GERMINACIÓN, VIGOR, VIABILIDAD, CALIDAD Y MEJORA DE SEMILLAS DE CEBOLLA (ALLIUM CEPA L.)

In this work, it has been attempted to improve the value of a non-commercial seed lot of an onion (Allium cepa L.) local variety from Galicia, Spain. Different seed conditioning treatments have been done: prehydration, osmotic and matrix priming, hormonal and disinfection treatments. A densimetric seed separation has been carried out to divide the seed lot in four sublots of different quality and to measure seed answers to hormonal treatments.
Moreover, a tetrazolium seed test was carried out to determine the causes of the seed lot low germination rate.
In the prehydration essay, seeds were immersed in a circulating water flow from 30 minutes to 24 h. Best results were obtained with the 4 h hydration. Prehydration influences micro-organisms contamination percentage of non-germinated seeds. Furthermore, prehydration was combined to a disinfection using sodium hypochlorite 4 % for 4 minutes. Disinfected seeds lost germination capacity.
Hormonal treatment consisted in hydrating seeds on filter paper of different GA3 concentration solutions during germination test. GA3 improved germination uniformity but not germination percentage. Best results have been obtained with the 10 mg•L-1 GA3 concentracion.
In seed separation, differences in germination rate and vigour have been observed in function of seeds medium weight. Seeds were separated in a vertical air flow that divided seeds in four fraction of growing density. A linear correlation between seed germination percentage and one hundred seeds medium weight was determined. It’s possible to separate seeds in different seed sublots of different quality.
Osmotic conditioning were done with deionized water, KNO3 0,1 and 0,3 M and 150, 250 and 350 g•kg-1 PEG-6000 solutions for periods of 24, 48 and 96 h. In PEG-6000 seed osmoconditioning, a significant loss of germination was observed. Deionized water and KNO3 solutions improved seed quality, improving seed germination velocity and uniformity. It has been detected that seed germination uniformity only depends on the period of treatment but not on the solution concentration.
Matrix seed priming gave best results with most deteriorated seeds, improving significantly their germination rate but had a few influence on seeds of better quality. Best treatment resulted the one using the proportion in volume seed: matrix: water of 1:10:2 of Algalita® during 6 days.
In the viability test, a incomplete maturation of seeds was observed and 52,5 % of seeds were viable, with germination results of 45 % on date of viability test. Cotyledons of 38,5 % of seeds were inmature and 12,5 % of seeds didn’t have any embryo. Low maturation of seeds must have been the cause of the low lot quality.