Longevity of Horseweed Seed Bank Depending on the Burial Depth

Abstract

-Horseweed (Conyza spp.) is considered as one of the major weeds occurring in the agricultural areas of South America, especially in Brazil. This species stands out from the other weeds due to characteristics such as large seed production, continued seed production, dispersion over long distances and resistance to 5-enolpyruvoylshikimate 3-phosphate (EPSP) and acetolactate synthase (ALS) inhibiting herbicides, features that increase their management. Therefore, this study aimed at determining the physiological quality and longevity of horseweed seeds over 12 months. The experiment was established under field conditions, using a randomized block design with four replications. Fifty horseweed seeds were distributed into 50 g of dry soil, placed in permeable nylon mesh bags (10 x 10 cm), which were buried at 1, 2, 4 and 8 cm of depth. Each month, for 12 months, samples were collected and washed with water, and the remaining seeds were submitted to germination test. The percentage (%) of remaining seeds, germination, abnormal seedlings, dead seeds, dormancy and viability were evaluated. It was found that the horseweed seed bank was reduced by 59 % over 12 months. Moreover, horseweed seeds develop a secondary dormancy, regardless of the burial depth. In addition, an increased burial depth increases longevity and physiological seed quality.Keywords: Conyza spp., survival, dormancy, germination, viability. RESUMO -

Burial depths favor Italian ryegrass persistence in the soil seed bank

“…Similar results were reported for seed viability in Conyza bonariensis (L.) Cronq. with losses up to 59 % for periods shorter than 360 DAB (Vargas et al, 2018). At 180 DAB, burial depth of 0.5 cm exhibited approximately 45 % of deteriorated seeds compared to 5-20 cm burial depths with values 35 and 28 %, respectively.…”

“…Similarly, the maintenance of seeds near the surface layer favored dormancy breakage and increased the percentage of non-viable dormant seeds compared to seeds buried deeper than 5 cm (Figure 5B). In agricultural systems, germination and biological processes, such as deterioration and predation of weed seeds, are stimulated by the presence of seeds on the soil surface, providing better conditions for management of soil seed bank (Goggin et al, 2012;Scherner et al, 2016;Vargas et al, 2018). Other characteristics associated the soil seed bank dynamic involve complex interactions with each kind of weed species (dormancy), environmental conditions (light, temperature, and soil moisture), biological processes, such as predation and allelopathy, and soil management practices (harrowing and/or plowing) that can affect persistence of soil seed banks (Graeber et al, 2012;Scherner et al, 2016).…”

“…Low viability of weed seeds was also reported in Amaranthus palmeri S. Watson (Korres et al, 2018), Conyza bonariensis (L.) Cronq. (Vargas et al, 2018) and Lolium rigidum Gaudin. (Narwal et al, 2008), which presented short persistence, depending on the burial depths.…”

Cover plants as a suppression and increasing tool to hairy fleabane control

“…Another important factor is the low weight of the seed and the reduced reserves amount, favoring the physical and allelopathic effects of the mulch on the survival of seedlings and seeds. These characteristics were observed in an experiment with C. bonariensis seeds in the soil seed bank managed under no-tillage system, with a 6% monthly viability reduction for seeds allocated up to 2 cm due to greater microbial activity and predation (Vargas et al, 2018).…”

Stressful Conditions Affect Seed Quality in Glyphosate Resistant Conyza bonariensis (L.)

“…Great efforts have been made to characterize the factors involved in the glyphosate resistance, dispersal, and management of C. bonariensis, including growth analysis and bioecological aspects [10]. In considering its seed biology, there is abundant information regarding Conyza's seed germination growing degree days requirements for different sowing dates (autumn, winter, and spring) and agricultural environments [10], as well as its seed viability [11,15], emergence times over a growing season [16], seed longevity [17], and some aspects related to seed quality, such as factors related to seed production, dead seeds, empty seeds, and dormant seeds, among others parameters [18,19]. However, studies on how stress conditions (cold or heat) affect the seed quality of glyphosate-resistant C. bonariensis-which may contribute to its management by reducing seed persistence, reducing the soil seed bank, and consequently preventing the emergence of weeds at critical times [20]-are scarce.…”