SEEDS

Author: ROJO HERNANDEZ CARLOS.
Year: 2004.
University: POLITÉCNICA DE MADRID [www.upm.es].
Place of defense: E.T.S INGENIEROS AGRONOMOS.
Place of preparation: E.T.S. INGENIEROS AGRONOMOS.

Summary: Rainfed sunflower (Helianthus annuus L.) is often affected by water stress in the most critical steps of its cycle. A possible way of avoiding this trouble is the early sowing. Germination advancement prior to sowing can facilitate crop implantation in adverse conditions. It has been studied the effect of the germination advancement of sunflower seeds of cultivars Peredovik and Cargisol by imbibition in water or in a solution of polyethylene glycol with a mean molecular mass of 6 000 units (â0,8 MPa) at 20 ºC, as well as achenes of cv. Peredovik in water at 12 or 20 ºC and in osmotic solutions with a potential of â0,4, â0,8, â1,2 or â1,6 MPa, using polyethylene glycol 6000 or sucrose as osmotic agent. Imbibition intervals have been 1, 2, 4, 8, 16, 48, 72, 96 and 168 h; maximum interval for each potential was set by the beginning of apparent germination during treatment. Treatment effect has been studied on data of the germination test of treated seeds. Germination was conducted at 7,5 ºC for the two cultivars assay and at 12 ºC in all others. Imbibition is faster with less negative potentials and with higher temperature. Imbibition progress is different for each osmotic agent tested; high water contents were reached first with sucrose. Sucrose penetration into seeds was verified, and this fact can explain that difference. Treatment can achieve an advancement in the germination quantified in a reduction of until one third of the mean germination time (from 4,4 days for the 8 control 562 to 2,9 days). Maximum advancement can be obtained with different combinations of potential and treatment duration (72 h at â1,2 MPa or 96 h at â1,6 MPa, for example). Treatments longer than those of maximum effect can reduce advancement and increase losses of viability and frequency of seedling abnormalities. As a general consequence, treatments increase germination dispersion; this effect is less marked for longer treatments. By using the hydrotime concept a integrated meaning of the effect of the different treatments can be achieved, using as a reference water potential a value (â2,4 MPa) showed in bibliography. Index words: sunflower; Helianthus annuus L.; osmoconditioning; poliethylene glycol; sucrose.