Environmental factors affecting the germination and seedling emergence of two populations of an emerging agricultural weed: wild lettuce (Lactuca serriola)

Abstract

Wild lettuce (Lactuca serriola L.) is a significant emerging agricultural and environmental weed in many countries. This invasive species is now naturalised in Australia and is claimed to cause significant losses within the agricultural industry. Sustainable management of wild lettuce has been hampered by a lack of detailed knowledge of its seed ecology. Laboratory-based studies were performed to examine the potential influence of environmental factors including temperature and light conditions, salinity, pH, moisture availability and burial depth on the germination and emergence of two spatially distant populations of wild lettuce. Results suggested that the germination of wild lettuce seeds occurred across a broad range of temperature conditions (12-h cycle: 30°C/20°C, 25°C/15°C and 17°C/7°C) for both populations. We also found that these seeds are non-photoblastic; germination was not affected by darkness, with >80% germination in darkness for both populations at all tested temperature ranges. Germination significantly declined as salinity and osmotic stress increased for both populations, with seeds from the Tempy population were more affected by NaCl >100 mM than seeds from Werribee, but in neither population was there any observed effect of pH on germination (>80% germination in both populations at all tested pH ranges). For both populations, germination significantly decreased as burial depth increased; however, the two populations differed with regard to response to burial depth treatment, whereby seeds from the Tempy population had higher emergence than those from Werribee at 0.5 cm burial depth. These results suggest that light-reducing management techniques such as mulching or use of crop residues will be unsuccessful for preventing germination of wild lettuce. By contrast, burial of seeds at a depth of at least 4 cm will significantly reduce their emergence.

Can rotations improve management of herbicide-resistant annual sowthistle (Sonchus oleraceus) and prickly lettuce (Lactuca serriola) in lentil production systems of southern Australia?

“…Seedbank recruitment is unlikely to be the major contributor since both species have little dormancy and most seed will germinate within the first year provided the necessary cues. Chauhan et al (2006) reported >90% germination in annual sowthistle, and Chadha et al (2019) reported >85% germination in prickly lettuce following exposure of seed to light and moisture, with germination and emergence declining with increasing osmotic potential and depth of seed burial. However, the lack of substantial rainfall events in 2018 and seed burial at seeding could have resulted in some persistence of viable seed produced in 2017 to the 2019 season.…”

“…These rainfall events occurred several weeks before the 2019 Presow assessment at RS2 and the 2019 Pretreat assessment at both sites. Germination in both weed species is highly moisture dependent and large rainfall events stimulate flushes of germination (Chadha et al 2019;…”

“…These species are often found growing in association with each other and readily colonize open habitats such as roadsides, cropland, and other disturbed areas (Hutchinson et al 1984;Weaver and Downs 2003). They have become more common in annual cropping systems in Australia since the widespread adoption of reduced tillage systems because the seeds remain close to the soil surface (Weaver and Downs 2003;Widderick et al 1999), which favors germination of both species (Chadha et al 2019;Chauhan et al 2006). These weed species can affect yield in subsequent crops by depleting soil moisture in summer fallows (Widderick et al 2010), and a recent study has demonstrated yield loss in wheat due to competition at high densities of annual sowthistle (Manalil et al 2020).…”

“…Therefore, the weed seedbank within a field can increase considerably following a season in which a weakly competitive pulse crop has been grown. However, seedbank persistence in both species is short under field conditions, with little or no innate dormancy (Chadha et al 2019;Chauhan et al 2006). Provided cues of light and moisture, germination rates of greater than 80% have been reported in both species, whereas factors such as seed burial or drought conditions can increase the proportion of seed that persists in the seed bank beyond a season (Chadha et al 2019;Chauhan et al 2006).…”

Germination biology of three populations of Navua sedge (Cyperus aromaticus)

“…The germination biology of various populations of weed species is known to vary under different environmental conditions (Chadha et al 2019;Loura et al 2020). Within the infestation region in Queensland, Australia, variable environmental conditions occur for rainfall and temperatures, and therefore weed populations may differ in their responses to these different environments and may require different management practices (Cai et al 2005;Iqbal et al 2019;Whitfield and Queensland Department of Environment and Resource Management 2010).…”