Seed dormancy and hybridization effect of the invasive species, Helianthus annuus

Abstract

Helianthus annuus is an invasive alien species naturalised in the central region of Argentina where it shares an extended area with the sunflower crop. As this species has also invaded several other sunflower crop growing areas in the world, it severely restricts the use of new technologies, for example herbicide tolerance by genetic modification. The natural seed dormancy of the wild Helianthus strains from the centre of origin in North America is well known, but the seed dormancy of the invasive biotypes is still unknown. Dormancy is a fitness trait related to the establishment, dispersion and persistence of invasive weeds. Four experiments were designed to investigate the effect of the pericarp, light, temperature, the after-ripening period and hybridization with the DK3880CL sunflower crop (F1) on the seed dormancy of five invasive H. annuus biotypes. The results showed that pericarp scarification increased imbibition of the whole achene by 19%. Light stimulation only increased germination in the wild biotype without any effect on the domesticated sunflower. A period of 12 months after-ripening at 5°C reduced seed dormancy in the wild biotype and its progeny; the optimal temperature for seed germination at this period was found to be 15°C. Mechanical scarification was the best treatment for overcoming seed dormancy with a differential germination, in the biotypes with the highest response, superior to 63%. Hybridization with domesticated sunflower had a minimal or no effect on seed dormancy but the germination rate was improved in three F1 crosses. Wild biotype dormancy appears to be governed by the maternal pericarp and intrinsic hormone regulation. An increased germination rate of some progenies could constitute an advantage during seedling establishment but only in winters without any frost.

The role of domestication and maternal effects on seed traits of crop–wild sunflower hybrids (Helianthus annuus)

“…For evaluating the maternal effect on seed traits, reciprocal crosses between wild sunflower populations (wild) and cultivated materials (crop) were used. Wild populations were collected in central Argentina (Cantamutto et al ., ): Diamante (DIA; 32°03′S, 60°38′W) and Colonia Baron (BAR; 36°10′S, 63°53′W) which were selected for their contrasting dormancy levels (Presotto et al ., ). Cultivated materials were represented by two commercial cultivars: Cacique CL (CAC; Criadero El Cencerro) and Paraíso 104CL (PAR; Nidera Semillas) which were randomly selected.…”

“…Seeds with PD are water‐impermeable and have a physiological inhibiting mechanism in the embryo that prevents radicle emergence (Baskin & Baskin, ). Embryos excised from PD seeds produce normal seedlings and this kind of dormancy can be broken with gibberellic acid treatments, by scarification, after ripening in dry storage, and with cold or warm stratification (Baskin & Baskin, ; Finch‐Savage & Leubner‐Metzger, ; Presotto et al ., ). In addition, covering structures can prevent germination by restricting the water and oxygen movement, avoid the leaching of inhibitors from the embryo, contain germination inhibitors or physically restrict the emergence of the radicle (Baskin & Baskin, ).…”

“…The F1 crop–wild hybrids usually have intermediate values in most of the traits in which their parents differ (Mercer et al ., ; Presotto et al ., ). Following hybridisation, some early life‐history traits in hybrid populations, like seed traits, strongly depend on the maternal parent (Roach, ; Snow et al ., ; Weiss et al ., ; Alexander et al ., ; Mercer et al ., ; Presotto et al ., ; Pace et al ., ). The maternal parent mainly affects seed traits through the tissues surrounding the developing embryo, especially the pericarp (Roach, ).…”

“…out‐season germination, ability to form soil seed banks and changes in the competitive ability) of the maternal effect on seed traits in crop–wild hybrids. Strong maternal effect on seed dormancy and germination along with slight and variable hybridisation effects have recently been reported in crop–wild sunflower hybrids (Weiss et al ., ; Alexander et al ., ; Presotto et al ., ; Pace et al ., ). However, most of the studies have focused on the crop to wild hybridisation and shallowly explored the morphological and anatomical traits possibly involved in seed germination differences.…”

Disturbance as a factor in breaking dormancy and enhancing invasiveness of African grasses in a Neotropical Savanna

“…Temperature is the main environmental variable involved in the development, control, and the breaking of seed dormancy of species from different ecosystems (Moreira & Pausas 2012;Santana et al 2012;Presotto et al 2014). In our study we simulated the heating effect caused by Cerrado fires on seeds stored in the soil seed bank at 1 cm depth, and that mild temperature of 50ºC (F treatment) affected neither U. decumbens nor U. brizantha germination.…”