Caption: Soil microbiologist Dr Kirsty Owen,
Department of Agriculture, Fisheries
and Forestry (DAFF).
Nematode populations following the summer crop rotation hold important implications for wheat variety selection and yield performance.
- Root-lesion nematodes are present in approximately 70 percent of fields in the northern grain belt and can slash yields by up to 50% in wheat and 20% in chickpeas.
- All major winter crops, wheat, barley and chickpeas, are susceptible to the root-lesion nematode species Pratylenchus thornei and encourage the proliferation of nematode populations.
- Growers are urged to conduct soil testing for nematodes, particularly if a susceptible crop was grown in the 2013/14 summer season.
Growing a tolerant wheat variety in paddocks harbouring high populations of root-lesion nematodes is critical if growers are to avoid devastating yield losses of up to 50 percent.
Recent trials supported by the Grains Research and Development Corporation (GRDC) and conducted by the Department of Agriculture, Fisheries and Forestry (DAFF) found that management of nematode populations through the summer crop rotation held important implications for the performance of following wheat crop.
In presenting the trial data at the recent GRDC Northern Research Update at Goondiwindi, DAFF soil microbiologist Dr Kirsty Owen said it was critical that tolerant rather than intolerant wheat varieties were grown when the root-lesion nematode species Pratylenchus thornei (P. thornei) was present at damaging levels.
“If intolerant wheat varieties are grown, growers risk a yield reduction of up to 50 percent,” Dr Owen said.
“The research found that growing one resistant crop, such as sorghum, maize or sunflower did not provide a quick fix in a field that started with damaging levels of 2500 P. thornei/kg soil.
“Populations of P. thornei did not fall below damaging levels and the next intolerant wheat lost 44%–51% in yield compared to a tolerant wheat variety.”
While P. thornei did not die out completely even after five successive resistant crops, Dr Owen said a significant reduction in nematode populations was possible by growing several resistant crops.
However she urged growers to conduct soil testing for nematodes, particularly if a susceptible crop such as mungbean or soybean was grown, as monitoring was essential to the on-going management of crop and variety selection.
The summer crop rotation trials consisted of two trials planted in adjacent fields in December 2011. The first field had low P. thornei populations (<125/kg soil) with a cropping history of five resistant crops since 2004 - cotton, maize and sorghum while the second field had moderate P. thornei populations (2500/kg soil) and a cropping history of wheat, sorghum, wheat.
Several cultivars of mungbean, soybean, sunflower, maize and sorghum were planted in each field in a replicated design with sufficient plots to plant wheat varieties EGA Wylie (tolerant) and Strzelecki (intolerant) in 2013. An unplanted bare fallow treatment was also included in the trial.
After harvest of the summer crops nematode populations were recorded to 120 cm soil depth.
At the moderate P. thornei site, nematodes were found to 90 cm soil depth and populations were greatest at 0–15 cm soil depth.
Populations of P. thornei after growing sorghum, sunflower and maize were similar to bare fallow (range of 2,900–4,500/kg soil at 0–15 cm) and there were no significant differences between varieties within each of these crop species.
In contrast, populations of P. thornei increased after growing mungbean or soybean compared to sunflower, sorghum, maize or clean fallow and there were significant differences between the soybean and mungbean varieties.
At the low P. thornei site, nematodes were detected to 60 cm soil depth and below that depth populations were extremely low or zero.
There were no significant differences in P. thornei populations among the different summer crops and varieties and while overall, populations increased five times compared to pre-summer plant populations, they remained low at below 250/kg soil.
Importantly, Dr Owen said there were no differences in biomass or grain yield of the summer crops between the low and moderate P. thornei sites and as the summer crops grown were tolerant to P. thornei, no yield loss was suffered.
In terms of the impact on the following wheat crop, the site that started with moderate P. thornei populations saw a yield reduction on the intolerant wheat variety Strzelecki of 49% compared to the tolerant wheat variety EGA Wylie (1.9 tonnes/ha after Strzelecki compared to 3.7t/ha after EGA Wylie).
In contrast, at the site that started with low P. thornei populations there was only a 4% difference in yield between Strzelecki and EGA Wylie (3.6t/ha and 3.7t/ha respectively). The yield of cv. Strzelecki increased 47%, or 1.7t/ha, at the low P. thornei site compared to the moderate P. thornei site.
“Yield of Strzelecki was lowest following soybean (1.6t/ha) and greatest following maize and sunflower (2.1t/ha),” Dr Owen said.
“An unexpected result was that there were no significant differences in yield of Strzelecki after fallow, sorghum and mungbean.
“This result may be partly due to dry conditions during the 2011-12 summer and following winter season which limited nematode multiplication, particularly after the susceptible mungbean crop.
“Additionally and importantly, the results support the theory that one resistant crop in sequence was not enough to sufficiently reduce populations of P. thornei.”
Nevertheless, Dr Owen said the trial results had found a strong negative relationship between populations of P. thornei after the summer crops and yield of the following intolerant wheat Strzelecki.
In contrast, there was no relationship between populations of P. thornei and yield of the tolerant wheat EGA Wylie which Dr Owen said was expected due to the good P. thornei tolerance of EGA Wylie.
At the low P. thornei site, there was no relationship between yields of the tolerant and intolerant wheat and populations of P. thornei after growing the summer crops. Populations were below the damage threshold for wheat Strzelecki.
Louise Morgan, DAFF Senior Media & Communication Officer
07 3087 8576
Sarah Jeffrey, Senior Consultant Cox Inall Communications
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