Abstract
In Australia, turnip weed has been rapidly emerging as one of the major weeds in conservation agricultural systems. Germination and emergence of turnip weed were examined for two populations collected from Gatton and St George regions of Australia; two locations with high and low rainfall, respectively. The seeds of turnip weed germinated at all the tested temperatures, but germination was the lowest at 15/5°C, intermediate at 20/10°C and highest at 25/15°C and 30/20°C. The results indicated a high adaptability of turnip weed to warm environmental conditions, although it is a major problem in the winter season. Germination was higher in dark than light/dark regimes except at 30/20°C. Three was a concomitant reduction in germination as the osmotic potential values decreased from 0 to -1.0 MPa. There was 2 and 4% germination at -0.8 MPa for Gatton and St George populations, respectively, and no germination occurred at an osmotic potential of -1.0 MPa. There was a reduction in germination when the sodium chloride (NaCl) concentration was increased from 0 to 150 mM, and no germination was observed at 200 and 250 mM of NaCl. Turnip weed germinated over a broad range of pH (4 to 10). Seedling emergence was higher at 1 cm depth compared to 0.5 cm or at the soil surface. There was 28 and 33% emergence at the surface for the Gatton and St George populations, respectively, compared to 48 and 56% emergence from 1 cm depth for the Gatton and St George populations, respectively and no emergence was observed from 6 cm depth. The results indicated that tillage leading to shallow burial would promote the emergence of turnip weed; on the contrary, tillage that could bury seeds deep into the soil profile might minimise the emergence. Under ideal conditions and lack of integrated weed management programmes, this weed will emerge, set seeds and enrich the soil seed bank and thereby continue to be a problem in the northern grain region of Australia.
Highlights
Weeds of Brassicaceae are rapidly emerging under conservation agricultural systems in Australia as these weeds could adapt to varying environmental conditions and prevailing crop management practices [1,4, 7]
This difference between populations from South Australia and Queensland in their germination response to dark could be ascribed to the difference in weather, difference in cropping systems [5], and changes that have been occurring in the agronomic management over time
Potential of turnip weed to germinate under varying temperature and light regimes point to the adaptability of this weed to infest the cropping regions and fallows of the northern regions of Australia
Summary
Turnip weed (Rapistrum rugosum (L.) All.) is a major agricultural weed from the family of Brassicaceae that is rapidly increasing in prevalence in Australia, Iran, USA and Russia [1,2,3,4]. Weeds of Brassicaceae are rapidly emerging under conservation agricultural systems in Australia as these weeds could adapt to varying environmental conditions and prevailing crop management practices [1,4, 7]. Germination of Brassicaceae weeds and in particular turnip weed is not limited by dark conditions [6, 9, 10]. The presence of seed coat ensures a physical barrier leading to periodicity in germination and will expose to different environments that are highly conducive for emergence, growth, and reproduction [9]
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