Thursday Lecture – Corn
Reading: Textbook, Chapter 5
Reminder: Exam I - Tuesday
2/22
From Wall Street Journal
Quiz
1. Flour is ground-up ________________ (part of grain)
2. Name an Old World Cereal crop:
A New World Cereal crop:
Sorghum Likes it Hot and Dry
Origin: Ethiopia
Main Types of Sorghum
Four main types:
- grain sorghums
- sweet sorghum (animal feed)
- Sudan grass (related species)
- broomcorn
See Fig. 5.22, 5.24,
p. 125
Millets – A Mixed Bag
See Table 5.4, p. 126
Finger millet –
Eleusine coracana
Pearl millet –
Pennisetum glaucum
Maize – The New World Cereal
Origin: Mexico
Early Spread: Through New World
Maize – The New World Cereal
Origin: Mexico
Early Spread: Through New World
Note on the name:
Corn = small vegetables (barley, peas, lentils)
Maize = from Carib word (spanish mais)
The Corn Plant
See Fig. 5.26, p. 127
Corn Flowers
Corn Flowers, closer up
See Fig. 5.26, p. 127
The Corn Fruit
Evolution of Corn
See Fig. 5.28, p. 130
Teosinte
Corn Relatives
Zea diploperennis
Wild Ancestor of Corn:
Teosinte
• Structure of Maize:
grass, has terminal
staminate inflorescence
(=tassels) and lateral
pistillate inflorescence
(=ear; silks = styles)
Wild Ancestor of Corn:
Teosinte
• Structure of Maize:
grass, has terminal
staminate inflorescence
(=tassels) and lateral
pistillate inflorescence
(=ear; silks = styles)
Changes from Teosinte to Corn
Teosinte  Corn
See Fig. 5.28, 5.30,
p. 130, 132
1. Non-shattering pistillate inflorescence (cob)
2. Corn grains open, glumes soft
3. Cupule with 2 fertile spikelets, not one
4. Cupules 4-10 ranked, not 2-ranked
5. Corn – primary branches short, with pistillate ear
Changes were thought to be controlled by single gene changes
(analysis of 50,000 segregating progeny)
More recently, shown to be somewhat more complicated
Early development of corn
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
See Fig. 5.29, p. 131
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
2. Dent corn (soft center)
See Fig. 5.29, p. 131
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
2. Dent corn (soft center)
3. Flint corn (all hard)
See Fig. 5.29, p. 131
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
2. Dent corn (soft center)
3. Flint corn (all hard)
4. Popcorn (core of soft)
See Fig. 5.29, p. 131
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
2. Dent corn (soft center)
3. Flint corn (all hard)
4. Popcorn (core of soft)
5. Flour corn (all soft)
See Fig. 5.29, p. 131
Types of Corn
Differences: mainly related
to types of starch (hard vs.
soft) in grain.
1. Pod corn (husklike glumes)
2. Dent corn (soft center)
3. Flint corn (all hard)
4. Popcorn (core of soft)
5. Flour corn (all soft)
6. Sweet corn (sugars remain)
See Fig. 5.29, p. 131
Breeding of Maize
• traditionally, bred by selection - look for plants in population that
have desirable traits, save seeds, and then cultivate these for next
generation.
Breeding of Maize
• traditionally, bred by selection - look for plants in population that
have desirable traits, save seeds, and then cultivate these for next
generation.
Hybrid Corn
• Start with inbreeding  initially produce weaker plants
“inbreeding depression”
Breeding of Maize
• traditionally, bred by selection - look for plants in population that
have desirable traits, save seeds, and then cultivate these for next
generation.
Hybrid Corn
• Start with inbreeding  initially produce weaker plants
“inbreeding depression”
• Cross different inbred lines  hybrid exhibits heterosis, better
than either parent
Inbred Parent 1
Inbred Lines
Inbred Parent 1
Inbred Lines
Inbred Parent 2
Inbred Lines
“Single Cross” Corn
• problem was that inbred parents
not very productive, so it is difficult
to produce enough seeds for farmer
Solution = “Double Cross”
Corn
• start with four inbred lines, make 2
single cross hybrids, then cross the
single cross hybrids to produce the
seed corn -= double cross corn
Hybrid Corn
How to cross corn?
• Solution - remove tassels from seed parent
• Solution A = manual labor (college students?) - physically
detassel corn
• Solution B = technological - use male sterile plants
• Problem with solution B - in
1970s, bulk of hybrid corn
utilized one type of male sterile
parent  susceptible to disease
• disease = southern corn
blight - wiped out U.S. crops
early 70s
• solution - back to detasseling;
develop new lines of male
sterile corn
Corn – Natural Diversity
Corn variants
Corn types, Peru farm field
Corn in the U.S.
Sweet Corn
Field Corn: in endosperm sugars  starches
Sweet Corn
Field Corn: in endosperm sugars  starches
Mutant Genes
1. Sugary (su) – slows sugar  starch
Result: more water-soluble
carbohydrates, sweeter, different texture
Standard Sweet Corn
Room Temp. – 50% sugar loss (24 hrs);
5-10 C – 60% (3 days)
Sweet Corn, continued
Field Corn: in endosperm sugars  starches
Mutant Genes
2. Sugar enhancer (se)
Result: higher sugars; sweet, creamy
endosperm
Sugar loss – same as for standard sweet
corn
Germination – about same as for
standard sweet corn
Sweet Corn, Continued
3. Shrunken (sh2) = “supersweet”
Sugar levels 4-8 X higher; higher lipids;
lower starch; different texture (tougher
pericarp)
Storage: room temp., 48 hrs. – 2X sugar
content vs. standard
at 4 C, sugar loss very slow
Poor germination; “Husks are ugly.
Remove for display.”
Sweet Corn, Continued
3. Other genetic modifiers: waxy (wx); brittle (br); brittle2,
amylose extender (ae)  used in combinations with other
genes, will provide new varieties of sweet corn
Important Note: Variants are recessive genes, so they must be
planted in isolation from field corn and sometimes from
other sweet corns
Corn – the C4 crop
Photosynthesis – different pathways
“Normal” = C3
C4 photosynthesis – less photorespiration under warm climates
Forage Grasses
Grasses – important for forage, hay, silage
- uses land that is marginal for other agricultural applications
- in North America, many forage grasses are introduced species
Forage Grasses
Grasses – important for forage, hay, silage
- uses land that is marginal for other agricultural applications
- in North America, many forage grasses are introduced species
Cades Cove, Great Smoky Mountain National Park
- cattle production based on pastures of fescue (Festuca)
- leases expired  periodic burning  encourage native grasses
(bluestem, Indian grass, etc.)  will benefit wildlife
More general application: warm season grasses better adapted to
our climate, with periodic summer drought, can be more
productive than cool season grasses without irrigation
Thursday Lecture – Legumes
Reminder: Exam I Thursday 2/22
Reading: Textbook, Chapter 6