New research could help sorghum growers predict disease risk
Author: Toni Somes | Date: 06 Nov 2017
Growers planning to plant sorghum this summer have had their battle against costly charcoal rot and fusarium stalk rot boosted by research into how disease causing pathogens survive in soil and stubble between crops.
Stalk rot causes yield loss through poor grain fill, but more commonly through plant lodging which impedes harvest and reduces grain quality.
With investment from the Grains Research and Development Corporation (GRDC), researchers have focused on the two most important pathogens causing stalk rot, Macrophomina phaseolina, (causing charcoal rot) and Fusarium species (causing fusarium stalk rot) to be better able to predict the disease risk of a paddock.
In a recent GRDC disease update, Associate Professor Adam Sparks from the University of Southern Queensland’s Centre for Crop Health said stubble seems to be a substantial contributor to pathogen populations for charcoal rot.
“In the 2016/17 summer season, thirty-two sorghum fields were sampled from across the south-east and central Queensland and northern New South Wales regions and the samples analysed using the molecular PREDICTA B test, to identify Macrophomina, and to determine the severity of this pathogen that causes charcoal rot,” Associate Professor Sparks said.
“At the end of the growing season, all sites were re-visited and on-ground disease assessments of sorghum crops were conducted at each sample location.
“Early results from soil and stubble sample analysis confirmed the endemic nature of the pathogen, with Macrophomina being detected at every site sampled. Only seven per cent of samples had low population densities, while 66 per cent of samples had high Macrophomina population densities.
“We are examining different sampling methods for the existing PREDICTA B test with the aim of eventually determining if levels found in soil and stubble can be correlated with end of season disease levels found in a mature crop. If so, this will provide growers with a risk assessment for potential disease likelihood prior to planting.
“These preliminary results do demonstrate that despite the soil borne nature of Macrophomina, stubble contributes substantially to the pathogen population,” he said.
Similarly, for fusarium stalk rot, pathogens survive on sorghum residue once the crop has been harvested but researchers would like to know how long it can survive under various conditions.
A field trial was established at the Queensland Department of Agriculture and Fisheries’ Hermitage Research Facility in 2014 to determine the length of survival of F. thapsinum on colonised sorghum residue and identify the implications of different stubble management practices.
Using standing, surface and buried stubble treatments, samples were taken over the next two years to examine F. thapsinum levels.
Study results show that at 12 months, the rate of recovery of F. thapsinum inoculum from infected stubble was lower in buried (33.8%) and surface treatments (42.5%), compared with standing stubble (74.5%). However, by 18 months, differences between treatments appear to have reduced, with F. thapsinum recovered the least from buried stubble (31.5%), followed by surface stubble (35.5%) and then standing stubble (40%).
“These preliminary results suggest that under the weather conditions which occurred during the trial approximately one third of the initial F. thapsinum inoculum remained in the stubble after two years irrespective of the management of the stubble,” Associate Professor Sparks said.
“The development of a molecular PREDICTA B test for F. thapsinum and F. andiyazi is underway, which may provide an indication of future disease risk, although the role the weather plays in these outbreaks is significant and cannot be ignored or understated,” he said.
Further detail on current management strategies for charcoal rot and fusarium stalk rot can be found via this link.
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