Biology, Ecology, Distribution and Control of the Invasive Weed, Lactuca serriola L. (Wild Lettuce): A Global Review

Lactuca serriola L. (wild lettuce) is a highly invasive C3 weed in many countries, including Australia, Canada, and the USA. This weed is a severe threat to agricultural systems, especially in crops grown with reduced or no-tillage approaches, which commonly include wheat, cereals and pulses. Owing to the vertical orientation of its leaves in the north-south plane and its root architecture, L. serriola can maintain high water use efficiency under drought conditions, giving it the ability to expand its range under a drying climate. Each plant can produce up to 100,000 seeds which have no primary dormancy and form a short-term seedbank lasting up to three years. Most seedlings emerge in autumn and overwinter as a rosette, with a small flush of emergence in spring depicting staggered germination. Research into control methods for this weed has been performed, and these methods include chemical herbicides applied alone and in combination, the establishment of plant competition, tillage, mowing and bioherbicide. Herbicides can provide effective control when applied in the seedling or rosette stage; however, spring germination is difficult to control, as it skips the rosette stage. Some biotypes are now resistant to ALS inhibitor and synthetic auxins, causing concern regarding using herbicides. A dedicated integrated management plan for 3–4 years is recommended for the control of this troublesome species. This review will explore the biology, ecology, distribution, current control techniques and previous research on this weed, allowing us to make recommendations for its future research and management.

Nutritional, antioxidant, angiotensin-converting-enzyme and carbohydrate-hydrolyzing-enzyme inhibitory activities of underutilized leafy vegetable: African wild lettuce (Lactuca taraxacifolia Willd)

Background African wild lettuce (Lactuca taraxacifolia Willd.) is an underutilised indigenous leafy vegetable containing essential nutrients and medicinal properties. Hence, this study aimed to determine the chemical composition, antioxidant activities, α-amylase, α-glucosidase and angiotensin converting enzyme inhibitory potentials of wild lettuce leaves powder samples. Methods Freshly harvested Wild Lettuce leaves were processed into whole leafy powder (WLF), extracted powder (WLE), residue (WLR) and leaf protein isolate (WPI). Chemical composition, antioxidant activities, α-amylase, α-glucosidase and angiotensin-converting enzyme inhibitory potentials of the powder samples were determined. Results Crude protein of Wild Lettuce leaves ranged from 23.27 to 46.57 and crude fiber from 4.17–37.37 g/100 g. Phosphorous was the most abundant element, while zinc had the lowest concentration. The samples essential amino acids, protein efficiency ratio, essential amino acid index and biological values were 39.83–50.65 mg/100 g protein. 2.79–3.51, 77.03–92.36% and 72.26–88.97%, respectively. Saponin, tannin, oxalate, phytate, terpennoids, flavonoid and phenol in the leafy vegetable samples were within tolerable levels. The African wild lettuce leaf protein isolate (WPI) had higher DPPH antioxidant activity (91.88%), percentage inhibitory properties on α-amylase (26.11%), α-glucosidase (64.24%) and angiotensin-1-converting enzyme (97.53%) than WLF (18.28, 25.44, 55.41 and 67.56), WLE (70.85, 24.97, 62.53 and 93.27) and WLR (53.07, 24.68, 50.03 and 85.28) respectively. Conclusion African wild lettuce leaf samples, particularly protein isolate, contain essential nutrients, antioxidant activities and ability to inhibit angiotensin-1-converting, α-amylase and α-glucosidase enzymes Therefore, the leafy vegetable samples, particularly WPI, may be suitable as antioxidant, antidiabetic and antihypertensive agent.

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

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.