Germination and seed persistence of Amaranthus retroflexus and Amaranthus viridis: Two emerging weeds in Australian cotton and other summer crops

Abstract

Redroot pigweed (Amaranthus retroflexus L.) and slender amaranth (Amaranthus viridis L.) are becoming problematic weeds in summer crops, including cotton in Australia. A series of laboratory and field experiments were performed to examine the germination ecology, and seed persistence of two populations of A. retroflexus and A. viridis collected from the Goondiwindi and Gatton regions of Australia. Both populations of A. retroflexus and A. viridis behaved similarly to different environmental conditions. Initial dormancy was observed in fresh seeds of both species; however, germination reached maximum after an after-ripening period of two months at room temperature. Light was not a mandatory prerequisite for germination of both species as they could germinate under complete darkness. Although both species showed very low germination at the alternating day/night temperature of 15/5 C, these species germinated more than 40% between ranges of 25/15 C to 35/25 C. Maximum germination of A. retroflexus (93%) and A. viridis (86%) was observed at 35/25 C and 30/20, respectively. Germination of A. retroflexus and A. viridis was completely inhibited at osmotic potentials of -1.0 and -0.6 MPa, respectively. No germination was observed in both species at the sodium chloride concentration of 200 mM. A. retroflexus seedling emergence (87%) was maximum from the seeds buried at 1 cm while the maximum germination of A. viridis (72%) was observed at the soil surface. No seedling emergence was observed from a burial depth of 8 cm for both species. In both species, seed persistence increased with increasing burial depth. At 24 months after seed placement, seed depletion ranged from 75% (10 cm depth) to 94% (soil surface) for A. retroflexus, and ranged from 79% to 94% for A. viridis, respectively. Information gained from this study will contribute to an integrated control programs for A. retroflexus and A. viridis.

Effects of Four-Week Exposure to Salt Treatments on Germination and Growth of Two Amaranthus Species

“…Amaranths were also reported as tolerant to low and moderate salinity during germination, although there is a large variability, sometimes even among genotypes within the same species. The seed germination of the noxious weed A. retroflexus from China was higher upon 150 mM NaCl treatment than under control conditions [52], whereas for seeds collected from Queensland (Australia), the germination percentage dropped by 50% at only 100 mM NaCl conditions [53]. Moreover, large varia-tions in germination percentages under salt were reported in cultivars of edible A. cruentus from Benin [26].…”

Biomass Production of an Overwinter Cover Crop with Biofumigation Properties in New Mexico

“…Seeds that did not collapse under gentle pressure were considered viable and are hereafter referred to as persistent. Responses to gentle pressure have been used for assessments of weed seed viability (Borza et al 2007;Khan et al 2022), including assessments of seed viability for Palmer amaranth (Korres et al 2018). To our knowledge, previous reports for pressure assessments of seed viability did not include information on the amounts of force applied to individual seeds.…”

Environmental influences on common waterhemp germination and tolerance to salinity and herbicides

“…However, reports of similar studies on other Amaranthus species are available. For example, Khan et al (2022) reported that F I G U R E 3 Germination percentage (mean ± standard error of mean) of Amaranthus tuberculatus seeds under the effect of pH levels. The bars with the same lowercase letters are not significantly different according to the Fisher's Least Significant Difference test at a 0.05 level of significance.…”