MAIZE(Zea mays L.)

To,Dr Saba TabasumByIMRAN JAFFARMSc (Hons.) 2rd semesterDEPARTMENT OF PLANT BREEDING & GENETICS

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

The Corn Fruit

Evolution of Corn

Corn RelativesTeosinte

Zea diploperennis

Wild Ancestor of Corn:Wild Ancestor of Corn:

Teosinte Teosinte

• Structure of Maize: grass, has terminal staminate inflorescence (=tassels) and lateral pistillate inflorescence (=ear; silks = styles)

Wild Ancestor of Corn:Wild Ancestor of Corn:

Teosinte Teosinte

• Structure of Maize: grass, has terminal staminate inflorescence (=tassels) and lateral pistillate inflorescence (=ear; silks = styles)

Changes from Teosinte to Corn

Teosinte Corn

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

1. Pod corn (husklike glumes)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Types of Corn

1. Pod corn (husklike glumes)

2. Dent corn (soft center)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Types of Corn

1. Pod corn (husklike glumes)

2. Dent corn (soft center)

3. Flint corn (all hard)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Types of Corn

1. Pod corn (husklike glumes)

2. Dent corn (soft center)

3. Flint corn (all hard)

4. Popcorn (core of soft)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Types of Corn

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)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Types of Corn

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)

Differences: mainly related to types of starch (hard vs. soft) in grain.

Breeding of MaizeBreeding 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 MaizeBreeding 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 CornHybrid Corn

• Start with inbreeding initially produce weaker plants “inbreeding depression”

Breeding of MaizeBreeding 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 CornHybrid Corn

• Start with inbreeding initially produce weaker plants “inbreeding depression”

• Cross different inbred lines hybrid exhibits heterosis, better than either parent

Inbred LinesInbred Parent 1

Inbred LinesInbred Parent 1 Inbred Parent 2

Inbred Lines

“Single Cross” Corn“Single Cross” Corn

• problem was that inbred parents not very productive, so it is difficult to produce enough seeds for farmer

• start with four inbred lines, make 2 single cross hybrids, then cross the single cross hybrids to produce the seed corn -= double cross corn

Solution = “Double Cross” Corn

Hybrid Corn

How to cross 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 DiversityCorn types, Peru farm fieldCorn variants

Corn in the U.S.

Sweet CornField Corn: in endosperm sugars starches

Sweet CornField 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, continuedField 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, Continued3. 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