Source and Sink Manipulation Influencing the Seed Weight Distribution and Yield Components of Castor.

Castor (Ricinus communis L.) is an industrial oilseed crop that in previous studies produced around 10% of aborted seeds. Those aborted seeds have regular seed coats, embryos, and size, but they do not accumulate reserves in the endosperm. This experiment studied the effect of source and sink manipulation on seed abortion and plasticity of yield components. Two genotypes of castor (‘AL Guarany’ and ‘BRS Energia’) were raised in 12 L pots in a greenhouse (Texas Tech University, Lubbock, TX), in a completely randomized design with six replications. The treatments consisted of: (i) a source reduction imposed by weekly defoliations that limited the plant to 50% of the leaf area observed in the day the first raceme was launched; (ii) a sink reduction imposed by clipping all the racemes except the first one; and (iii) a control treatment in which neither source nor sink was manipulated. When the sink was reduced, the leaf area increased to 6406cm² compared with 5341 cm² observed in the control plants. The source reduction increased the frequency of aborted seeds to 14.8%, but the sink reduction did not reduce the frequency of aborted seeds (6.7%), compared with the control (4.5%). The sink reduction did not influence the number of seeds in the first raceme. The mean seed weight of the first raceme was equal in all three treatments. The control plants had a higher seed production because they produced additional racemes. The sink-limited plants were not able to adjust the seed number and seed weight to compensate for the clipped racemes. The source and sink manipulation did not influence the seed filling duration which was 71 days on average. We found little plasticity in most yield components corroborating the hypothesis that the number of racemes provides the most plastic yield component in castor plants.