Grain breeding’s ‘Holy Grail’, a drought tolerant, high yielding crop, could be achievable if researchers understand, design and act upon crop plant improvement programs for drought conditions, according to plant stress expert, Abraham Blum of the Volcani Centre, Tel Aviv, Israel.

Addressing the Grains Research and Development Corporation supported ‘Adaptation of Plants to Water-Limited Mediterranean-type Environments’ international symposium at CSIRO Perth, last week, Dr Blum said the association between drought resistance, water use efficiency (WUE) and yield potential was often misunderstood.

“This can lead to conceptual oversight and wrong decisions in implementing breeding programs for drought-prone environments. Most breeding programs target high yield potential, which might not be compatible with superior drought resistance.

“On the other hand, high yield potential should therefore be reviewed in the context of its effect on and interaction with drought resistance and WUE on the background of the prevalent drought profile in the target environment,” Dr Blum said.

According to Dr Blum, drought resistance is a function of dehydration avoidance, rather than desiccation tolerance.

“Plant production in water limited environments is often affected by constitutive plant traits that allow maintenance of water plant status, rather than by stress adaptive responses that support plant function at low water status.

“A major adaptive response sustaining crop production under drought stress is osmotic adjustment. Despite past speculation, there is no proof that osmotic adjustment entails a cost in terms of reduced yield potential.”

WUE for yield is often equated with drought resistance, which is not necessarily so, according to Dr Blum.

“Apparent genotypic variations in WUE are normally expressed by variable water use.

“Reduced water use, which is reflected in higher WUE, is generally achieved by plant traits and environmental responses that reduce yield potential.

“Under most dryland situations, where crops depend on unpredictable seasonal rainfall, the maximisation of soil moisture use is a crucial component of drought resistance, or avoidance, which is then often expressed in lower WUE.

“The effect of a single drought adaptive gene on crop performance in water-limited environments can be assessed only when the whole system is considered in terms of drought resistance, WUE and yield potential,” Dr Blum said.

Most of the information on drought resistance breeding is available on Dr Blum’s website, www.plantstress.com