Wheats types differ in drought response
By Edward Long
WHEAT varieties are showing clear differences in their ability to withstand drought.
That is the conclusion of a three-year HGCA-funded research project undertaken by the University of Nottinghams Department of Agriculture at Sutton Bonington and NIAB.
Estimates suggest 20% of the UK wheat crop is grown on drought-prone soils. Failure to use varieties which can tolerate lack of rain could cut yields and profits.
"There are a number of desirable traits which combine to give a variety the ability to cope with drought stress," says Sutton Boningtons John Foulkes. "The main one is an ability to amass and store soluble carbohydrate in the stem up to and shortly after flowering. This can later be remobilised to buffer the effects of late drought on grain yield. Another factor could be improved rooting, which provides a better chance for a plant to find soil moisture."
Dr Foulkes says there are two critical stages in a crops development which determine its susceptibility to lack of moisture. The most obvious is between post-flowering and grain-fill. The other is earlier, around growth stage 31 when tiller survival is determined.
"Of all the varieties we have tested Rialto seems best able to cope with drought conditions at both critical periods," Dr Foulkes says. "The amount of soluble stem carbohydrate in the varieties ranges from 1.5 to 3.5t/ha. Rialto has the highest level of all. With Haven it consistently amasses about 1t/ha more than Spark or Hereward. Brigadier is not far behind, while Riband is near the bottom with Spark."
Haven, on ADAS Gleadthorpes sand in Nottinghamshire, yielded 9.82t/ha (3.97t/acre) after late drought, slightly more than Rialtos 9.54t/ha (3.86t/acre). Both outstripped the 8.71t/ha from Riband.
Earlier maturing varieties develop rapidly, and may have shallower rooting systems than later types. So they take longer to grow through the critical period between GS 31 and 39 than those with deeper roots.
Varieties which get off to a good start and reach GS 31 before others, have an advantage if drought sets in early. Rapid initial development helps crops avoid potential trouble. Rialto reaches GS 31 about 3-4 days before Hereward and 9-10 days before Haven or Spark.
The Nottingham researchers believe one possible explanation for Sparks consistently poor performance is its late development. It does not start flowering until summer days are long, so fails to pack in sufficient stem reserves to tide it over.
Cheltenham-based AICC member Jonathan Oliver of Gloucester Independent Agronomy says the HGCA research will help.
"A lot of my clients grow wheat on drought-prone Cotswold land. Hussar seems more reliable than Brigadier. But at Velcourts Open Day, I was particularly impressed with Rialto. I am recommending that my customers try it." *
• Varieties differ.
• GS31 critical for tillers.
• Post-flowering to grain fill affects yield.
• Rooting and early season storage of assimilates buffers drought.
• Rialto and Haven best, 1t/ha better than spark or Hereward.
• Information in 1997 Cereals Variety Handbook.