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.

Adopted from Conclusions made primarily by Kenneth Olsen and Barbara Schaal, but also from Dolores Piperno and Luiz Carvalho

Andrew Gifford Gardner

Cassava (Manihot esculenta Crantz ssp. esculentatapioca, 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

-but-

It 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 systematicsa traditional molecular phylogenetic approach, sampling species which had been

previously implicated as potential progenitors of cassava.

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.

ITS maximum parsimony tree

Three maindomestication

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 remnantsof 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

cassavacommon bean

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.