Changes in physiological quality of encrusted sunflower ( Helianthus annuus L . ) seeds during storage

 Background to the research and aims: Seed encrusting increases weight and reduces variability in seed size through gradual accumulation of layers of adhesive and inert material. This technology ensures great accuracy in sowing of small caliber sunflower seeds and does not have adverse effects on physiological quality of seeds immediately after the treatment is made. However, this response could be modified along postharvest. Reductions in radicle and seedling emergence in encrusted seeds of different species have been detected during storage. So, the aim of this research was to evaluate the effect of encrusting over the percentage and rate of radicle and seedling emergence of sunflower seeds during their storage.  Overview of the methodology used: The treatments applied were: encrusting with talc (T), encrusting with carbonate (C), encrusting with talc + insecticide + fungicide (TIF), insecticide + fungicide (IF). Seeds without any product were considered as control. Insecticide and fungicide were respectively tiametoxan and metalaxyl. Seeds were stored in laboratory conditions for 10 months in paper bags at 60 %RH and 25°C. The trials were performed as described by ISTA (2010) for sunflower. Measures were made at the initial moment of seed encrusting and 3, 5, 8 and 10 months later. Variables considered were: Time required for the emergence of 50% of radicles (G50 h), Final percentage of seeds with emerged radicle (% RE), Speed of seedling emergence index (SSEI), germination percentage (GP) and seedlings dry weight (SDWmg/seedling).  Key results: After 10 months of storage, encrusted seeds showed a significant increase in G50, while %RE decreased only in C and TIF treatments. All treatments expressed and increase in SSEI up to the 5th month of evaluation, decreasing towards the end of the trial. In C treatment, GP was stable during all months of storage, however in control and the rest of treatments this stability was observed only until the 8 th month with significant reduction after that time. SDW were significantly greater in all treatments of encrusted seeds, however IF treatment showed significantly lower values of this variable and GP during the whole period of storage.  Discussion and conclusion: The reduction in radicle emergence rates over time agreed with that found in seeds of different species. Divergences in GP performance of encrusted sunflower seeds in relation to other species are probably due to morphological and biochemical differences among them. Seed encrusting did not exert adverse effects further deterioration caused by aging itself as it was exposed by the similar maintenance of GP till the 8 th month in encrusted and control seeds. Therefore as a primary conclusion it can be said that, for the sunflower hybrid studied, the encrusting process applied after harvest did not affect negatively seed physiological quality along the storage period of 8 months.  The nature of the contribution to current knowledge achieved by the research on which the abstract is based: These findings draws out some critical morphophysiological traits performance that support the analysis of encrusting effect during storage period, allowing to recommend appropriate time to apply this technology.