TTeecchhnniiccaall
IInnnnoovvaattiioonn BBrriieeff
No. 7, November 2010
CGIAR Systemwide Program
on Integrated Pest
Management (SP-IPM) is a
global partnership that draws
together the diverse IPM
research, knowledge, and
expertise of the international
agricultural research centers
and their partners to build
synergies in research outcomes
and impacts, and to respond
more effectively to the needs
of farmers in developing
countries.
SP-IPM Technical Innovation
Briefs present, in short, IPM
research findings and
innovations for the
management of pests, diseases,
and weeds in agricultural
production.
This and other IPM Briefs are
available from
www.spipm.cgiar.org
Sowing the seeds of better yam D. Coyne, A. Claudius-Cole, H. Kikuno
Pests and diseases of seed tubers compromise yam production
Numerous pests and diseases affect yam tubers. Nematodes, a particular concern, manifest during storage and
facilitate tuber rot by fungi and bacteria. Viruses, on the other hand, can be devastating in the field during the
growing period. Most bio-constraints affect seed productivity and viability, reducing germination, plant vigor and
yield. The use of good quality and healthy seed material is
therefore a crucial foundation for high and sustainable yam
production, as it is for other clonally propagated crops, such as
potato. The use of diseased seed tubers results in the
production of small, poor quality ware yam and a persistent
cyclical decline. To prevent the introduction of pests and
diseases into the production cycle, it is essential that healthy
planting material is supplied to producers. However, obtaining
healthy seed yam is one of the biggest problems for growers.
Some farmers use their own seed stock, harvested from the
previous season, while others obtain the seed material from
specialized seed yam producers.
Sub-surface necrosis caused by lesion nematodes.
– D. Coyne
Producing healthy seed yam
As with potato, yam seed material should be generated following strict production and phytosanitary guidelines
to ensure high quality and disease-free seed stock. Dedicated seed producers are best suited for the supply of
seed material. Farmers who prefer to generate seeds for their own use should set aside areas specifically for
seed production. Seed yam should be produced by planting setts cut from a larger tuber which will provide whole
seed yam of a suitable size as planting material; a relatively high level of care has to be applied because cut
surfaces increase the likelihood of tuber rot and desiccation. Minisetts of 25 g have proved successful (Kalu et
al., 1989). However, farmers in West Africa prefer larger sized setts. These are less likely to fail and require less
attention, especially under more marginal or risky conditions. An optimum size for the setts with which farmers
felt comfortable and which produced favorably sized seed was 75-100 g spaced 25 cm on rows and with up to 1
m between rows. Rows spaced closer together can be used, but may require nutrient and irrigation supply.
Uncut whole seed tubers are best suited for the production of ware yam, rather than cut pieces from a larger
tuber. Whole seed material reduces seed loss, particularly under marginal or stressed conditions. The supply of
healthy, suitably sized whole seed tubers for use as planting material should therefore be a priority aim.
To generate healthy stocks, it is important to use the best possible quality yam for planting. The seed stock then
acts as the superior quality material for the successive generation of seeds. This ‘rolling stock’ should then be
regularly examined and treated as necessary to maintain high quality. A strict system for the identification,
removal, and destruction of plants infected with viruses in the field needs to be rigorously employed.
For healthy seed stocks, three treatments can be employed to produce (or maintain) planting material free of
pests and with very low presence of pathogens:
Hot water treatment
Exposure to a temperature of 50-55°C for 20-25 minutes
disinfests tubers of most pests and pathogens. A large
container that can be heated, into which yam tubers are
submerged, preferably with a thermostat that will help
maintain the water at a constant temperature, is required.
The container can be constructed locally.
Gas fuelled hot water tank with yam ready for dipping.
– P. Spiejer