Lecture 15: Evolution of crop plants and the Green Revolution

Question 1

domestication of edible plants has allowed man to

Answer 1

produce food in larger quantities (and to move from hunter-gatherer)

Question 2

domestication of edible plants: over the last 10,000 years this has occurred especially in areas..

Answer 2

irrigated (supply water) from rivers, such as the yellow river, the Nile, the Tigris, and the Indus

Question 3

Large scale food production enables (and is enabled by):

Answer 3

• community settlement (towns, cities) and accompanying population increase
• the cultural & political evolution that accompanies these

Question 4

how plants change with domestication:

Answer 4

• loss of dispersal mechanisms (Maize, wheat, bean)
• loss of dormancy (wheats, oats, rice)
• conversion from perennial to annual (rice, rye, cassava)
• loss of fruit production (yam, sweet potato)
• loss of seed production (banana, citrus)
• Increase in size of: –seed (legumes,cereals)
• -fruit (squash)
• -storage organ (cassava, carrot)
• loss of bitterness
• -cucurbits (cucumber, melon, squash)

Question 5

plants, such as _____, are completely dependant on man for dispersal

Answer 5

corn & wheat

Question 6

maize’s ancestor =

Answer 6

TEOSINTE ( a lot smaller with less corn)

Question 7

morphological variation in maize cobs; old to new

Answer 7

• grown in size and girth, lots more corn

- use to be wrapped in ‘husk’

Question 8

the mutation to unlock corn kernels:

Answer 8

• corn use to be locked in husk

- single amino acid substitution (Lys -> Asp) in tga1 key to the development of ‘naked’ kernels

Question 9

ploidy =

Answer 9

number of sets of chromosomes in a cell

Question 10

evolution of wheat: looking at ploidy

Answer 10

• started as 2 diploids (AA, BB)
• these crossed producing 3 tetraploid species (AABB)
• crossing with another diploid (DD) produced one hexaploid form (AABBDD)

Question 11

Evolution of wheat: During evolution towards a cultivated form:

Answer 11

• plants developed a tougher rachis (stem/axis of the ear). A brittle rachis aids seed dispersal
• free threshing grain (not hulled)
• increased duration of grain filling
• increased grain size
• delayed senescence of upper leaves (LAI & LAD higher)
• larger leaves & decreased photosynthesis on leaf area basis
• reduced tillering
• in Aegilops spp, the small slow-growing ears may be largely self-supporting for photosynthate

Question 12

hull/husk =

Answer 12

toughened plumes surrounding grain

Question 13

how is grain dispersed in primitive wheats?

Answer 13

dispersed with the brittle rachis and/or flower parts (hull/husk also present)

Question 14

rice domestication involved a ________ which reduced shattering:

Answer 14

a single gene mutation
-selection of a single nucleotide mutation in a transcription factor (sh4) necessary for the normal development of ann abscission layer that separates grain from the pedicel

Question 15

evolution of grain dispersal in barley:

Answer 15

• wild barley spikes are brittle at maturity due to think cell walls at rachis nodes
• this characteristic evolved by duplication & neofunctionalisation of two genes, Btr1 & Btr2
• during domestication, deletion sin Btr1 or Btr2 converted the rachis to non-brittle
• the deletions happen twice: the first in the South lLvant (btr1) and then in the North Levant (btr2)

Question 16

increase in crop yields: world wheat and rice grain yields increased massively in

Answer 16

• the 1960’s and 70’s = the ‘Green Revolution’
• the growth of crop yields was such that agriculture was now able to outstrip (overtake) population growth
• per capita production increased every year following

Question 17

introduction of shorter-strafed varieties of cereals:

Answer 17

need for shorter, more logging-resistant, wheat after growers began planting winter wheat early and applied large amounts of N fertilisers
-new wheat varieties were shorter, had increased harvest index and were more resistant to damage by wind & rain

Question 18

the green revolution: the harvest index definition

Answer 18

• proportion of total production present in grains, tubers etc
• harvest yield= economic yield/biological yield X 100

Question 19

Norman Borlaug’s work in Mexico:

Answer 19

• Norman Borlaug developed new strains of crops which yielded 4X as much food = saved lives
• Borlaug obtained early crosses and lines from Vogel in 1953
• he crossed them with Mexican varieties giving increase yield not only due to non-lodging, but greater number of stems, grains per ear and better grain filling
• Non-photoperiod sensitives so could grow two crops per year
• Pictic 62 and Penjama 62 released in 1961
• By 1963, 95% of Mexico’s wheat crops used these semi-dwarf varieties

Question 20

Breeding of short-strawed varieties of cereals:

Answer 20

• result of Green revolution
• Short strawed varieties respond abnormally to the growth hormone, gibberellin (stimulates stem elongation, germination & flowering), known to be equivalent to the Arabidopsis Gibberellin Insensitive (gai) gene

Question 21

short-strawed varieties:

-gai mutants in Arabidopsis show:

Answer 21

• reduced plant height

- increased amounts of gibberrellic acid

Question 22

transgenic rice expressing the gai gene:

Answer 22

• Basmati rice (N and NW India) has long, translucent white grain, cooks well and has a pleasant aroma.
• Tall plants, with weak stems, susceptible to damage by wind and rain, causing yield losses and reduction in grain quality.
• Conventional breeding methods to dwarf Basmati 370 led to loss of its unique characteristics.
• Transgenic plants carrying the gai gene were 30% dwarfed with respect to control, without loss of desirable characteristics.