1. Thursday Lecture – Corn
Reminder: Exam I - Tuesday 2/22
Reading: Textbook, Chapter 5
Today we will finish our survey of cereal crops, and in particular we will focus our attention on Zea mays, the major cereal crop of the New World region.

2. From Wall Street Journal
Sorghum, whose common name is the same as its scientific one, is native to tropical Africa and was brought into cultivation in Ethiopia. It has been subject to selection for various different uses, including both food and non-food ones, leading to numerous distinctive types.

3. Flour is ground-up ________________ (part of grain)
Quiz
Flour is ground-up ________________ (part of grain)
Name an Old World Cereal crop:
A New World Cereal crop:
Sorghum, whose common name is the same as its scientific one, is native to tropical Africa and was brought into cultivation in Ethiopia. It has been subject to selection for various different uses, including both food and non-food ones, leading to numerous distinctive types.

4. Sorghum Likes it Hot and Dry
Origin: Ethiopia
Sorghum, whose common name is the same as its scientific one, is native to tropical Africa and was brought into cultivation in Ethiopia. It has been subject to selection for various different uses, including both food and non-food ones, leading to numerous distinctive types.

5. Main Types of Sorghum Four main types: grain sorghums
sweet sorghum (animal feed)
Sudan grass (related species)
broomcorn
The grain sorghums are used for human food; the sweet sorghums for animal feed; Sudan grass is a forage crop; and broomcorn is used to make brooms.
See Fig. 5.22, 5.24, p. 125

6. Millets – A Mixed Bag See Table 5.4, p. 126
Millet is a general term used to describe several small cereal grains. Several of these were domesticated in sub-Saharan Africa and are still important food crops in the region. Of these, finger millet and pearl millet are the most significant.
Finger millet – Eleusine coracana
Pearl millet – Pennisetum glaucum

7. Maize – The New World Cereal
Origin: Mexico
Early Spread: Through New World
The crop that we call corn, but more commonly called maize in most of the English-speaking world (the word corn referring to small vegetables such as barley or peas or lentils etc.) is the major cereal crop on which New World agriculture was based and the only one to have attained world-wide importance.

8. Maize – The New World Cereal
Origin: Mexico
Early Spread: Through New World
The crop that we call corn, but more commonly called maize in most of the English-speaking world (the word corn referring to small vegetables such as barley or peas or lentils etc.) is the major cereal crop on which New World agriculture was based and the only one to have attained world-wide importance.
Note on the name:
Corn = small vegetables (barley, peas, lentils)
Maize = from Carib word (spanish mais)

9. The Corn Plant
Corn is a highly distinctive grass. It has the typical grass structure for the plant, although in a very robust mode. The flowers are unisexual, and the grouped in staminate and pistillate inflorescences.
See Fig. 5.26, p. 127

10. Corn Flowers
The staminate inflorescences are terminal, and the structure is not much different than for related grasses. The pistillate inflorescences are lateral, on short branches, and the structure (the “ear”) is highly different from any other grass – the “husks” (modified leaves) enclose pistillate spikelets that are sessile, closely packed together, and produce large grains that are not enclosed by individual bracts (palea or lemma or glumes).

11. Corn Flowers, closer up See Fig. 5.26, p. 127
The familiar “tassel” of the corn plant is the staminate inflorescence – note how the anthers hand out to release the pollen (even though they are wind-pollinated, it is not unusual to see honey bees visiting the staminate flowers to collect pollen – they would not pollinate the plant, however, because they do not visit the pistillate flowers). The “silks” are the styles and stigmas that collect the pollen – note above right how there are silks attached individually to each flower.

12. The Corn Fruit
The fruit of the corn plant, a corn “kernel”, has the typical structure of a cereal grain. There is an embryo (germ) that has a root and shoot end – typically it is in a somewhat depressed area. Corn oil is obtained from this part of the grain. Most of the bulk of the kernel is formed by the endosperm, which is usually rich in starch. The pericarp surrounds the grain, and can be variously colored.

13. Evolution of Corn See Fig. 5.28, p. 130
Corn is so different from any of its relatives that it has provided a puzzle to botanists and anthropologists seeking to understand its origin. Various theories were proposed on how a wild relative might have been modified to produce the corn plant.

14. Corn Relatives Teosinte Zea diploperennis
With increased understanding through use of more sophisticated analytical tools, it is now thought that the wild grass teosinte is not only the direct ancestor to cultivated corn, it is also in the same species, Zea mays. There is one other species in the genus Zea that has been uncovered by field work in remote areas of Mexico – this is perennial corn, Zea diploperrenis. A UT graduate, Dr. Hugh Iltis (now at the University of Wisconsin), was the leader of the expedition that discovered this plant.

15. Wild Ancestor of Corn: Teosinte
Structure of Maize: grass, has terminal staminate inflorescence (=tassels) and lateral pistillate inflorescence (=ear; silks = styles)
Part of the problem in understanding how teosinte could have been transformed into corn is that the positions and structures of the inflorescences are significantly different in the two plants. In teosinte, the inflorescences are bisexual, with pistillate flowers at the base and staminate ones at the apex. Further, the pistillate flowers sit in depressions (“cupules”) that are covered with a hardened glume and arranged in two ranks. In corn, the glumes are soft and do not enclosed the grains, and the pistillate spikelets are arranged in 4-10 ranks.

16. Wild Ancestor of Corn: Teosinte
Structure of Maize: grass, has terminal staminate inflorescence (=tassels) and lateral pistillate inflorescence (=ear; silks = styles)
A comparison of the pistillate inflorescences of maize (above) and teosinte (below) show few obvious similarities. Nevertheless, the conversion between the two structures has been shown to be possible with relatively few gene changes

17. Changes from Teosinte to Corn
See Fig. 5.28, 5.30, p. 130, 132
Teosinte  Corn
Non-shattering pistillate inflorescence (cob)
Corn grains open, glumes soft
Cupule with 2 fertile spikelets, not one
Cupules 4-10 ranked, not 2-ranked
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
Close study has revealed that there are 5 major differences that separate teosinte from corn. Initial studies of interspecific hybrids suggested that the changes are under simple genetic control, so that it is like a switch is flipped from one position to another. More recent studies have shown that the situation is a bit more complicated, but have substantiated the finding that large differences between the two plants were produced by just a few basic changes.

18. Early development of corn
The early development of corn involved selecting for several features, including larger fruits, more numerous pistillate (female) flowers (in part by increasing the number of rows of flowers on the ear), and reduction in the size of the glumes. As with many cultivated plants, there was also selection for various color forms.

19. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

20. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
Dent corn (soft center)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

21. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
Dent corn (soft center)
Flint corn (all hard)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

22. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
Dent corn (soft center)
Flint corn (all hard)
Popcorn (core of soft)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

23. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
Dent corn (soft center)
Flint corn (all hard)
Popcorn (core of soft)
Flour corn (all soft)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

24. Types of Corn
See Fig. 5.29, p. 131
Differences: mainly related to types of starch (hard vs. soft) in grain.
Pod corn (husklike glumes)
Dent corn (soft center)
Flint corn (all hard)
Popcorn (core of soft)
Flour corn (all soft)
Sweet corn (sugars remain)
The numerous cultivars and races of corn can be grouped into a small number of major types, based on the types and distribution of the starch within the corn fruit (kernel). Features of the starch affect the appearance of dent corn (where the characteristic depression in the kernel apex is produced by a pocket of soft starch in the center); popcorn (where the core of soft starch is surrounded by hard starch; heating the kernel causes the soft starch to expand dramatically); and sweet corn, in which the sugars are not polymerized into starch - the kernels tend to shrink when fully mature because of water loss.

25. 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.
In addition to traditional breeding methods based on selection, for corn the use of inbred lines to produce hybrids that exhibit heterosis (“hybrid vigor”) has been a central factor in the agricultural success of this crop in the USA.

26. Breeding of Maize Hybrid Corn
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”
In addition to traditional breeding methods based on selection, for corn the use of inbred lines to produce hybrids that exhibit heterosis (“hybrid vigor”) has been a central factor in the agricultural success of this crop in the USA.

27. Breeding of Maize Hybrid Corn
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”
In addition to traditional breeding methods based on selection, for corn the use of inbred lines to produce hybrids that exhibit heterosis (“hybrid vigor”) has been a central factor in the agricultural success of this crop in the USA.
Cross different inbred lines  hybrid exhibits heterosis, better than either parent

28. Inbred Lines Inbred Parent 1
Forcing corn to inbreed initially produces populations of plants that are less vigorous and smaller than their parental stocks because of inbreeding depression. When different inbred lines are intercrossed, however, the resulting hybrids exhibit a strong heterotic effect (“hybrid vigor”) so that they are even better than the original parents. This image shows two inbred lines (left and right sides of the image) with the hybrid in the center.

29. Inbred Lines Inbred Parent 1 Inbred Parent 2
Forcing corn to inbreed initially produces populations of plants that are less vigorous and smaller than their parental stocks because of inbreeding depression. When different inbred lines are intercrossed, however, the resulting hybrids exhibit a strong heterotic effect (“hybrid vigor”) so that they are even better than the original parents. This image shows two inbred lines (left and right sides of the image) with the hybrid in the center.

30. Inbred Lines
Forcing corn to inbreed initially produces populations of plants that are less vigorous and smaller than their parental stocks because of inbreeding depression. When different inbred lines are intercrossed, however, the resulting hybrids exhibit a strong heterotic effect (“hybrid vigor”) so that they are even better than the original parents. This image shows two inbred lines (left and right sides of the image) with the hybrid in the center.

31. Solution = “Double Cross” Corn
“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
In practice, the yield of seeds from the weak inbred lines was too weak to be economically viable for the seed producers. The solution was to utilize the heterotic effect twice - the first time to produce large amounts of seed corn; the second time the farmer produced the crop. This required starting with 4 inbred lines to produce a double cross hybrid generation.

32. Hybrid Corn
This diagram summarizes the steps required to produce double cross hybrid corn. Although two growing seasons are required, the process can be speeded up by growing at least one set of hybrids in the winter in a warm area such as Florida.

33. Solution - remove tassels from seed parent
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
Because corn is wind-pollinated, it is a challenge to ensure that the seed that is produced represents the hybrid between different inbred lines rather than just selfing within the inbred line. The solution is to remove all of the staminate (pollen-producing) flowers of one of the inbred lines, and to gather the seed from that particular line (which will be outcrossed). Removal of the staminate flowers (tassels) can be done mechanically, but a cheaper method that relied on a phenomenon called cytoplasmic male sterility (cms) came out of research on corn. Breeders were confronted with a problem when they discovered that the major cms line that had been relied on for almost all hybrid corn in the USA was highly susceptible to a new form of the southern corn blight. This emphasized the need for maintaining and increasing genetic diversity among breeding stock.
disease = southern corn blight - wiped out U.S. crops early 70s
solution - back to detasseling; develop new lines of male sterile corn

34. Corn – Natural Diversity
Corn variants
Corn types, Peru farm field
The production of superior agronomic lines of hybrid corns results in a challenge - how to keep the natural diversity of this crop, when farmers who previously produced diverse lines are driven by economic forces to grow the high yielding varieties.

35. Corn in the U.S.
Corn has been a major part of the agricultural success of our country, and is incorporated into an amazing diversity of products, some of which are illustrated on this slide.

36. Sweet Corn Field Corn: in endosperm sugars  starches
Sweet corn is a special type of corn that is eaten fresh, rather than dried, stored, and ground for flour. Its production has relied on mutations to genes that control the conversion of sugars to starches. Recent research into biochemical pathways have produced new mutant types that have superior attributes in producing sweet corns.

37. Sweet Corn Field Corn: in endosperm sugars  starches Mutant Genes
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 is a special type of corn that is eaten fresh, rather than dried, stored, and ground for flour. Its production has relied on mutations to genes that control the conversion of sugars to starches. Recent research into biochemical pathways have produced new mutant types that have superior attributes in producing sweet corns.

38. Sweet Corn, continued Field Corn: in endosperm sugars  starches
Mutant Genes
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
There are several points along the biochemical pathways leading from sugars to starches that can be modified, and the resulting mutant corns have varying properties of sweetness, storage properties, and flavor. The sugar enhancer mutant produces higher amounts of sugars in a sweet and creamy endosperm, although the loss of sugar after harvest is similar to standard sweet corn.

39. Sweet Corn, Continued 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.”
The shrunken gene mutation produces the supersweet cultivars - in these there are not only dramatically higher sugar content, but also the higher lipid and lower starch content results in a different and tougher textgure to the endosperm. The sugar content remains high for a long period after harvest, making this better for shipping and marketing over long distances. The flower, however, is not as good, and the seeds do not germinate as well.

40. Sweet Corn, Continued
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
Continued research has uncovered other potential points of modification, and in the future new varieties of sweet corn will be developed which may have better growth or taste characteristics. Almost all of the variants are the result of the effects of recessive genes, which means that these varieties of sweet corn must be planted in isolation from other corns so that transfer of dominant genes through cross pollination does not remove the desirable traits.

41. Corn – the C4 crop Photosynthesis – different pathways “Normal” = C3
C4 photosynthesis – less photorespiration under warm climates
Corn is a plant that exhibits a type of photosynthesis that is favorable for warm climates compared to the “standard” type in most other grasses. Future research and understanding of the biochemistry and genetics of this type of photosynthesis holds the promise of transferring it to other crops such as wheat or rice, where it could boost yields.

42. 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
In addition to the uses of grasses to produce grains forfoods, grasses are also significant sources of food for herbivores, which can derive their nutrition from the vegetative parts of the plants (stems and leaves). Forage grasses are important agriculturally and in particular can represent the best use of land that is marginal for other applications.

43. 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
In addition to the uses of grasses to produce grains forfoods, grasses are also significant sources of food for herbivores, which can derive their nutrition from the vegetative parts of the plants (stems and leaves). Forage grasses are important agriculturally and in particular can represent the best use of land that is marginal for other applications.

44. Thursday Lecture – Legumes
Reminder: Exam I - Thursday 2/22
Reading: Textbook, Chapter 6
On Tuesday we will have our first exam. We will continue our coverage of economically important plants on Tuehursday when we consider the uses and importance of legume crops - read Chapter 6 before then.