Yams

Question 1

What are Yams plants?

Answer 1

Genus Dioscorea, 644 species, family: Dioscoreaceae

dioecious twining climbers, occasionally both male and female flowers can be found on same plant

all species of economic importance are tuberous

main tropical food yam species are D.alata, D.rotundata … p. 3

produce a tuber as an annual underground storage organ, which shrivels away when regrowth commences, and a new tuber can be formed simultaneously

Yams has been neglected by research, 13’000 references for 644 species whereas maize has 1 species and 300’000 references

Question 2

Domestication and distribution of tropical yams

Answer 2

D. alata was domesticated after arrival of the Australoids, 60’000 years ago in the present New Guinea or Melanesia

D.esculenta is an ancient crop in the Pacific. THe species wa most likely introduced onto Fiji / Melanesia / New Guinea between 3500 and 3000 BP

D. rotundata started to be domesticated in West Africa 7000 yr ago

Question 3

Yam yield in Africa and Asia

Answer 3

High tuber yields reported for Eastern Asia and Melanesia

Tuber yields remain low (around 10 t/ha) in Africa

Surfaces under yam increased in West Africa from 0.8 M ha in 1961 to 7 M ha in 2016

High yields can be obtained on limited surfaces

Question 4

Yams in Europe

Answer 4

France, Germany and Switzerland have Yams production

Question 5

Why do you grow yams?

Answer 5

For food:
Staple food, famine food, “healthy” food, processed food: puree, frites, fufu, boiled, cake, bread

For cash:
In Côte d’Ivoire, depending ont he tome ant the yam species / variety, you will get between less than 100 CFA/kg tuber to more than 500 CFA/kg

For medicinal / dermatological use:
Dioscorea spp. can contain allantoin and steroidal saponins, Products currently derived from wild yam species

For culture:
new yam festival in west Africa and Melanesia
Stories regarding Yam

Question 6

How do you grow Yam? (West Africa)

Answer 6

Almost no external input
Yam cropping possible only 2 yrs after each other
On farm yields <10t fresh tuber/ha
(potential yield around 50t/ha)

trees are burned and the Yam is planted in ashes

Question 7

Challanges in yam production

Answer 7

Low yielding varieties
“seed” quantity: 1/3 of harvest is traditionally used as “seed” for new plantation
“seed” sanitary quality: nematodes, viruses, fungi, mealybugs
Pests and diseases on foliage
weeds
Staking/needs for wood
Soil fertility decline
Losses during tuber conservation
too much work
markets are not transparent
no agricultural extension
no high added value products
not interesting for policy makers
negative impact on biodiversity/forest

Question 8

YAMSYS case study

Answer 8

p. 15 - 21

Question 9

Innvations developed in the YAMSYS project

Answer 9

Increase planting density of yam from 1 plant on several m2 to 1 plant/m2
- reduces cropped surface
- reduces labor
- allow for water harvesting

Healthy “seeds”
- improves crop establishment
- better quality of harvested tubers
- less storage losses

Use improved germplasm and crop rotation
- use of legumes (for nitrogen fixation)
- decrease the pressure of pests and diseases
- reduce the rate of deforestation for yam cultivation

Improved staking
- requires less wood, hence decrease in deforestation
- reduces weed pressure
- maintains soil moisture
- exposes foliage better to sunlight hence increased yields

Balanced fertilizer application (mineral and organic)
- improve plant growth
- improve tuber quality
- increase yields

Improve seed storage
- maintain seed quality until the next planting season
- reduce storage losses
- improve crop establishment and productivity

Question 10

Impact of fertilization and rotation on tuber yield of D. alata

Answer 10

High yield variability, but very good yields
Large differences between sites
generally higher yields in year 3 than year 1

Question 11

See slides for more information on the YAMSYS

Answer 11

slides