Dispersal of Avena fatua and Avena sterilis patches by natural dissemination, soil tillage and combine harvesters

Abstract

The dispersal of Avena spp. (A. fatua and A. sterilis) by natural dissemination and by agricultural operations was studied in four experiments conducted in Spain and Britain. Natural dispersal was very limited, with a maximum dispersal distance of 1.5 m. Dispersal was higher in the geographic direction that was downwind than in any of the other three geographic directions. Although plant movement was very small under notillage, an annual patch displacement of 2-3 m in the tillage direction was observed under conventional soil tillage. Ploughing downhill resulted in much larger dispersal distances than ploughing uphill. In the crops studied, combine harvesters dispersed few Avena spp. seeds, because of the fact that the plants had shed most of their seeds (>90%) before harvest. The percentage of seeds available to be dispersed by the combine was dependent on the harvest time. Although combine harvesting may not contribute much to short-distance dispersal, it may play an important role in long-distance dispersal. In our studies, isolated plants were located up to 30 m from the original sources. This small proportion may have a significant effect on the distribution of the weed within a field, acting as foci for new patches.

Genetic diversity of six arable plants in relation to their Red List status

“…Seed dispersal rates and distances decrease because of restricted animal movement (Fahrig 2007) and for arable plant species more so because of modern seed cleaning procedures. Seed dispersal via farming machinery is another possible option, but most seeds are dispersed over only very short distances in this way (Marshall and Brain 1999;Barroso et al 2006).…”

“…Agricultural machines may transport diaspores around dispersal barriers and over larger distances (Barroso et al 2006), but pairwise genetic distances confirm that all populations differed [see Mantel test, Table 8 in Appendix (online)]. Population sizes were estimated by counting the individuals of several smaller patches and projecting the size to the whole patch.…”

Potential for seed-mediated gene flow in agroecosystems from transgenic safflower (Carthamus tinctorius L.) intended for plant molecular farming

“…Crop seed is a propagable material as well as a major commodity, and may be distributed locally and internationally (Saji et al 2005) with consequence to international trade. Volunteer populations of transgenic canola (oilseed rape, Brassica napus L.) have been found, initiated by seed spill during transport (Saji et al 2005;Yoshimura et al 2006) and weed and crop seed dispersal by farm machinery in and among fields is well documented (Blanco-Moreno et al 2004;Shirtliffe and Entz 2005;Barroso et al 2006). Seeds may germinate, producing volunteer plants and the seeds from these populations serve as secondary sources of gene flow (Yoshimura et al 2006).…”

Effects of relative emergence time and water deficit on the timing of fruit dispersal in Raphanus raphanistrum L.

“…Seed banks allow weeds to persist through cropping phases and extend weed infestations (Fenner 1995). During the normal harvest of grain crops, retained weed seeds enter the harvester, are separated from the grain, and distributed over the field by the chaff-spreading system of the harvester (Barroso et al 2006;Blanco-Moreno et al 2004;Rew et al 1996;Shirtliffe and Entz 2005;Walsh and Powles 2007). Mechanisms targeting escaped weed seeds in the chaff fraction, such as HWSC systems, have been developed to either remove seeds via chaff carts or destroy seeds through seed destructors at crop harvest (Shirliffe and Entz 2005;Walsh et al 2012;Walsh and Newman 2007;Walsh and Powles 2007).…”