Wheat varieties with improved heat stress tolerance during stem elongation to the end of grain fill is an area of research that could regularly boost yield by 10 to 30 percent.
These features to a degree are appearing in some new releases, simply because these varieties have performed better than older varieties in variety trials that are conducted in typical trying seasonal conditions.
However research dedicated to finding traits with superior heat stress tolerance, combined with high yield in non-stressful situations, aims to accelerate development of more hardy durable varieties.
Wheat (Triticum aestivum) is a complex genetic plant with enormous potential for finding new traits like improved heat tolerance. It is a plant based on two natural separate hybridisation events with three grass species (T. Urartu, T. speltoides and Aegilops tauchii) thousands of years ago.
Following each hybridisation, the chromosome numbers doubled spontaneously resulting in fertile wheat.
Synthetic wheat, derived from crosses between ancestors of bread wheat with current durum wheat varieties provide a great source of unexplored genetic variability and improved traits like high yield, heat tolerance and water use efficiency having at least 30 percent higher yielding potential than existing wheat cultivars.
Rebecca Thistlethwaite and Professor Richard Trethowan, Sydney University, with research based at the Narrabri Wheat Research Foundation are leading a GRDC funded study seeking improved heat tolerance in wheat.
High temperatures at anthesis cause pollen sterility and affect the number of viable florets. High grain filling temperatures influence both kernel number and kernel weight. Both these heat stress periods commonly occur and mechanisms of tolerance to both stresses are critical in germplasm development.
Their research approach is to use a three-tiered phenotyping process where they identify heat tolerant material in the field at multiple locations and multiple times of sowing (Narrabri, VIC and WA).
Selected promising lines from field trials are then assessed more comprehensively in field-based heat chambers. Superior lines are then more intensely heat treated under glasshouse conditions.
Ms Thistlethwaite reports their research has identified line with considerable improved heat tolerance to current varieties. Research such as this is linked with other programs across the world. Breeding material is accessed from various international programs also seeking attributes like improved heat tolerance.
