Inferences of Cassava’s
domestication
relating to progenitor(s), location, and
time. With additional information
regarding its current uses worldwide,
capacities of various systematic
techniques, and use of ancient starch
grains as a taxonomic tool.
Andrew Gifford Gardner
Adopted from Conclusions made primarily by Kenneth Olsen and
Barbara Schaal, but also from Dolores Piperno and Luiz Carvalho
Cassava (Manihot esculenta Crantz ssp. esculenta
tapioca, manioc, mandioca, yuca
A primary calorie source for over 500 million people,
the major source of carbohydrates in sub-Saharan Africa,
and the sixth most important crop worldwide
-butIt affords almost no cash value,
has low vitamin and protein values,
and is susceptible to pathogens, especially in Africa.
Largely ignored by breeding programs and scientists
despite its importance.
Systematics of Manihot
a genus of 98 neotropical species, with
habits ranging from
herbs to small trees, and extreme
morphological plasticity.
Morphology-based taxonomic systems
have proven to be problematic, especially
in elucidating the relationship between
cassava and the rest of the genus.
Resulted in a “compilospecies”
hypothesis
Olsen and Schaal’s generic systematics
a traditional molecular phylogenetic approach, sampling species which had been
previously implicated as potential progenitors of cassava.
ITS maximum
parsimony tree
Two major findings:
South American and Mesoamerican species for two distinct clades.
Cassava is clearly a member of the South American clade, with nearly
identical sequences to M. esculenta ssp. Flabellifolia.
Three main
domestication
questions:
1. Is cassava derived from M.
esculenta ssp. Flabellifolia?
2. Is M. esculenta ssp.
Flabellifolia a feral escape from
cultivated cassava?
3. Is cassava only partly derived
from M. esculenta ssp.
Flabellifolia? In other words,
is there evidence of
hybridization?
Three main domestication questions:
Olsen and Schaal used population genetics
to answer these questions:
1. Is cassava derived from M. e. Flabellifolia?
Supported if cassava’s genetic diversity were a
subset of M. e. Flabellifolia’s.
Three main domestication questions:
Olsen and Schaal used population genetics
to answer these questions:
2. Is M. e. Flabellifolia a feral escape from
cultivated cassava?
Supported if M. e. Flabellifolia’s genetic
diversity were a subset of cassava’s.
Three main domestication questions:
Olsen and Schaal used population genetics to
answer these questions:
3. Is cassava only partly derived from M. e. Flabellifolia? In other
words, is there evidence of hybridization?
Supported if cassava’s genetic diversity were a
subset of M. e. Flabellifolia’s, but also contained
genetic material not present in M. e. Flabellifolia.
They used low-copy nuclear genes and
microsatellites for their analyses.
Taxa included were the “core of the core”
cassava germplasm collection (20 landraces),
157 M. e. Flabellifolia individuals
representing much of the range (within Brazil),
and 35 M. pruinosa individuals where the species is
sympatric.
Results
Haplotype gene tree (G3pdh)
□ M. e. Flabellifolia
◊ cassava
○ M. pruinosa
The other two genes
corroborate the patterns
seen in this tree.
Results
Maximum likelihood tree of
microsatellite allele frequencies
P - M. Pruinosa
The vertical bar
represents the
cluster of wild
populations most
closely related to
cassava
Results
Partially shaded G3pdh haplotype shared
with cassava
Fully shaded At least 2 of 3 nuclear genes
share haplotypes with
cassava
Vertical bars Populations grouped with
cassava in the microsatellite
analysis
Three main domestication questions:
1. Is cassava derived from M. esculenta ssp. Flabellifolia?
YES.
2. Is M. esculenta ssp. Flabellifolia a feral escape from
cultivated cassava?
NO.
3. Is cassava only partly derived from
M. esculenta ssp. Flabellifolia? In other words,
is there evidence of hybridization?
NO. (but it may occur between M. pruinosa and M. esculenta ssp. Flabellifolia)
Starch grains through history
(or, the work of Dolores Piperno)
Elucidation of cassava’s history of
domestication
has been challenging.
Root crops preserve extremely poorly
in the humid tropics, and the earliest
undisputed macrobotanical remnants
of cassava are from 4,000 BP on the
arid coast of Peru.
Starch grains through history
(or, the work of Dolores Piperno)
fortunately, domesticated cassava starch grains differ
greatly from other species, including M. e. Flabellifolia
common bean
cassava
sweet potato
Starch grains through history
(or, the work of Dolores Piperno)
She is working at Aguadulce rock shelter in Panama.
Cassava starch on an edge-ground cobble,
which should date to nearly 7,000 BP.