Abstract
Abstract: Paspalum dilatatum Poir. is a promising perennial summer grass forage for temperate regions, but among other factors, slow stand establishment has hindered its adoption. One of the reasons may be seed dormancy. Intraspecific variability in seed dormancy has been reported in P. dilatatum, but the mechanisms underlying this variability remain unclear. In this paper, we focus on the role of seed external covering structures on germination, particularly the lemma. Seeds of apomictic and sexual biotypes of P. dilatatum were subjected to acid scarification and removal of the lemma to study their germination, imbibition rate and sensitivity to ABA. Seeds without lemma showed higher germination than other treatments in dormant genotypes. We found that the lemma delayed but did not prevent water uptake in any genotype. Comparing sexual biotypes, P. dilatatum subsp. flavescens showed higher lemma-imposed dormancy than P. dilatatum “Virasoro”, and also higher seed dormancy at the caryopsis level. The thickness of the lemma was not different between these biotypes, so this trait did not explain differences in dormancy. Intraspecific variability of seed dormancy in this species may be attributable to the lemma incidence, however differences in the caryopsis component of seed dormancy should be considered.
Highlights
Paspalum dilatatum Poir. is a perennial warm-season grass that has been proposed as a warm-season forage crop in temperate regions, but like most wild perennial grasses, establishment is too slow for commercial adoption
We studied the germination response and sensitivity to Abscisic acid (ABA) of different P. dilatatum genotypes, emphasizing the sexual biotypes Flavescens and Virasoro, in recently harvested and after-ripened seeds subjected to the extraction of the lemma or acid scarification
In the ABA sensitivity assays, for seeds with one month of storage and the testing conditions assayed (7 d at 20 °C + 14 d at 32 °C), germination ratio (Gtot) without ABA was higher in WOL seeds of Flavescens compared to control seeds (p < 0.05), but no differences between seed coat treatments were found for Virasoro (Figure 3A)
Summary
Paspalum dilatatum Poir. is a perennial warm-season grass that has been proposed as a warm-season forage crop in temperate regions, but like most wild perennial grasses, establishment is too slow for commercial adoption. When ABA is added to germination substrates, it inhibits seed germination by limiting embryo potential growth (FinchSavage and Leubner-Metzger, 2006) Both in domesticated and wild grass species, non-dormant genotypes or seeds with lowered seed dormancy – achieved by stratification or afterripening – exhibit a higher germination response to increasing exogenous ABA levels, i.e. less sensitivity to ABA (Romagosa et al, 2001; Gianinetti and Vernieri, 2007; Goggin et al, 2009; Mares and Mrva, 2014). We studied the germination response and sensitivity to ABA of different P. dilatatum genotypes, emphasizing the sexual biotypes Flavescens and Virasoro, in recently harvested and after-ripened seeds subjected to the extraction of the lemma or acid scarification. We studied water uptake dynamics for each treatment and basic physical characteristics of the lemmas that could be associated with the germination response of each genotype
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