Microflora respiration and sensitivity to hypoxia are instrumental for pericarp-imposed dormancy expression at high incubation temperature in sunflower (Helianthus annuus)

BENECH-ARNOLD, ROBERTO; CONSTANZA DOMINGUEZ; MARIA VERONICA RODRIGUEZ; BATLLA DIEGO

Conferencia; 12th Conference of the International Society for Seed Science; 2017

Dormancy displayed by sunflower achenes cause serious problems to the seed industry. In this crop,dormancy can be imposed by the pericarp. Pericarp-imposed dormancy in sunflower is expressed athigh incubation temperatures (i.e. 30 °C). This embryo-covering tissue is thought to interfere with theentry of oxygen to the embryo (i.e., hypoxia). We used an inbred line and a commercial hybrid, bothdisplaying pericarp-imposed dormancy, to evaluate the effect of different atmospheric oxygenconcentrations combined with different incubation temperatures (12 °C and 30 °C) on i) germination ofachenes and seeds (i.e. without pericarp) in both genotypes and ii) sensitivity to ABA, in seeds of theinbred line. We also attempted to elucidate the nature of the constraint to oxygen diffusion imposed bythe pericarp. Results showed that, in both genotypes, the germination of achenes decreased withincreasing hypoxia at both temperatures. Seeds from the inbred line were very sensitive to hypoxia at30ºC but not so sensitive at 12ºC. Instead, seeds from the commercial hybrid displayed very lowsensitivity to hypoxia at any temperature. Seed sensitivity to ABA in the inbred line also increased withhypoxia and incubation temperature. Oxygen consumption by isolated pericarps was enhanced at 30°C as compared to 12 °C. However, when a phytotherapy treatment (fungicide + antibiotics) was appliedto isolated pericarps from both genotypes incubated at 30 °C, oxygen consumption was reduceddramatically showing that it was mostly due to respiration of pericarp-associated microbiota. Moreover,the phytotherapy treatment increased germination of achenes from the commercial hybrid and theinbred line, strongly suggesting that high oxygen consumption at high incubation temperature due toenhanced microbial respiration limits achene germination even in the commercial hybrid wheresensitivity to hypoxia is so low. In conclusion, although in both genotypes the nature of the constraintto oxygen diffusion appears to be the same (i.e. enhanced microbial respiration with increasedincubation temperature), in the inbred line dormancy expression seems to be driven by anexacerbated sensitivity to hypoxia, whereas in the commercial hybrid, the pericarp arises as a moresevere restraint when incubation is performed at high temperature.