Gibberellin, Priming, Storing Time, and Other Factors Influencing Castor Seed Germination, Emergence, and Initial Growth

Castor (Ricinus communis) is cultivated for the oil extracted from its seeds for use in the fine chemical industry worldwide. The establishment of castor fields is critical because its emergence is slow and uneven, and this is a challenge as the crop is increasingly culti-vated at large scale in intensive systems. A series of experiments was made for investigat-ing factors and treatments that influence castor emergence aiming to support techniques to improve castor’s agronomic practices. The emergence rate was not influenced by the direction that the seed was placed in the soil. The promoting effect of gibberellin was not reduced when the sowing time was up to 9 days after the seed treatment, and that hor-mone was effective at suboptimal temperature (22 °C). Pre-germination of castor seed fol-lowed by oven drying (45 °C) did not promote faster or higher emergence rate. Castor seeds treated with very high doses had no signs of deformation or atypical development, and there was no evidence that gibberellin applied on the seed had a residual effect caus-ing stem elongation or changes on the seedling’s biomass allocation, although it increased the plant’ sensitivity to shade. Castor seed had slow emergence just after harvesting, and the dormancy was gradually reduced when the seed was stored, but it can also be allevi-ated with gibberellin. The seed required 9 months of storage to alleviate the post-harvest dormancy and reach 90% of the maximum emergence rate. Gibberellin improved signifi-cantly the emergence profile of two out of four varieties at field conditions. A castor line previously selected in vitro for quick germination was confirmed to emerge faster at field conditions, but its initial biomass growth was negatively affected.