anatomy and physiology of maize - implications for quality maize seed production
TRANSCRIPT
Anatomy and physiology Anatomy and physiology of maize – Implications for of maize – Implications for
quality maize seed quality maize seed productionproduction
M.A.B. Fakorede & S.K Meseka
Brief description – Brief description – Knowledge of the botany and physiology of the maize plant and the implications for seed production.
Outline of presentationOutline of presentationOrigin of maizeMorphology of the maize plantGermination and emergenceSeedling and vegetative developmentReproductive phaseImplications on good quality seed production
Origin of maizeOrigin of maizeBotanical name: Zea mays L.Family name: Poaceae (Gramineae)Chromosome number: 2n = 20Vernacular names: Maize, corn, Indian corn
(En). Maïs (Fr). Masara (Hausa), Aburoo (Akan); Agbado (Yor); Oka (Ibo)
Origin of maize Origin of maize – – cont’dcont’dControversial; three major theories propounded
(Anderson, 1945; Mangelsdorf & Reeves, 1959; Galinat, 1988)
However, Galinat (1988) which cited Mexico as probable origin of maize has gained much support
Maize originated through domestication of the wild grass teosinte (Zea mexicana), which is native to Mexico, Guatemala and Honduras.
Origin of maizeOrigin of maize – – cont’dcont’d• Maize was domesticated in southern Mexico
around 4000 B.C. • Early civilizations of the Americas depended on
maize cultivation. • Reported for the first time in West Africa in
1498, six years after Columbus discovered the West Indies.
Origin of maizeOrigin of maize – – cont’dcont’d• The Portuguese brought floury grain types from
Central and South America to São Tomé, from where they spread to the West African coast.
• By means of the trans-Saharan trade, the Arabs introduced the flinty types through northern Africa into sub-Saharan Africa.
• The flinty types still predominate in northern parts of
West Africa while the floury types prevail in the southern parts, with some variation from this pattern.
Origin of maizeOrigin of maize – – cont’dcont’d• Maize is grown from latitude 58°N in Canada and
Russia, throughout the tropics, to latitude 42°S in New Zealand and South America.
• Also grown in areas below sea level in the Caspian Plain up to areas as high as 3800 m in the Andean mountains (Bolivia and Peru).
• It is grown in all countries of Africa, from the coast through savanna regions to the semi-arid regions of West Africa, and from sea level to the mid- and high-altitudes of East and Central Africa.
• Maize is not known from the wild.
DefinitionsDefinitions
• Anatomy – the scientific study of the structure of the body and the relation of its parts
• Morphology – external features of an object
• Physiology – the science that studies the way the bodies of living things work
MorphologyMorphology
The Plant
Maize is a tall, determinate annual plant producing large, narrow, opposing leaves (about a tenth as wide as they are long), borne alternately along the length of a solid stem.
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’dProduces grains on lateral branches – cob
Many types, cultivars can be divided into 7 types (or cultivar groups) according to the structure and shape of the grain: Dent, Flint, Pod, Popcorn, Floury, Sweet, & Waxy
Cultivars can also be classified according to the maturity:
Extra-early, Early, Intermediate, Late, Extra-late
Morphology – Morphology – Cont’dCont’dBreeders also classify cultivars on the basis of their genetic constitution: Open-pollinated (OPVs or composites) - the more traditional germplasm such as Synthetics, EVs, Local
Hybrids – cultivars in which the F1 populations produced by crossing inbred parents are used to produce the commercial crop:
Single-cross, Three-way cross, Double-cross, &Top-cross
Morphology – Morphology – Cont’dCont’d
The RootMaize has three types of roots:-Seminal roots - which develop from radicle and
persist for long period; Adventitious/fibrous roots which are the effective
and active roots of plant ; Brace or prop roots, produced by lower two nodes.
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’d
A: Embryonic primary and seminal roots and postembryonic lateral and crown roots are already visible in 14-day-old maize seedlings.
B: Aboveground shoot-borne brace roots at
6-week after planting.
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’d
• The roots of the maize plant grow very rapidly and almost equally outwards and downwards.
• Favorable soils may allow corn root growth up to 60 cm laterally and in depth.
Morphology – Morphology – Cont’dCont’d
Stem• The stem generally attains a thickness of
three to four centimeters.
• The inter nodes are short and fairly thick at the base of the plant, become longer and thicker higher up the stem, and then taper again.
Morphology – Morphology – Cont’dCont’d
• The ear bearing inter node is longitudinally grooved, to allow proper positioning of the ear head (cob).
• The upper leaves in corn are more responsible for light interception and are major contributors of photosynthate to grain.
Morphology – Morphology – Cont’dCont’dThe Flower• Monoecious – Male and female flowers are
conspicuously located separately on same plant
Male inflorescences (tassels): are borne at the stem apex
Female inflorescences (ears): are borne at the apex of condensed, lateral branches protruding from leaf axils.
Morphology – Morphology – Cont’dCont’d
The male (staminate) inflorescence, a loose panicle, produces pairs of free spikelets each enclosing a fertile and a sterile floret.
The female (pistillate) inflorescence, a spike,
produces pairs of spikelets on the surface of a highly condensed rachis (central axis, or "cob").
Morphology – Morphology – Cont’dCont’d
• Each of the female spikelets encloses two fertile florets, one of whose ovaries will mature into a maize kernel once sexually fertilized by wind-blown pollen.
MorphologyMorphology – – Cont’dCont’dStrongly protandrous; male matures a few days
before the female; male located higher than female; apical dominance
Female flower about the middle of the plant, could be about 1-3, normally attached to leaf axils
Cross-pollinating, inbreeding detrimental
Morphology – Morphology – Cont’dCont’d
The Pollen Short-lived (12 – 24)Abundant (1,000,000 – 2,600,000/tassel)Sheds for several days (7 – 9 days)Affected by environmental factorsDoes not travel far, but light enough to be
dispersed by the wind
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’d The Silk
One silk per ovuleUp to 45 cm longReceptive throughout its length, but once pollinated,
no longer receptiveSilks for the ovules at the base of the ear grow first,
those for the tip grow lastRe-grows if cut backMay be up to 1000 per earExtrusion spread over several daysHighly sensitive to environmental factors, temperature
and moisture stresses in particular
Morphology – Morphology – Cont’dCont’d
Morphology – Morphology – Cont’dCont’dThe SeedMaize seed (grain) is botanically a caryopsis, a dry
fruit containing a single seed fused to the inner tissues of the fruit
The seed contains two sister structures - a germ (embryo) an endosperm which provides nutrients for the seedling until the seedling establishes sufficient leaf area to become autotrophy
Morphology – Morphology – Cont’dCont’d
The germ consists of a miniature plant axis, including approximately five embryonic leaves, a radicle, from which the root system will develop, and an attached seed leaf (scutellum).
The germ is the source of maize "vegetable oil" (total oil content of maize grain is 4% by weight).
Morphology – Morphology – Cont’dCont’d
The endosperm occupies about two thirds of a maize kernel's volume and accounts for approximately 86% of its dry weight.
The primary component of endosperm is starch, together with 10% bound protein (gluten), and this stored starch is the basis of the maize kernel's nutritional uses.
Morphology – Morphology – Cont’dCont’d
Whole, ground maize meal has an energetic value of 3,578 calories per kilogram.
Seed development has three Phases:-Lag Phase (high moisture content)Linear Phase Physiological Maturity Phase (high dry matter)
Grain-filling stages in maize Grain-filling stages in maize
Physiological maturity indicatorsPhysiological maturity indicators• Physiological maturity indicated by:-
Appearance of Brown or Black layerDisappearance of milk lineMaximum dry matter accumulation in the seedKernel moisture content
• Seed germination occurs even prior to PM
• Attack by field-to-store pests and disease organisms starts
Anatomy of maize seedAnatomy of maize seedMaize seed - Longitudinal section
Implication in seed productionImplication in seed productionEasy to self and/or cross-pollinate
Large number of seed from one pollination
Different family types may be produced; important to the breeder
Detasseling easily accomplished – important in commercial production of hybrids
Implication in seed productionImplication in seed production –Cont. –Cont. ASI increases chances of random mating – important
in maintaining Hardy-Weinberg equilibrium in OPVs
Controlled synchronization of male and female flowers possible – important in hybrid production
Maize populations characterized by heterozygosity, heterogeneity, enforced hybridization, depressed vigor when inbreeding is enforced
Implication in seed production – Cont.Implication in seed production – Cont.Timely harvesting – very important
Need for re-definition of PM now an on-going debate in the international scientific community
For example, Ajayi & Fakorede (1999) – maize seeds harvested long before PM were as viable and vigorous as those harvested at and after PM
Maize growth stagesMaize growth stages Typical corn plants develop 20 to 21 total leaves,
silk about 65 days after emergence, and mature around 110-125 days after emergence (maturity)
The specific time interval, however, can vary among
genotypes, environments, planting date, and location
The length of time between each growth stage,
therefore, is dependent upon these factors.
Maize growth stages Maize growth stages – – Cont’dCont’dFor example, an early maturing variety or hybrid
may produce fewer leaves or progress through the different growth stages at a faster rate than described here
In contrast, a late-maturity variety or hybrid may develop more leaves and progress through each growth stage at a slower pace.
Maize growth stagesMaize growth stages – – Cont’dCont’dThe staging system divides corn development
into vegetative (V) and reproductive (R) stages.
V stages are designated VE (emergence), Vn, where n represents the emerging leaf's order number, and VT (tasseling).
Maize growth stagesMaize growth stages – – Cont’dCont’d The reproductive phase has been divided
into seven stages as follows:- R0 – Anthesis - about 57 DAP R1 – Silk extrusion – 59 DAP
.
.
.
. R6 – Physiological maturity -112 DAP
Maize growth stages – Maize growth stages – Cont’dCont’d
Maize growth stages – Maize growth stages – Cont’dCont’dEmergence = VE
Maize growth stages – Maize growth stages – Cont’dCont’d Three collars = V3Vegetative stages are identified by the number of collars present on the corn plant. The leaf collar is the light-colored band at the base of an exposed leaf blade, near the spot where the leaf blade comes in contact with the stem.
Maize growth stages – Maize growth stages – Cont’dCont’dSilk extrusion = R1
Environmental stress at this time is detrimental to pollination and seed set, with moisture stress causing desiccation of silks and pollen grains.
Nutrient concentrations in the plant
are highly correlated with final grain yield.
Nitrogen and phosphorous uptake are rapid.
Experimental evidenceExperimental evidenceVE to V2
Coleoptile reaches the soil surface and exposure to sunlight causes elongation of the coleoptile and mesocotyl to stop
The growing point, located just above the
mesocotyl, is about 2 cm (0.75 in) below the soil surface.
Experimental evidenceExperimental evidenceEmbryonic leaves rapidly develop and grow
through the coleoptilar tip Seminal root growth begins to slow and nodal
roots are initiated at the crown
Delayed weed control at this stage will result in little yield loss, but late-emerging weeds may produce substantial seed, increasing the soil seed bank.
Experimental evidenceExperimental evidenceVegetative stage Almost all pest & weed management decisions for corn are based on the vegetative stage
VE - EVE - Emergencemergence Coleoptile reaches the soil surface and
exposure to sunlight causes elongation of the coleoptile and mesocotyl to stop. The growing point, located just above the mesocotyl, is about 2 cm (0.75 in) below the soil surface.
Embryonic leaves rapidly develop and grow through the coleoptilar tip.
Seminal root growth begins to slow and nodal roots are initiated at the crown.
5 DAP
V1 – First leaf collarV1 – First leaf collar Lowermost leaf (short with
rounded tip) has a visible leaf collar.
Nodal roots begin elongation.
Again, weed control at this growth stage will result in little yield loss, but seed from weeds that emerge later in the growing season may contribute to the soil seed bank if a residual herbicide has not been applied.
Effects of weed density on some quality attributes of Effects of weed density on some quality attributes of maize seedmaize seed
9791 90 89
80
0
20
40
60
80
100
120
0 1 3 4 6
Weed density per maize plant
% N
orm
al s
eedl
ing
0
1
2
3
4
5
6
7
8
0 1 3 4 6
Weed density per maize plant
%N
orm
al o
r abn
orm
al
%Abnormal
%Dead
92
80 79 78 76
0102030405060708090
100
0 1 3 4 6
Weed density per maize plant
Emer
genc
e %
15
18 1819 20
0
5
10
15
20
25
0 1 3 4 6
Weed density per maize plant
Emer
genc
e ra
te, d
ays
ConclusionConclusionBotanically, maize is highly vulnerable to genetic
contamination during the different stages of the seed multiplication chain
Theoretical considerations showed that genetic contamination during seed multiplication can be minimized by:- increasing the effective population size keeping strictly to the recommended isolation distance rouging volunteer and off-type plants thorough detasseling of the female parent in hybrid
maize seed production
ConclusionConclusion – – Cont’dCont’dSimilarly, maize seed production in developing
countries is vulnerable to physical contamination, along with attack by many field and storage pests
Adoption of recommended agronomic, quality assurance and storage practices will minimize physical contamination, pest attack and deterioration of maize seed in storage.
