On the horizon drought-tolerant wheats

FARMERS in semi-arid areas could realise dramatic yield increases - from 1.5 tonnes per hectare to 3 or 3.5 tonnes - with new varieties being developed at the International Maize and Wheat Improvement Centre (CIMMYT).

"CIMMYT's work brings higher wheat yields to . farmers throughout the world, including those in difficult environments like Australia," said Sanjaya Rajaram*, director of the Centre's Wheat Program. "In CIMMYT's wheat germplasm we have evidence that yield potential is far from exhausted. Recent hybrids produced at CIMMYT, for example, could ultimately increase yields by 10-I 5 per cent above those of currently planted commercial varieties."

By blending traditional drought-tolerant wheats, improved high-yield-potential wheats and synthetics from CIMMYT, his program had bred experimental wheats in the Yacqui Valley of Mexico. These yielded well on a single irrigation of 120 mm for the entire growing season (noting that as much as 50 mm of additional moisture may be present in the soil or atmosphere).

CIMMYT breeders are working on other drought-resistant traits including earlymaturing varieties that could escape moisture stress at the end of the cycle, as well as latematuring wheats that slowed their development to benefit from late rains.

Dr Rajaram said new wheats under development had produced up to 30 per cent more grain than their parents under tough dry land conditions. Drought-tolerance genes inherited from the wild ancestor goat grass had made the difference. Seedlings of the new wheats were so vigorous they could force their way up through crop residues and from lower soil depths.

This vitality came from roots that anchor them firmly in the ground and from long, strong coleoptiles that pushed through the soil and any stubble on the surface. Plants also protected themselves from drought by producing numerous leaves that extended outward horizontally and quickly covered the ground, shading the soil and conserving moisture.

Built-in nutrients Dr Rajaram said another exciting area was research on grainthat was bred to be naturally rich in micronutrients such as iron and zinc.

"As it is the most widely consumed crop in the world, improving wheat's nutrient content could have a significant impact on human nutrition. CIMMYT is addressing this challenge in collaboration with the University of Adelaide," he said.

But future world demand cannot be met unless yields grow by an additional 60 kg per hectare per year, and world hunger cannot be reduced without greater support for international agricultural research.

Dr Rajaram said it was unlikely that the anticipated productivity growth in high potential environments would meet the growth in demand to 2020, and improved productivity in marginal areas could be a key means of attaining food security in the coming years.

In the last two decades, in fact, wheat yield potential had risen at a more rapid rate in marginal areas than in favourable environments - about 3.1 per cent per year, compared with I per cent in irrigated areas.