Hot weather in January is virtually a given in northern Australia but the question on producers’ lips is “how hot”?
Sorghum growers looking to plant in November are being urged to weigh up the risk of excessively high temperatures occurring in January and coinciding with critical development phases of crops.
Recent research backed by the Federal and Queensland Governments and the Grains Research and Development Corporation (GRDC) has highlighted the implications of heat stress for pollen viability, even in crops that are not moisture stressed.
The research found the most severe impacts on yield occurred when high temperatures around flowering reduced the viability of sorghum pollen causing reduced seed set and yield loss, according to Professor Graeme Hammer, Director of the University of Queensland’s Centre for Plant Science at the Queensland Alliance for Agriculture and Food Innovation (QAAFI).
“In recent controlled environment experiments, where plants were exposed to high maximum temperature conditions for five day periods, high temperatures coinciding with flowering gave the greatest reduction in seed set. The sorghum was sensitive for a period of 10-12 days over flowering,” Prof. Hammer said.
“The research work has given us a much better understanding of the interaction between variety and temperature.
“We have incorporated this effect into the APSIM sorghum crop model and are conducting simulations for sites and sowing dates across the sorghum growing region using the last 50 years of climate data to examine yield and temperature stress risks.
“While individual years vary significantly in sowing date effects on grain yield, there is not a large effect of sowing date on average sorghum yield and yield likelihood across all years.”
The modelling suggests that in northern NSW and southern Queensland, average yield isn’t impacted until sowings in mid-January however the modelling doesn’t take into account other issues such as disease and harvesting problems which can be encountered with late sowing.
“Seed set in sorghum is reduced by high temperature effects on pollen and that effect is most prevalent for October and November sowings which flower during the peak risk time of year,” Prof. Hammer said.
Simulations for Gunnedah that assessed the relative effects of high temperature on yield simulated on a year-by-year basis with an annual sowing date of October 15, found that there were very few years when the most tolerant genotype was affected, but the least tolerant genotype was affected often.
“This demonstrates the potential for introducing tolerance into elite sorghum hybrids by breeding. We are continuing our pre-breeding research to identify physiological mechanisms and genomic regions/genes responsible for conferring this tolerance,” Prof. Hammer said.
“We are also looking at consequences on these risks of trends in climate that indicate heatwave conditions are likely to increase in frequency.”
Caption: Professor Graeme Hammer, Director of the University of Queensland’s Centre for Plant Science at the Queensland Alliance for Agriculture and Food Innovation (QAAFI) says research suggests that seed set in sorghum is reduced by high temperature effects on pollen and that effect is most prevalent for October and November sowings, which flower during the peak risk time of year. Photo supplied by QAAFI.
Professor Graeme Hammer, UQ Centre for Plant Science
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Sarah Jeffrey, Senior Consultant Cox Inall Communications
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