Hope for heat-tolerant sorghum

Image of a trial site

Field experiment validation at the University of Queensland/CSIRO research station at Gatton, Queensland.

PHOTOS: Vijaya Singh 

Researchers have discovered new genetic diversity in sorghum that could help growers in the northern grains region sustain yields in the face of more extreme temperatures.

Researchers from the Queensland Alliance for Agriculture and Food Innovation (QAAFI), including the University of Queensland and CSIRO, have identified heat-tolerant sorghum lines that commercial breeders can use to develop new hybrids in the next five to 10 years.

“Our key message to growers is that we’ve found genetic variation for heat-tolerance around flowering,” said Dr Scott Chapman, a senior researcher from CSIRO, speaking at a recent GRDC Grains Research Update.

“We now know the trait characteristics that enable a sorghum plant to withstand extreme temperatures, and we have a screening procedure that allows us to identify better germplasm.

“With follow-on research it’s possible to develop improved sorghum parent lines that can be fed into the commercial hybrid production system,” he said.

High-heat days increasing

Many sorghum growers in northern cropping regions are concerned about the increasing frequency of high-heat days. Over the past 40 years, weather records have shown that days with temperatures higher than 36°C have increased from about seven to more than 30 a year.

Image of two heads of sorghum

The effect of different temperatures on a susceptible sorghum genotype in a controlled environment at CSIRO’s St Lucia research facility at the University of Queensland: (left) a high-temperature treatment (38°C maximum) and (right) a control treatment (32°C maximum).

Dr Chapman says temperatures higher than 38°C damage the viability of a plant’s pollen, which leads to decreased seed production and reduced yield.

“In a sustained heat event, up to 95 per cent of the grain can be damaged in some plant lines,” he said.

With GRDC support, CSIRO and QAAFI researchers explored the potential to develop ‘climate-ready’ sorghum and wheat varieties adapted to increased temperatures.

Professor Graeme Hammer’s team at QAAFI discovered naturally high genetic diversity in sorghum, with some parent germplasm showing tolerance to high-heat temperatures of over 38°C.

The research showed that certain sorghum varieties are more sensitive to heat than others, and plant lines found to be completely susceptible to daily maximum temperatures of 38°C retained only five per cent of their grain, while others retained 60 to 70 per cent grain.

“The implications of this heat tolerance are that growers should be able to improve yield and reduce risk through the selection of suitable sorghum hybrids,” Professor Hammer says.

Planting times

“Currently, whenever sorghum growers get sufficient rain to plant, they have to make decisions about which hybrid they’re going to sow and when,” Professor Hammer says. “Such a decision influences the timing of plant flowering and whether it will coincide with extreme temperatures.”

Using an existing farming systems model, modified for heat effects on sorghum, the team has shown that the most risky sowing time in warmer locations is from early to mid-October. Avoiding this planting time is an immediate management measure that might help reduce yield losses due to extreme heat events.

“Planting in early to mid-October increases the risk that high temperatures – experienced throughout late December and early January – could coincide with the emergence and flowering of the seed head,” Professor Hammer says.

“This is a time when the crop is most susceptible. In the medium to long-term, heat-tolerant hybrids are needed as the ‘risky heat window’ will become wider with increasing temperatures.”

The research has provided Australia’s sorghum breeders with access to methods and lines that are expected to enable the transfer of heat tolerance into existing commercial hybrids.

“The main research needs are to improve the selection methods, survey the germplasm resources more widely and identify genetic markers to speed up the development of tolerant lines.”

More information:

Professor Graeme Hammer, QAAFI,
07 3346 9463,
g.hammer@uq.edu.au;

Dr Scott Chapman, CSIRO,
07 3214 2254,
scott.chapman@csiro.au

Video of Scott Chapman discussing heat tolerance in sorghum

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