The advent of saturated molecular maps promised
rapid progress towards the improvement of crops
for genetically complex traits like drought resistance
via analysis of quantitative trait loci (QTL). Progress
with the identification of QTLs for drought resistancerelated
traits in rice is summarized here with the
emphasis on a mapping population of a cross
between drought-resistant varieties Azucena and
Bala. Data which have used root morphological traits
and indicators of drought avoidance in field-grown
plants are reviewed, highlighting problems and
uncertainties with the QTL approach. The contribution
of root-growth QTLs to drought avoidance
appears small in the experiments so far conducted,
and the limitations of screening methodologies and
the involvement of shoot-related mechanisms of
drought resistance are studied. When compared to
Azucena, Bala has been observed to have highly
sensitive stomata, does not roll its leaves readily, has
a greater ability to adjust osmotically, slows growth
more rapidly when droughted and has a lower wateruse
efficiency. It is also a semi-dwarf variety and
hence has a different canopy structure. There is a
need to clarify the contribution of the shoot to
drought resistance from the level of the biochemistry
of photosynthesis through stomatal behaviour and
leaf anatomy to canopy architecture. Recent
advances in studying the physical and biochemical
processes related to water use and drought stress
offer the opportunity to advance a more holistic
understanding of drought resistance. These include
the potential use of infrared thermal imaging to study
energy balance, integrated and online stable isotope
analysis to dissect processes involved in carbon
dioxide fixation and water evaporation, and leaf
fluorescence to monitor photosynthesis and photochemical
quenching. Justification and a strategy
for this integrated approach is described, which has
relevance to the study of drought resistance in
most crops.