A large scale study by University of Queensland researchers has opened the door for targeted breeding programs that could help find a genetic solution to the problem of drought-induced sorghum lodging.
Their findings are the culmination of decades of study, with the focus now set to turn to breeding sorghum with greater resistance to lodging.
Professor David Jordan from UQ's Queensland Alliance for Agriculture and Food Innovation said lodging occurs when a crop with high yield potential is subjected to water stress when it is producing grain.
"Losing a bumper grain crop just before harvest because plants fall over is heartbreaking for growers and undermines profitability and global efforts to improve food security," Prof Jordan said.
Working with the Department of Agriculture and Fisheries at the Hermitage Research Facility in Warwick, Prof Jordan found that lodging occurs whenever water scarcity stopped photosynthesis.
"This forces the plants to rely on carbohydrates stored in the stems," he said.
"The metabolic shift ultimately weakens the stems, culminating in their death, while pathogens can invade and further weaken stems, causing them to break."
But in a catch-22 situation, the research team has found traits used to drive up yields, such as plant height, introduced a susceptibility to lodging.
"Obviously the seed companies are trying to pick hybrids with the highest yield that they can but at the same time if a hybrid lodges severely it will be killed off commercially, even if it only falls over in a small minority of places, this reduces the efficiency of breeding programs as resources are wasted on hybrids that fail," Prof Jordan said.
"The biggest impact of lodging has been not so much the losses in the field as the loss of access to high yielding hybrids that would be useful in a range of situations.
"The big advance in this study was to find a way to look at genes that improve standability and don't affect grain yield, otherwise we're stuck with this see-saw situation where we select for one trait and one goes up but the other one goes down."
He said to meet this challenge, scientists undertook one of the world's largest genome-wide association studies in sorghum.
"This study looked at 2308 unique hybrids grown in 17 Australian sorghum trials over three years," he said.
"A genome-wide view of the genetics is important as it means we can search the network of lodging-associated genes for those pathways we can target for improvement without sacrificing yield potential."
Central Queensland grower Paul Murphy, whose farm is located 40km north east of Emerald, said lodging was a problem that varied from season to season.
"Some years it's under five per cent of your crop, other years it might be 20pc," he said.
"It's a real balancing act... you could almost cure lodging but the way to cure lodging also drives your yield right down. What we need to do is get adequate yield with minimum lodging."
Mr Murphy said the work of Prof Jordan and his team was incredibly important to the industry.
"They're not going to have a silver bullet but the knowledge they share is absolutely critical in managing the problem," he said.
Prof Jordan's team found one way to increase stem strength would be to alter the composition of the molecules used by the plant to assemble the supportive cell wall, while bolstering disease resistance at the same time would offer additional protection.
The research team is now working to share their insights with seed companies and translate their findings into targeted breeding strategies.
Previously, Queensland sorghum researchers introduced greater drought resistance into Australian hybrids by transferring 'stay-green genes' from sorghum sourced from Ethiopia but Prof Jordan said the industry had reached a stage where it needed to look elsewhere for answers.
"With new technology we can do things a lot faster than we used to," he said.
"We use gene markers to rapidly select for genes because otherwise the only way we could select for genes was to look at trials in the field and see which hybrids fall over and which ones don't.
"Now we can use these markers to test for specific genes that give us improved lodging resistance and don't influence yield, which will allow us to really speed up the breeding process."
The sorghum core pre-breeding project was funded by the Department of Agriculture and Fisheries Queensland, Grains Research and Development Corporation and UQ.