Leucaena, Maize Mosaic Virus,
and the Rise and Fall
of the Classic Maya
Civilization
James L. Brewbaker
Dept. Tropical Plant and Soil Science
University of Hawaii
W. Forest Genetics Association
Merida, Yucatan, Mexico July 2000
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The Maya Civilization
 Formative,
Olmec 500 B.C. to 325 A.D.
 Classic
325 to 925 A.D.
Early Classic 325 to 625 A.D.
Florescence 635 to 800 A.D.
Abandonment 800 to 925 A.D.
 Post-Classic, Toltec 975 to 1200 A.D.
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The MAYA
-- A Remarkable Civilization -
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Maya built a culture that survived 6 times as
long as the Roman Empire
Their cities outnumbered those of ancient
Egypt
They flourished while Europe suffered Dark
Ages
Their calendar was the equal of ours, dating
back 0000 years
Their math employed the concept of zero
They predicted eclipses of sun and moon
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MAYA LANDS
 15° - 21° N, 88° - 92° W; 20 million ha
 Atop a Giant Calcareous Plateau
 pH 6.5 - 8.0, High base status (Ca, K)
 Fine soils -- Mollisols, Inceptisols
 Tropical, Mean Annual Temp. 25° - 30°C
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Rainfall; 1000 mm (north), 3000 mm (south)
 South = 2 crops, Central = 1-2 crops; North = 1 crop
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The Classic Maya lacked:
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Metal tools
Beasts of burden (ruminants)
The wheel
Good sources of protein
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Intensive Maize Cropping
Systems of the Classic Maya
Civilization
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Farms created out of high forests without
metal tools
Maize was the primary dietary energy
source
Yucatan Peninsula is calcareous, superb
for year-round production of maize
Much evidence for increasing intensity of
cultivation
Nal-Tel is excellent variety; 1.5 t/ha on
20 kg N, to 5t/ha on 150 kg
Maya ate 2 kg maize/day/family (1t/yr ~
1 ha)
N-fixing Trees and
Maize Cropping Systems
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Mimosoids abundant in Meso-America
Leucaena species are found around most
of the 1300 Maya ceremonial centers
Leafdrop nitrogen avg. 300 kg/ha with
rainfall >1500 mm/yr
N recovered by maize avg. 25% from
leafdrop
Rapid regrowth upon coppicing (e.g.,
canopy closure from randomly spaced
trees in a year)
Alley-farm systems more effective,
“green manure” applied before/during
maize growth
Tikal, Guatemala
Earliest Date = 292 A.D.; Latest = 771
 Population; estimated 200,000
 Major center of Maya (2 million
people)
 60,000 hectares
 Tropical rain forest to 50 m
 Five main pyramids, to 70 m
 Two (+) maize crops per year
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Civilizations; Some Premises
Civilizations Rise and Fall on Their
Stomachs
 Classic Maya Civilization Rose due to
High Maize Productivity
 They Abandoned due to Failure to Sustain
High Maize Productivity
 But it only affected the 2-crop Region
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Collapsed Maize-based Civilizations
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Olmec, Vera Cruz (100 A.D.)
Teotihuacan, Mexico (650 A.D.)
Zapotec, Oaxaca (750 A.D.)
Maya, Yucatan & Guatemala (880 A.D.)
Anasazi, Southwest USA (1050 A.D.)
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Why Abandon Good Maize Land?
 Soil is lost, e.g. erosion on sloping land
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Phosphorus is lost, e.g., harvested off
Nitrogen is lost
Soil irreparably damaged, e.g. salinization
Protracted flooding or drought
Protracted maize diseases or pest damage
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Maize Mosaic Virus (MMV)
Worldwide; Tropical; Lowlands only
 Severe in continuous plantings (e.g. Hawaii)
 Only hosts; Maize, Teosinte
 Only vector; Peregrinus maidis planthopper
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• Thrives only in lowland tropics
• Thrives only on maize and teosinte
• Virus is persistent, transmissible 30 days
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Resistance to MMV
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First described (1910) in Cuban Flint in Hawaii
Shown to be monogenic, Mv locus (1967)
• General resistance, non-racially specific
• Heterozygotes intermediate; Mv BC’d into >100 inbreds
• Mapped with RFLP to 3:80 (1995)
¤ Mv confined to Caribbean races
• Haitian Chandelle (25%), Coastal Tropical Flint (35%), Cuban Flint (20%),
Caribbean (10%), Haitian Yellow (15%), St. Croix (40%), Tuson (35%)
¤ Mv essentially absent from 78 other tested races
• Including all Races conceivably available to Classic Maya
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Early
Hypothesis No. 1
High-yield, sustainable maize production
of the Classic Maya civilization was
enabled by the use of Leucaena species
Leucaena spp. are abundant around Maya
ruins
L. leucocephala, L.
shannonii, L. collinsii
 Maize + Leucaena = excellent
agroforestry
 They have similar environmental
requirements: e.g., Non-acid soils, High
P, High Ca, Good drainage,
Temperature/Moisture
 Leucaena regrowth in a 3-year fallow is
ideal for restoration of maize soil fertility
 Added benefits: food (pods), fuelwood,
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Hypothesis No. 2
Collapse of Classic Maya (9th century)
was precipitated by introduction
of Maize Mosaic Virus
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Classic Maya were limited to one major
genetic source of maize, the variety NalTel
No Mexican or Meso-American varieties
of maize were resistant to MMV
All Caribbean varieties were tolerant to
MMV; the Arawak grew maize in
Haiti/Dom.Rep
Virus-borne leafhoppers easily introduced
from Caribbean islands (e.g., by
hurricanes)
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CONCLUSIONS
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Classic Maya civilization “rose” to great
heights due to excellent yields of yearround maize in mimosoid-rich lowland
tropics
Classic Maya civilization “collapsed” due to
persistent failure of maize crops in 9th
century
Maize mosaic virus is most likely cause of
failure; Nal-Tel highly susceptible
Virus restricted to year-round production
areas in lowlands
Maya retreated to north (Yucatan) and to
south (Guatemala highlands), escaping
virus