Knowledge of the botany and physiology of the maize plant and the implications for seed production

1. Anatomy and physiology ofAnatomy and physiology of
maize – Implications formaize – Implications for
quality maize seedquality maize seed
productionproduction
M.A.B. Fakorede & S.K Meseka

2. Brief description –Brief description –
Knowledge of the botany and physiology of
the maize plant and the implications for
seed production.

3. Outline of presentationOutline of presentation
Origin of maize
Morphology of the maize plant
Germination and emergence
Seedling and vegetative development
Reproductive phase
Implications on good quality seed production

4. Origin of maizeOrigin of maize
Botanical name: Zea mays L.
Family name: Poaceae (Gramineae)
Chromosome number: 2n = 20
Vernacular names: Maize, corn, Indian corn
(En). Maïs (Fr). Masara (Hausa), Aburoo
(Akan); Agbado (Yor); Oka (Ibo)

5. Origin of maizeOrigin of maize –– cont’dcont’d
Controversial; 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.

6. 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.

7. 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.

8. 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.

9. 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

10. 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.

11. Morphology –Morphology – Cont’dCont’d

12. Morphology –Morphology – Cont’dCont’d

13. Morphology –Morphology – Cont’dCont’d
Produces 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

14. Morphology –Morphology – Cont’dCont’d
Breeders 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

15. Morphology –Morphology – Cont’dCont’d
The Root
Maize 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.

16. Morphology –Morphology – Cont’dCont’d

17. 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.

18. Morphology –Morphology – Cont’dCont’d

19. 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.

20. 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.

21. 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.

22. Morphology –Morphology – Cont’dCont’d
The 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.

23. 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").

24. 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.

25. MorphologyMorphology –– Cont’dCont’d
Strongly 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

26. 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 factors
Does not travel far, but light enough to be
dispersed by the wind

27. Morphology –Morphology – Cont’dCont’d

28. Morphology –Morphology – Cont’dCont’d
 The Silk
One silk per ovule
Up to 45 cm long
Receptive throughout its length, but once pollinated,
no longer receptive
Silks for the ovules at the base of the ear grow first,
those for the tip grow last
Re-grows if cut back
May be up to 1000 per ear
Extrusion spread over several days
Highly sensitive to environmental factors, temperature
and moisture stresses in particular

29. Morphology –Morphology – Cont’dCont’d

30. Morphology –Morphology – Cont’dCont’d
The seed

31. Morphology –Morphology – Cont’dCont’d
The Seed
Maize 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

32. 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).

33. 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.

34. 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)

35. Grain-filling stages in maizeGrain-filling stages in maize

36. Physiological maturity indicatorsPhysiological maturity indicators
• Physiological maturity indicated by:-
Appearance of Brown or Black layer
Disappearance of milk line
Maximum dry matter accumulation in the seed
Kernel moisture content
• Seed germination occurs even prior to PM
• Attack by field-to-store pests and disease
organisms starts

37. Anatomy of maize seedAnatomy of maize seed
Maize seed - Longitudinal section

38. Implication in seed productionImplication in seed production
Easy 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

39. 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

40. 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

41. 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.

42. Maize growth stagesMaize growth stages –– Cont’dCont’d
For 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.

43. Maize growth stagesMaize growth stages –– Cont’dCont’d
The 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).

44. 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

45. Maize growth stages –Maize growth stages – Cont’dCont’d

46. Maize growth stages –Maize growth stages – Cont’dCont’d
Emergence = VE

47. Maize growth stages –Maize growth stages – Cont’dCont’d
Three collars = V3
Vegetative 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.

48. Maize growth stages –Maize growth stages – Cont’dCont’d
Silk 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.

49. Experimental evidenceExperimental evidence
VE 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.

50. Experimental evidenceExperimental evidence
Embryonic 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.

51. Experimental evidenceExperimental evidence
Vegetative stage
 Almost all pest & weed management decisions for
corn are based on the vegetative stage

52. 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

53. 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.

54. Effects of weed density on some quality attributes ofEffects of weed density on some quality attributes of
maize seedmaize seed
97
91 90 89
80
0
20
40
60
80
100
120
0 1 3 4 6
Weed density per maize plant
%Normalseedling
0
1
2
3
4
5
6
7
8
0 1 3 4 6
Weed density per maize plant
%Normalorabnormal
%Abnormal
%Dead
92
80 79 78 76
0
10
20
30
40
50
60
70
80
90
100
0 1 3 4 6
Weed density per maize plant
Emergence%
15
18 18
19
20
0
5
10
15
20
25
0 1 3 4 6
Weed density per maize plant
Emergencerate,days

55. ConclusionConclusion
Botanically, 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

56. ConclusionConclusion –– Cont’dCont’d
Similarly, 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.