly. When it is 5–10 cm long, 5–12 secondary roots emerge in a ring from immediately above the root-tip. When these roots are 20–50 mm long the plumule starts to emerge. The growth from seedling to sapling stage depends very much on the fire regime prevailing in the area. Fires reduce young saplings back to ground level as long as their bark is too thin to protect them (Graz 2007). The tree is deciduous and fruits after 15-25 years of growth but with irrigation they may start as early as after 4 years (Ronne and Joker 2006) and may live up to 100 years. From March to October the tree is leafless and it flowers from September to December (early summer) just before the beginning of the rains. Fruits develop from December to March and most fall off the tree from April to May and thereafter ripening continues on the ground (Agro forestry tree database 2009).   

USES
The fruit have been described as a “staple diet” in some areas especially among the San bushmen of Northern Botswana and Namibia (Wikipedia 2009).It is available the whole year and can be stored for a long time and even in those years when trees only bear fruits they still provide enough to keep people going. The fruit can be eaten fresh can be dried and is soaked in water and cooked, then mashed and eaten as a porridge. Alternatively it is fermented to give a refreshing potent beer or distilled for alcohol.      The nut is eaten together with the woody inner shell because it is difficult to remove the shell without wasting parts of the nut.
The nut consists of a white, very tasty and highly nutritious flesh. As the woody inner shell is uncomfortable to chew, the nut is mainly pounded in a mortar thereby reducing the shell to small piecies.This is then cooked together with meat and vegetables and eaten (Leger 2003).Fruit pulp and the seed meal which is rich in protein is fed to cattle, however the feed is suspected to cause a discolouration of beef.Widlife like elephants and Kudu feed on fruits (Agro forestry tree database 2009).
The kernel is rich in oil. The oil is used locally for cooking and for commercially for making soaps, varnishes, cosmetics, linoleum and oil cloth industry (Ronne and Joker 2006).Margarine has been made from the oil in Germany and England. The highly unsaturated oil may also serve well as paint medium for vanishing purposes. The oil from nuts has also been traditionally used as a body rub in the dry winter months to clean and moistern the skin (Agro forestry tree base 2009) and in cosmetics the oil is used for its hydrating and restructuring properties and ultra violet radiation protection for hair and skin (Graz 2007).
The wood being both strong  and light makes excellent fishing floats, insulating material, dart-boards, notice boards,masks,drums , temporary canoes and packing cases. The hollow trunks of the tree often form water reservoirs where rain water can be gathered. (Wikipedia 2009).Wood used as an insulating material and for constructing of crates and coffins. In Namibia the wood is also used for the construction of ox-drawn sledges that are used to transport goods in sandy areas. In Zambia the wood is used for carpentry and to make musical instruments, curios and toys, while the seeds are used in board games. The inner bark is used to make strings, for example for nets (Graz 2007).The branches are used as traditional fire sticks and truncheon cuttings are used for fencing. Roots control erosion as they protect sandy soils from wind and water erosion. The tree also provides shade and shelter in hot areas for example the Kalahari Desert and can be used for reclamation as it has potential use in desert encroachment prevention and sand dune stabilization (Agro forestry tree database 2009).The bark is used by women for straightening hair.
Medicinally the bark provides a cure for stomach and diarrhea.The middle red part of the bark is broken into pieces, put in cold water and cooked for up to 5-10minutes.The bark is removed after cooling down and the decortion is drunk. It is also a helpful drink for pregnant women who are feeling sick (Leger 2003).The roots are used as a remedy for stomach pains and the nuts are tied around ankles and are said to relieve leg pains (Agro forestry tree database 2009).

PROPERTIES
The nutritional composition of the fruit pulp per 100 g edible portion is: water 13.4 g, energy 1307 kJ (312 kcal), protein 6.6 g, fat 0.6 g, carbohydrate 70.2 g, fibre 3.5 g, Ca 89.6 mg, Mg 195 mg, P 46.0 mg, Fe 0.7 mg, Zn 1.4 mg, thiamine 0.28 mg, riboflavin 0.11 mg, niacin 0.12 mg, ascorbic acid 8.5 mg (Graz 2007). The kernel is 57g by weight fat. Of this about 43% are poly unsaturated fats (almost entirely linoleic acid), about 17% saturated fats (palmitic and stearic acid) and about 18% mono unsaturated fat (oleic) (Wikipedia 2009).The kernel also has per 100 g, water 4.8 g, energy 2685 kJ (641 kcal), protein 28.8 g, fat 57.3 g, carbohydrate 2.4 g, fibre 2.7 g, P 839 mg, niacin 0.42 mg(Graza 2007) and 193mg Ca, 527mg Mg, 3.7mg Fe, 2.8mg Cu, 4mg Zn, 0.3mg thiamine, 0.2mg riboflavin, o.3mg nicotinic acid, 565mg vitamin E ( almost entirely as y-tocopherol).Due to the very high y-tocopherol content, the oil is very stable and does not oxidise into “rancidity” for a very long time in spite of the high African heat (Natural hub 2009). Mungongo seeds oils from Zambian samples showed  a light yellow oil with refractive index of 1.4830, acid values 1.6%,  a peroxide value of 10 mg/kg and a solidification point of -7˚c, suggesting that this oil is rich in unsaturated fatty acids (Julian et al 2009).



SOWING AND GERMINATION
Propagation is mainly by seeds and seeds remain viable for up to 2 years when stored at 10˚c (Agro forestry tree database 2009).Germination is erratic and takes place over an extended period. Without pre-treatment a germination rate of 26% has been obtained. If the shell is removed prior to sowing the kernel is treated with ethylene the germination rate can reach 80% or more within 6 days. The rate of non surviving seedlings is high but once a seedling has been established it needs little attention. The seeds should be sown in sandy soil in half shade and the temperature kept above 7˚c.The seedlings very quickly develop deep roots ( Ronne and Joker 2006).

DORMANCY AND PRETREATMENT
A large number of the seeds remain dormant a year or more. The woody endocarp makes germination difficult and therefore needs to be removed or the end cut off to expose kernel before sowing. After shelling the seeds can be soaked in water for a week followed by storage under high temperature and humidity for 2 days in order to reach better germination. Alternately treatment of the kernels with either ethephon, ethylene or phosphonic acid can be done in order to speed up the germination process and rate (Ronne and Joker 2006).

DESEASES AND PESTS
Fallen fruits are attacked by moth and larvae which eventually eat all the fleshy parts. Timber is rapidly attacked by sap stain fungus, Ceratocystic maniliformis and elephants occasionally break branches of the tree reducing productivity (Agro forestry tree database 2009).The wood is not durable and susceptible to termite and lyctus attack (Graz 2007).

HARVESTING
The seeds are mature when the fruits have turned brown and soft and are shed while they are green (Ronne and Joker 2006).Since the fruit ripens on the ground they are simply picked up from under the trees. Harvesting starts at the end of the rainy season when fresh fruits have fallen. Gathering continues until the end of the dry season (September–November) when half of the fruits have already lost their pulp to insects. During the rainy season (November–March), when drinking water is found more easily, nuts are collected from more remote groves (Graz 2007).

YIELD
Fruit production is very closely linked to the amount of rain of the previous season, with crop yields higher in years following heavy rains. High rainfall after flowering has been found to damage the developing fruits, as do fires late in the dry season. Some estimates indicate yields of 200–1000 kg/ha in northern Namibia, and about 300 kg/ha in Angola (Graz 2007).Each female tree has around 950 fruit a year given sufficient rainy season. In a good year the seeds may be “knee deep” under the trees (Natural hub 2009). According to the extraction method and efficiency of unit of employed, yields of 28% of oil (traditional hand press) to 38% of oil (hydraulic press) can be achieved. In Zambia alone, the estimated production of about 3000 metric tonnes of seed would yield around 840 metric tonnes of oil. This represent a modest product supply for a niche oil product and simultaneously have a high impact for local and regional communities (Julian et al 2009).  

STORAGE AND VIABILITY
Seed is orthodox and should be stored at low moisture content in airtight containers. The seeds remain viable for up to 2 years if stored at 10˚c.In the seed bank at RBG kew, seed has been stored for 6 years at -20˚c maintaining a viability of 80% ( Ronne and Joker 2006)

MANAGEMENT
Once established the tree requires very little attention as it can withstand years of drought and has a few pests and disease incidence. Seed should be sown in sandy soil (Agro forestry tree database 2009).

GENETIC RESOURCES
The Tree Seed Centre of the Directorate of Forestry, Windhoek, Namibia has a comprehensive seed collection and as Schinziophyton rautanenii is widespread and is not damaged by the collection of fruits, it does not seem to be in danger of genetic erosion (Graz 2007).



PROSPECTS
Because of their local abundance, reliability of supply, ease of collection and good nutritional value, the kernels of Schinziophyton rautanenii remain an important traditional source of food in the Namib desert. The fruits are only collected from wild stands and it is unlikely that they will become important outside the area where they are used traditionally (Graz 2007).

DISCUSSION
The mongongo tree is distributed widely throughout southern Africa in the wild. The tree survives in low rainfall areas with poor soils where there is no crop production. As the tree grows in the wild it is not managed and so there are no production costs. The nuts are also available all year round and so provide a source of food and oil throughout the year. Both the fruit pulp and the kernel are highly nutritious and provide oil and are both used in food and industrial production of various products. The wood of the tree is also used to produce various wood products and various parts of the tree are used for medicinal purposes. The tree takes many years to bear fruit and its germination percentage is very low. It is also affected by a few pests and diseases.

CONCLUSION
The mongongo tree provides food in marginal areas where there is very little crop production. The oil is very nutritious and is used for cooking and in manufacturing of various products in industries. The oil however has a low keeping quality and so deteriorates rapidly. There is therefore potential for commercial production of oil from the mongongo nut.

RECCOMMENDATIONS
As the land where the mungongo trees are indigenous is not suitable for agricultural exploitation and all nuts are collected from the wild, the development of additional uses and external markets for this under recognized oilseed can benefit the rural communities and provide a new export product from Africa and a new ingredient for global cosmetic industry. However the keeping quality of oil should be improved and research should also be focussed on reducing the number of years for the tree to produce fruit which can enable it to be produced commercially.

REFERENCES
1.      Agro forestry Tree Database. A Tree Species Reference and Selection Guide.17 February 2009. http//www.worldagroforestrycentre.org.

2.      Beu M.2003 .The Mungongo: Manketti Nut. Natural food nuts uncommon.

3.      Graz F.P.2007.Schinziophyton rautanenii (schinz) Radd-sm.Prota 14: Vegetable oils.

4.      Julian H.R, Korach A.R, Simon J.E, and Wamulwange C. 18 February 2009.Mungongo Cold Pressed Oil (Schiniziophyton Rautanenni): A new Natural product with Potential cosmetic applications.ISHS Acta Horticulture 756. http://www.actahort.org.

5.      Leger S.2003. The Hidden Gifts of Nature.

6.      Natural hub.com. 17 February 2009. http://www.naturalhub.com.

7.      Ronne C and Joker D. April 2006.Seed Leaflet Number 114.Forest and Landscape Denmark.

Wikipedia.The free Encyclopedia.18 February 2009.http://en.wikipedia.org



MAIZE

MAIZE
Botanical name: Zea mays L.
Family: Graminae
Common name: Maize, corn
Chromosome number: 2n = 20
Chemical composition
         Composition of mature grain per 100g
-         Water 10,4 g
-         Energy 1527 kj
-         Protein 9,4g
-         Fat 4,7g
-         Carbohydrate 74,3g
-         Dietary fibre 7,3 g
-         Calcium 7mg
-         Phosphorus 210mg
-         Iron 2,7mg
-thiamin 0,39mg
-riboflavin 0,20mg
-niacin 3,6mg
-vitamin B6 0,62 mg
-folate 19μg
-ascorbic acid o mg
         Essential amino acids composition per 100g edible portion
-tryptophan 67mg
-lysine 265 mg
-methionine
-phenylalanine 463 mg
-threonine 354 mg
-valine 477mg
-leucine 1155mg
-isoleucine 337μg
         Principal fatty acids per 100g edible portion
-linoleic acid 2097mg
-oleic acid 1247mg
-palmitic acid 569mg
         Endosperm (80% of weight of grain)
-poor in ph and ca
-contains most of the starch and 2/3 of proteins
-75% amylopectin
-25% amylose
USES
         As food
-eaten fresh on the cob boiled or roasted
-seeds roasted
-grain ground or milled into mealie meal and made into porridge or papa which is eaten with vegetables or various stews
-mealie meal can be fermented into traditional beer
-baby cobs or baby corn (very young inflorescence) are vegetables especially in the western countries
-baking, snack foods
-breakfast cereals
-Ice-cream, frozen deserts
-jam, jellies
-meat products
-soups
-bread making
         Source of starch which is made into sugars such as dextrose and fructose which are used as artificial sweeteners, laundry starch,thickeners,hardeners of paper, glue
         Source of oil from the germ which is used for cooking, margarine,baking,soap,slads,glycerine
         Source of ethanol which may be added to petrol to produce a blended motor fuel
         Used to produce alcohol beverages
         Silage to feed livestock especially in western countries where special cvs and production technologies have been developed
         Green manure
         Cobs used as a source of fuel
         Stalk-fuel,fodder,thatching,compost
         Fibre in stems and inner leaves surrounding the cob are made into paper
         Residues from production of starch and oil are used as animal feed(corn gluten meal and corn gluten feed)
         Tyre production
         Compostable plastics, packaging films, fast food serving utensils manufactured with maize based polylactic acid
         Corn based polylactic acid can be blended with cotton, wool or silk to make exercise clothing,suits,carpets
         Pharmaceuticals
         Cob leaves used to wrap foods, made into cloth or mats, used for mattress filling
         Ash from burnt stem can be used as a substitute for salt
         In southern Africa the incinerated cob is included into snuff
Medicinal uses especially in African countries
         Urino genital problems are treated with prescriptions based on whole or parts of the maize plant especially a decoction of the styles
         Decoction of the styles also used to treat jaundice
         Fever is treated by drinking a leaf maceration
         Gonorrhea is treated by charcoal made from maize stalk
         Infusion from burnt cob is used to wash wounds
         Water obtained during the preparation of papa is used to soak bark or roots of some plants and this is used to treat fever or malaria
         In Nigeria whole dried maize fruit and dried yam with some charms are planted and buried together and this preparation is done to unite or bind couples together with the effect that they will never remarry
GROWTH AND DEVELOPMENT
         Climatic requirement
 -warm season plant
         Divisions of plant development

Vegetative
-each leaf stage is defined according to the uppermost leaf whose leaf collar is visible.
1. VE-emergence
-planted seed absorb water and begins growth radicle stars developing
2-3 days after planting followed by the coleoptile with the enclosed plumule (embryonic plant).
-Emergence is finally attained by rapid mesocotely elongation which pushes the growing coleoptile to the soil surface.
-under warm moist conditions emergence will occur within 4-5 days after planting but under cool or dry conditions it takes 2 weeks or longer.






-V3 leaf stage
-root hairs growing from the nodal roots by this time
-all leaves and ear shoots that the plant will eventually produce are being initiated at this stage.
-at about V5 leaf and ear shoot initiation will be complete and a microscopically small tassel is initiated in the stem apex.
-at this point the stem apex at tassel initiation is just under or at the soil surface although total above ground height is about 20cm.





V6 leaf stage
-the growing point and tassel are above the soil surface and the stalk begins to elongate.
-ear shoots or tillers which initially looked very similar are visible at this time.
-loss of the two lowest leaves may have already occurred by the V8 stage
V9 leaf stage
-ear shoots (potential) are visible upon dissection of a V9 plant.
-by V10, the time between the appearance of new leaf stages will shorten generally occurring every 2 to 3 days.





V12 leaf stage
-the number of ovules (potential kernels) on each ear and the size of the ear are determined at this stage
V17 leaf stage
-the tip of the tassel may also be visible at this stage
V18 leaf stage
-silks from the basal ear ovules are the first to elongate and those from the tip ovules are the last to elongate.
-brace roots (terminal aerial nodal roots) are now growing from the nodes above the soil surface.
-VT-tasselling stage
-initiated when the last branch of the tassel is completely visible and the silks have not yet emerged (are not visible)
-begins approximately 2-3 days before silk emergence during which time the corn plant will almost attain its full height and pollen shed begins





Reproductive stages
         R1 stage-silking
-begins when any silks are visible outside husks
-pollination when fallen pollen grains are caught by the silks
-a captured pollen grain takes about 24 hrs to grow down the silk to the ovule where fertilisation occurs and the ovule becomes a kernel
-2-3 days require for all silks on a single ear to be exposed and pollinated.

         R2-blister (10-14 days after silking)
-1st stage of grain filling
-immediately after pollination, the silk separates from the cob and the developing kernels look like a blister
-the content of the kernel is clear and jellylike
-white and yellow maize look the same at this stage
-kernels at the base of the cob develop1st and those at the tip develop last

         R3-milk(18-22 days after silking)
-         kernel displays yellow colour on the outside, and the inner fluid is now milky white due to accumulating starch.
-         Although initially slow to develop, the embryo is growing rapidly now and is easily seen upon dissection.
-          Most of the R3 kernel has grown out from the surrounding cob materials and the silks at this time are brown and dry or becoming dry.

         R4-dough (24-28 days after silking)
1.Soft dough stage
          -Kernel content is soft and sweet
          -kernels of yellow maize start to change colour
           -the end of this stage is ideal for picking for green maize
2.Hard dough stage
-moisture content of grain drops rapidly and kernel content changes to a paste
-formation of starch increases
-weight of the grain will be about half the actual yield

         R5-dent (35-42 days after silking)
-correct time to cut silage
-stage is complete when all kernels have formed a dent on the crown
-moisture content of grain decreases quickly to around 50%
  • Physiological maturity (55-65 days after silking)
-is reached when all kernels on the ear have attained their maximum dry weight or maximum dry weight or maximum dry matter accumulation
-black or brown abscission layer formed from the tip ear kernels to the basal kernels
-husks and many leaves may no longer be green although the stalk maybe
-colour of the husk leaves that cover the cob are 70 – 80% light brown
-MC of grain decrease from 50 to below 40%





SEED PRODUCTION
-seed grower must plant foundation seed of an approved cultivar
-the seed must be planted on clean ground free from weeds and should not have been planted to maize the previous year
-use herbicides and pesticides if necessary
-isolation of the seed producing field is required (at least 500m away)
-off-type plants should be removed
-field inspections should be made by representatives of the seed certifying agency to check the purity of the cultivar
-seed inspections necessary in harvesting, conditioning and other processing operations
-several insecticides and fungicides are used in treating seed to disinfect and disinfest them fro pathogenic organisms
-official tags supplied by seed certifying agency are sealed on the bags of seed approved for certification.
         Seed produced by seed companies like seed-co meet the following quality standards
-germination (min)-90%
-physical purity (min)-99%
-insect damaged seeds (max)-1,5%
-diseased seed (max)-0,75%
-total defects (max)-2%
-genetic purity (min)-95%
-2 types of maize seed, open pollinated (product of natural pollination) and hybrid seed (1st generation offspring of a cross between 2 individuals differing in 1 or more genes).

-smallholder farmers generally select seed from the next crop from the last harvest.
-selected cobs are stored at home in the surrounding leaves above the fireplace to prevent insect damage




SEED STORAGE
-MC of grain should be reduced to 12-15%
-seeds are considered to be in storage from the moment they reach physiological maturity until they germinate
1. the entire storage period can be divided into the following stages
2. storage on plants (physiological harvest until harvest)
3. Harvest until processed and stored
4. In transit (railway wargons, trucks, carts, railway sheds etc)
5. On the user’s farms
-with smallholder farmers shelled grain is dried for a few days and then stored in bags, tins or baskets
-farmers in Botswana use many traditional methods of storing seeds
-woven baskets, bins made from cow dung and wood ash, earthern pots, mud granaries
on large commercial scale grain is stored in bulk in
1. Grain bin storage
-grain stored in bins of different materials (concrete, steel, wood)
-maybe airtight or ventilated

2. Grain elevators
-large silo bins are constructed together to form a grain elevator
-usually constructed at railroad siding or water fronts to facilitate grain transportation
  • For commercial seed storage
1. Conditioned storage
-seeds maintained in a dry and cool environment and moisture content should be about 12-13% and 20˚c or less
-seed quality maintained for a year
2. Hermetic storage
-seeds sealed in moisture resistant containers
-metal containers are used when very long storage periods are desired.
-before sealing the ambient air in the container may be replaced with an inert gas (argon or nitrogen).
3. Containerized seed storage
-seeds are maintained in specially constructed rooms, equiped with dehumidifiers and other environmentally control systems
-sometimes a desiccant is used to control the level of humidity
PROCCESSING
  • Traditional Millstone for Grinding Maize
-Operating a millstone of this kind needs 2 - 3 people. It has a capacity to grind 4 - 5 kg of maize grains at one time. The maize flour is used for making various kinds of cake. Maize which is not so finely ground is eaten mixed with rice, beans and other foods. It is also used to make sweet soy sauce.

         Pedal-Driven Maize Grinder
-The weight and installation area of this machine are only 1/5 those of the millstone. Its structure is simple, and a man of average health can operate it .The operating capacity is the same as that of the millstone, and so is the production of maize flour.

         Improved Pan to Steam Maize
-This improved pan is made of cast iron. Inside the pan, there is an iron funnel which channels the steam into the maize flow, thus creating a kind of dough. Using the pan, each batch of maize requires only two hours to be steamed, and uses 40% less firewood than the conventional steamer.

         Cake Toasting Mold
-This iron mold can be used to press and toast various kinds of cake, made either from maize flour or from a mixture of maize and other flours, mixed with other ingredients and seasonings to make a high-value product. Toasted cakes can be eaten immediately, or preserved for later use.

         Small Mechanized Press
-One suitable press for farm households or small rural factories is the Eztrusion press. It has the capacity to process 20 - 25 kg of maize per hour. It is small, easy to operate and inexpensive. It gives a quick return on capital investment.


AGRONOMIC MANAGEMENT
         Temperature
-minimum temperature for germination 10˚c and 20˚c
-average daily temperature of at least 20˚c for adequate growth and development
-optimum temperature 25˚c-30˚c
-temperature above 35˚c reduces yields
-frost not tolerated
-at temperatures above 45˚c or below 6˚c photosynthesis comes to a stand still
-should receive the necessary heat units in order to complete growth and therefore develop from one stage to the next
-base temperature is 10˚c
         Water
-in the tropics maize does best with 600-900mm well distributed rainfall during the growing season.
-initially rainfall requirement is low but builds up to a maximum during the flowering period.
-thereafter the moisture requirement progressively decreases until the plants are physiologically mature
-critical stages of water requirement are seedling stage, knee-height stage, tasselling, silking and grain filling stages.
-moisture requirement is at its highest approximately 2 weeks before and after pollination as pollen is pure protein and thus require a lot of energy for its production
-water shortage for even 2 days of tasselling and silking can reduce maize yields to about 20% and 6-8 to about 50%.
-period of drought stress during vegetative stage results in smaller plants.
-a vigorous growing maize plant requires about 2-3 litres of water per day during peak growing period or an average consumptive use of water varies from 2,5 to 4,3mm per day.
-under high plant populations the requirement can be 10mm or more per day but is determined by prevailing temperatures, humidity and airflow.
-good moisture management is improved by ploughing in organic matter, breaking up any compaction layer and correct scheduling of irrigation.
-when irrigating irrigation should continue until 80% of all the outer cob leaves have turned brown.
-at this stage all cobs will be physiologically mature and no moisture is needed for grain filling.

SOILS
-can be grown on soils with pH of 5-8 but 5,5-7 is optimal
-does not tolerate water logging and is sensitive to salinity
-soils should allow optimum root development
-hybrids that can tolerate acid soils exist although no hybrid is resistant to soil acidity
-maize is best adapted to well drained sandy loam to silty loam soils
-will not thrive well on heavy clays
-the majority of tropical soils are acidic an aluminium toxicity is the most important reason for crop failure in such soils.
-on acid soils liming is important and can also supply the essential elements of ca and mg.




SOIL FERTILITY
-low fertility of most tropical soils reduces maize yields.
-maize responds well to fertilisers
-N is the most limiting nutrient in the tropics and provides the major difference between low and high input agriculture.
-N uptake is slow during the first month after planting but increases to a maximum during formation of the inflorescences.
-high nitrogen levels should be applied in 2 doses, the first dose at planting or 2 to3 weeks after emergence and the second one about 2 weeks before flowering.
Yield potential t/ha
2
3
4
5
6
7
8
9
10
Nitrogen potential kg/ha
20
45
70
95
120
145
170
195
220
(Pannar seed limited).
-the higher the yield target the more N per tonne of grain is required.
-Ph is the second most limiting and is immobilised by Al and Fe in acid soils and by Ca and Mg in calcareous soils.
-phosphate is not taken up easily by maize and many tropical soils are deficient in available phosphate.
-fertiliser is applied by band placement or broadcast with band being economical and efficient way of limiting fixation of nutrients.
-the exact amount of fertiliser that has to be applied to the soil will depend not only on the plant requirement of individual nutrients but also on how much of them the soil can supply.
--a general recommendation: apply 120kgN,60kg P2O5, and 40kg K2O per hectare for hybrids and 80kg N and 30kg P2O5 and 20kg K20 per hectare for composites.
-advisable to apply OM before ploughing to improve soil structure and supply nutrients.
-about 10-15 tonnes of well rotted OM in the form of farmyard manure or compost can be added before





Wkly requirements as % of total need
N%
Ph%
K%
Water %
EMERGENCE
LESS THAN 1
LESS THAN 1
LESS THAN 1
LESS THAN 1
1 WK
 1
2 WKS
1
2
3 WKS
2
1
 3
4
4 WKS
7
2
9
5
5 WKS
11
4
16
7
6 WKS
14
7
21
10
7 WKS
15
10
20
11
TASSELLING
16
11
13
12
SILKING
12
15
8
12
10 WKS
10
13
5
11
11 WKS
6
11
1
8
12 WKS
4
9
-K
6
13 WKS
2
8
-K
5
14 WKS
LESS THAN 1
5
-K
3
15 WKS
2
-K
2
16 WKS
1
-K
1
17 WKS
LESS THAN 1
-K
LESS THAN 1
MATURITY





 

ALTITUDES
-can be grown from lowland wet tropics to over 3500m altitude.
-found from sea level to 3700m above sea level from 55˚ N to 45˚S.
COMMON WEEDS
-Sensitive to weed competition during the 1st 4-6 weeks after emergence.
-in case the weeds are not controlled at the right time, there is 50-60 % reduction in yield.
-2 or 3 manual weedings needed.
-hand hoes, spades, cultivators
-cynodon dactylon, eluesine indica, sataria glauca, cyperus rotundus, sorghum halapense, commelina benghalensis, solanum nigrum, striga species (parasitic witch weed).
MAIZE DISEASES
-maize is subjected to as many as 112 diseases on a global basis
         Fungal
-stalk rots (diplodia maydis, erwinia caratova), leaf blights (bipolaris maydis), downy mildew (peronosclerospora sorghi), smut (ustilago maydis), rusts (puccinia sorghi), grey leaf spot (cercospora zeae maydis), diploid cobrot/stem rot (stenocarpilla maydis), giberella ear and stem rot (fusarium graminearum).
-can be controlled byfield sanitation, crop rotation, use of resistant varieties, destruction of plant debris by burning or deep ploughing, spraying fungicides and seed treatments with fungicides





                                            Fusarium cob rot

                                      Diplodia cob rot

common rust                                                                




                           leaf blight
  • bacterial diseases: bacterial stalk rots (erwinia species), bacterial leaf streak and spots (xanthomonas campestris), bacterial stripe (pseudomonas andropogonis).
-can be controlled by crop rotation, spraying, burying or burning debris
  • viral diseases-maize streak virus (MSV), maize dwarf virus(MDV), sugarcane mosaic virus (SCMV), maize chlorotic mottle virus (MCMV), guinea grass mosaic potyvirus (GGMV),maize eyespot virus (MESV), maize mosaic rhabdovirus (MMV), maize mottle/chlorotic stunt virus (MMGSV) and maize stripe tenuivirus (MStpv).
-can be controlled bydestorying alternative hosts of vectors, spraying chemicals for control of vectors and using resistant or tolerant varieties.
MAIZE NEMATODES
-root knot nematodes :( meloidogyne incognita, m.javanica, m.chitwoodi), lesion nematodes (pratylenchus penetrans, p.thornei, p.zeae), lance nematodes (hoplolaimus galeatus), stunt nematodes (tylenchorhynchus dubius), stubby root (paratrichodorus minor).
-can be controlled by crop rotation and trap crops and systematic insecticides.
MAIZE PESTS
-cutworms(agrotis sp), stembores and stalkbores(B.fusca, E.saccharina), cob borer(mussida nigrivenella), cotton bollworm(helicorvepa armigera),armyworm(helicorvepa armigera), leafhoppers (cicadulina sp),grasshoppers(zonocerus variegurus),wirewom ,stinkbug(E.servus), corn leaf aphid(R.maidis) and storage pests like grain moths(S.cereala), grain weevels(sitophilus sp), larger grain borer(P.trucutus).
-can be controlled by using resistant or tolerant varieties, trap crops, insecticides and use of natural enemies.

 
HARVESTING
-in general harvesting takes place 10-15 days after grain has reached physiological maturity (when the process of nutrient uptake into kernels is over).
-indication of maturity are yellowing of the leaves, yellow dry papery leaves around the cobs and hard grains with glassy surface resistant to scoring with the thumbnail and glassiness depending on variety.
-in the dry season maize is often left in the field until the moisture content has fallen to 15-20%.
1. Hand harvesting
-small scale farmers harvest by hand.
-to harvest maize by hand, the ears are pulled from the stalk of the plant and no tool is used.
-Indicatively, the average duration of a manual maize harvest varies from 120 to 200 man-hours ( 15-25 man-days) per hectare.
-shucking the ears, that is, the removal of the husks covering the ears, may be done by hand or by machine at the same time as the harvest.
-If this operation is done by hand, it requires about 130 man-hours (about 16 man-days) per hectare.
-hand harvesting of maize is considered practicable for crops of under 12 hectares, if climate and availability of labour permit
-The work capacity of these machines varies from 1.6 to 3.45 h/ha, with
75 to 80 percent of the ears completely shucked, and total grain losses lower than 4.5 percent.
-two operators - a driver and a worker - are generally necessary to run
these machines.  use of one-row corn-pickers is economically
advantageous for harvesting a minimum of 2530 hectares a year; for
two-row machines the minimum harvest should be 30-60 hectares.
-corn-shellers resemble corn-pickers but have a device for shelling and
cleaning grains. These machines can thus simultaneously harvest,
shuck and shell the ears and pre-clean the kernels.
-sometimes coupled to a trailer for transport of the harvested grains,
one- or two-row corn-shellers can be tractor-drawn or carried.
-the self-propelled type, capable of harvesting two, three, or four rows,
is, however, the most widespread, since its performance is superior to
that of the tractor-drawn models described above.
-the work capacity of these machines is comparable to that of corn-pickers,
with grain-losses lower than 3 or 4 percent.
-another machine that is capable of simultaneously harvesting, shucking,
shelling, and cleaning maize is the combine-harvester.
-this machine is derived from a combine-harvester for wheat on which
modifications have been made to the cutting apparatus and the threshing device.
-although the work capacity of these machines depends on harvesting
conditions and on the size and shape of the parcels, it can run from 0.8
to 1.2 h/ha for six-row machines processing the whole plant, and from
0.4 to 0.6 h/ha for six-row machines treating only the ears.
-overall grain losses, usually caused by the cutting device, are rarely higher than 3 percent.
-two operators are generally needed for these machines.
-the use of combine-harvesters, like that of corn-shellers, offers an economic advantage for harvests of a minimum of 40-75 hectares a year.

PRODUCTION AND TRADE
-according to FAO estimates, the average world production of maize from 1999-2003 amounted 611 million t/yr from 139 million hectares.
-leading producers of maize globally are
1.USA -243 million t/yr from 28million ha
2.China -117million t/yr from 24 million ha
3.Brazil -38 million t/yr from 12 million ha
4.Mexico -19 million t/yr from 7 million ha
5.France -15million t/yr from 2 million ha
6.Argentina -15 million t/yr from 3 million ha
 7. India -12 million t/yr from 7 million ha
8.South Africa -9,4 million t/yr from 3,6 million ha
-maize production from tropical Africa in 1999-2003 was 26,6 million t/yr from 21,1 million hectares.
-the main producing countries being
1.Nigeria -4,7 million t/yr from 4,2 million ha
2.Ethiopia -2,9 million t/yr from 1,6 million ha
3.Tanzania -2,6 million t/yr from 1,6 million ha
4.Kenya -2,5 million t/yr from 1,6 million ha
5.Malawi 2 million t/yr from 1,5 million ha
-from 1961 to 1965 to 1999-2003 the annual maize production in tropical Africa increased from 9,1 to 26,6 million t/yr and the harvested area from 10,2 to 21,2 million ha.
-average world export of maize amounted to 80,1 million t/yr in 1998-2002 with
1.USA -47,5 million t/yr
2.Argentina -10,3 million t/yr
3.France -7,9 million t/yr
4.China – 7,4 million t/yr as the main exporters
-exported maize from tropical Africa was only 307 000 t/yr with
1.Zimbabwe -143 000 t/yr
2.Tanzania – 42 000 t/yr
3.Uganda – 25 000 t/yr as the main exporters
-the main importers were
1.Japan – 16,3 million t/yr
2.South korea – 8,3 million t/yr
-maize importers into tropical Africa were 1,8 million t/yr
RESEARCH DONE ON MAIZE IN BOTSWANA
1. Department of agricultural research, Botswana
         phosphate and kraal manure experiment in Lobatse
-use of kraal manure alone was highly significant than mixture of kraal manure and P and P alone.
         Effect of seasonal rainfall on maize
-maize in Botswana is largely dependent upon rainfall received in february and march each year ie during flowering period
         Mahalapye spacing trials
-maize is best spaced at 30” intervals in rows 36” apart.
-in dry areas slightly wider spacing will give higher yields
         Nitrogen fertiliser experiment
-N in form of 100lbs of ammonium sulphate or as 1 ½ tonnes of kraal manure per acre gave significant increase in maize yields at Lobatse.
         Maize hybrid evaluation trial
-the grain yield recorded showed that some hybrids such as PNR 473, SNK 2154, PAN 6146, and PAN 6578 have good potential in Botswana under dryland farming.
         Early maturing experiments
-23 early maturing genotypes some regional and local check variety which was KEP.
-average yield shows that regional check R201 was superior to other genotypes with the average yield of 4684kg/ha.
         Intermediate to late maturing hybrids yield trials
-an open pollinated variety had the lowest yield when compared to the hybrids.
-KEP performed in a simillar manner to the hybrids
         Effect of timing and rate of Nitrogen supplied to maize in Pandamatenga vertisols
-maize grain yield was significantly increased by Nitrogen application while splitting the applied Nitrogen increased Yields by 17%.
         Green mealies
-4 green mealies variety trials were conducted at Sebele and Bobonong
-R201,PNR 473,produced the highest yields while other varieties produced lower but similar yields
-varieties R 01,TX 9, AX 305W, SNK 2151 and A1257N produced larger cobs while SNK 220 produced the smallest cobs
         Control of maize stalk borer (insect control trial)
-carbofuran provided the most satisfactory control of stalkborer than trichlorfon and carbaryl but all the insecticides were found to have brought about significant reduction in stalkborers
         Effect of tie-ridging and manure on yield of maize
-tie-ridging and manure did not improvr maize yields
-plant stand at harvest revealed that adding no manure and tie-ridging increased plant stand
         Effect of variety and plant population on yield of maize
-KEP*PHIJ-6-94, KEP*PHEB-7-94 were compared with KEP in various plant population
-no significant difference in yield
-plant variety interaction was not significant
  -KEP responded well to recommended plant population of 65000 plants per hectare compared to 40000 plants.

WHAT NEEDS TO BE DONE
-Nitrogen fixation in maize and increased N capture by roots
-improved P use efficiency and tolerance to acid soils
-tolerance to salinity.
-recover from water stress once water is available
-increase the efficiency with which the plant partitions photosynthates to the grain while keeping the biomass unchanged. This can be done by reducing plant height/size through use of dwarfing genes. can also be done by producing early flowering cultivars coupled with fert, pest control and irrigation which allows the plant to allocate assimilates to seeds sooner thereby leading to reduced accumulation of reserves in leaves.
-increase photosynthetic efficiency by eliminating the limiting factors of photosynthesis which are low sunlight interception, water stress, pest and weeds by leaf orientation and breeding for drought and pest and weed tolerant cultivars
-more water use efficiency to produce more yield with minimal rainfall
-shorter lifecycle in order to produce grain before rains are scarce
-resistance or adaptation or tolerance to heat.
MAIZE POTENTIAL IN BOTSWANA
-maize is a staple food in Botswana
-one of the main sources of energy
-give the highest yield per man hour invested as compared to other cereals.
-first crop to be harvested for food during the hunger period especially as green mealies.
-easy to grow as a sole crop or intercropped with other crops
-east to harvest
-does not shatter and is not liable to bird damage
-many uses as food(papa,porridge,roasted) and in industries
-source of income for smallholder farmers and traders

 
-maize imports are increasing which shows a growing demand for maize and its products.
-shows that local production is not meeting the population demand for maize.
-production fluctuates according to seasons/yrs and this goes hand in hand with the area harvested.
-yield/ha is constant
-maybe caused by farmers still using substandard traditional ways of production like
-little or no use of fertilisers, no use of herbicides or pesticides, no
irrigation since water is a limiting factor, use of varieties which are not
high yielding under semi arid conditions.
-lack of technologies as many maize technologies have been developed in national and international research stations in Africa but most of these are not yet adopted by farmers.
-short supply of high quality seeds because of lack of
-as demand is increasing and yield/ha is not increasing, there is need to increase yield in order to reduce the amount of imported maize and so reducing total expenditure.
-this can be done by
-farmers improving access and use of fertilisers and crop protection chemicals-herbicides and pesticides.
-using cultivars and cropping techniques that fit well into prevailing cropping systems.
-having farmers shifting from small scale to large scale production where the benefits of irrigation and adopting high technologies are high
-use of high breeds that tolerate to a greater extend the adverse effects of heat and drought stress.
-eliminating gaps between researchers and farmers so that research results are conveyed to farmers







REFERENCES
1.Acquaah, G.2002.Principles of crop production,Theory,techniques and technology.Pentice hall
2. Badu-Apraku, B. & Fakorede, M.A.B., 2006. Zea mays L. [Internet] Record from Protabase. Brink, M. & Belay, G. (Editors). PROTA (Plant Resources of Tropical Africa ), Wageningen, Netherlands. < http://database.prota.org/search.htm>. Accessed 24 March 2009
3.Bell, R.A.2005.Insect pests of Kwazulu Natal.www.africanagriculture.com.Accesssed 03 March 2009.
4. Bessin, R. 1994. Armyworms in corn. Dept. of  Entomology, University of Kentucky, Lexington, KY. http://www.uky.edu/Agriculture/Entomology/entfacts/fldcrops/ef109.htm Accessed 03 March 2009.
5.Bijlmakers,H.1989.Insect pests of cereals in Ethiopia.Crop Production Phase 11.www.bijlemakers.com.Accessed 09 March 2009.
6. Center for Integrated Pest Management. 1982.  Insect and Related Pests of Field Crops (AG271), Pests of Corn/Sorghum. Armyworm/Corn Root Aphid/Corn Leaf Aphid/Stalk Borers. North Carolina State University. Raleigh, NC.http://ipmwww.nsu.edu/AG271/corn.html.Accessed 11 March 2009.
7. Clemson University. CE Sheets. Corn Insects. Southern cornstalk borer. Department of Entomology, Clemson, S.C.http://entwebclemson edu/cesheets/com.Accessed 03 March 2009.
8.Chuanyan, Z.and Zhongren, N.2007.Estimating water needs of maize.African Journal of Agric Research,Vol 2,pp325-333.
9. Dicke, F. F. 1997. The most important corn insects. In Sprague, G. F (ed.) Corn and Corn  Improvement. American Society of Agronomy, Madison, WI.
10.Foster,J.E.2002.Maize insect pests in North America.IPM World Textbook.University of Minnesota,USA.
11.FAO Corporate Document Repository. Agricultural Engineering in development-Post harvest operation.www.fao.org.Accessed 18 March 2009.
12.Hill,J.H.2007.Corn development. Iowa State University,USA.
13.Ikasan.Crop Information.www.ikasan.org.Accessed 18 March 2009.
14.Institute of Plant Diseases and plant protection. 2005.University of Hannover,Germany.
15. Kulp, K. & Ponte, J.G. (Editors), 2000. Handbook of cereal science and technology. 2nd Edition.
     Marcel Dekker, New York, United States. 790 pp.
16.Kenyan Agricultural Research station. New Varieties released.africanagriculture.blogspot.com.Accessed 20 March 2009.
17. Kling, J.G. & Edmeades, G., 1997. Morphology and growth of maize. 2nd Edition. IITA/CIMMYT Research Guide No 9. IITA, Ibadan, Nigeria. 36 pp.
18. Landis, D. and B. Giebink. 1994.  Managing Soil Insects in Corn.  Extension Bulletin E-2267. Department of Entomology and Pesticide Research Center, Michigan State University, Lansing, MI.http://www.ent.msu.edu/cgi-bin/ipmfacts.pl?action=article&article=2267.tx
19. Lyon, W. F. and R. N. Williams.  Sap beetles. Ohio State University Extension Fact Sheet, HYG-2047-97, Columbus, OH.
20.Maize breeders Network(MBNET).www.africancrops.com.Accessed 20 March 2009.
21.Ministry of Agriculture.Department of Research.1985-2000.Annual Reports for Crop ResearchDivision.
22.Ministry of Agriculture and Rural Development,Vietnam.2007.Maize Proccessing by Fram households.
23.National centre for Biotechnology Education.1998.www.ncbe.gmfood/maize.Accessed o4 March 2009.
24. National Corn Growers Association. 1999. The World of Corn: Corn Production in the U.S. and Corn Crop Value.
URL=http://www.ncga.com/03world/main/index.html .
25.Nielsen,R.L.B.2003.Maize:New uses for an old crop.Agronomy Department,Purdue University,Indiana,USA.
26. Pierre, W. H., S. R. Aldrich and W. P. Martin. 1967. Advances in Corn Production: Principles and Practices. Iowa State University Press, Ames, Iowa.
27. Ritchie, S. W., J. J. Hanway, G. 0. Benson and J. C. Herman. 1992. How a Corn Plant Develops, Special Report No. 48. Iowa State University of Science and Technology, Cooperative Extension Service,  Ames, IA.
URL= http://www.ag.iastate.edu/departments/agronomy/corngrows.html#
28. Ristanovic, D., 2001. Maize. Crop production in tropical Africa. DGIC (Directorate General for International Coöperation), Ministry of Foreign Affairs, External Trade and International Coöperation, Brussels, Belgium. pp. 23–45
29.Seed co company limited.Maize varieties in Zimbabwe.www.africancrops.comAccessed 17March 2009.
30.Sparks,D.L.Advances in Agronomy. 1992.Academic press.
31. Smith, C.W., Betrán, J. and Runge, E.C.A.  2004. Corn: origin, history, technology, and production. John Wiley & Sons, Hoboken, New Jersey, United States.
32.Statistics on cereals in Botswana.www.fao.org.Accessed 17 March 2009.
33.Thottappidly, G and Rossel H.W.1993.Viruses and Virus Diseases of Maize in Tropical Africa.Plant Pathology 42,494-509.
34.Wikepedia ,the free encyclopedia.List of Maize diseases.wikepedia.co.Accessed 03 March 2009
35. Wilmarie, K.Pannar Quality seeds Limited.www.africancrops.com.Accessed 17 March 2009.