Breeding goals of yield increases, root quality improvement, and disease re
sistance in cassava are considerably slowed down by biological characterist
ics of the crop, which includes a long growth cycle, a heterozygous genetic
background and a poor knowledge of the organization of crop diversity. The
se factors severely hamper the speed and ease of moving around useful genes
in cassava. The consequences are that cassava production fails to keep up
with demand, especially in regions where over 90% of yield is consumed as f
ood, leading to an increase in acreage of cassava fields mostly into margin
al lands. The advent of molecular markers, genome studies and plant genetic
transformation holds promise of providing ways around breeding obstacles i
n long growth cycle and heterozygous crops. A number of these new tools, in
cluding a molecular genetic map, markers linked to disease resistance genes
, and marker-aided studies of complex traits now exist or are being develop
ed for cassava at CIAT. Large scale sequencing and mapping of expressed seq
uence tags (ESTs) have been initiated, towards a transcript map of cassava
and the implementation of the candidate-gene approach to complex trait mapp
ing. A cassava bacterial artificial chromosome (BAC) library has also been
constructed to expedite positional cloning of genes, known only by their ph
enotypes and their position relative to markers on a molecular genetic map
and complementation studies of candidate loci. Studies of genes that contro
l traits of agronomic importance, and their allelic diversity in nature, pr
ovides powerful tools for understanding the basis of crop performance and i
mprovement.