MICROFLORA RESPIRATION AND SENSITIVITY TO HYPOXIA ARE INSTRUMENTAL FOR PERICARP-IMPOSED DORMANCY EXPRESSION AT HIGH INCUBATION TEMPERATURE IN SUNFLOWER (Helianthus annuus)
Benech-Arnold, R.L.1,2, Dominguez, C.P.1,2*, Rodriguez, M.V.2 and Batlla, D.2,3
1Universidad de Buenos Aires. Facultad de Agronomía. Departamento Producción Vegetal. Cátedra de Cultivos Industriales. Av. San Martín 4453, C1417DSE, Ciudad de Buenos Aires, Argentina
2Instituto de Fisiología y Ecología Vinculado a la Agricultura, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires (IFEVA-CONICET-UBA). Av. San Martín 4453, C1417DSE, Ciudad de Buenos Aires, Argentina
3Universidad de Buenos Aires. Facultad de Agronomía. Departamento Producción Vegetal. Cátedra de Cerealicultura. Av. San Martín 4453, C1417DSE, Ciudad de Buenos Aires, Argentina
Contact: *C.P. Dominguez, email@example.com
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 at high incubation temperatures (i.e. 30 °C). This embryo-covering tissue is thought to interfere with the entry of oxygen to the embryo (i.e., hypoxia). We used an inbred line and a commercial hybrid, both displaying pericarp-imposed dormancy, to evaluate the effect of different atmospheric oxygen concentrations combined with different incubation temperatures (12 °C and 30 °C) on i) germination of achenes and seeds (i.e. without pericarp) in both genotypes and ii) sensitivity to ABA, in seeds of the inbred line. We also attempted to elucidate the nature of the constraint to oxygen diffusion imposed by the pericarp. Results showed that, in both genotypes, the germination of achenes decreased with increasing hypoxia at both temperatures. Seeds from the inbred line were very sensitive to hypoxia at 30ºC but not so sensitive at 12ºC. Instead, seeds from the commercial hybrid displayed very low sensitivity to hypoxia at any temperature. Seed sensitivity to ABA in the inbred line also increased with hypoxia 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 applied to isolated pericarps from both genotypes incubated at 30 °C, oxygen consumption was reduced dramatically 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 the inbred line, strongly suggesting that high oxygen consumption at high incubation temperature due to enhanced microbial respiration limits achene germination even in the commercial hybrid where sensitivity to hypoxia is so low. In conclusion, although in both genotypes the nature of the constraint to oxygen diffusion appears to be the same (i.e. enhanced microbial respiration with increased incubation temperature), in the inbred line dormancy expression seems to be driven by an exacerbated sensitivity to hypoxia, whereas in the commercial hybrid, the pericarp arises as a more severe restraint when incubation is performed at high temperature.