Recurrent selection for improved oil content in castor bean

Authors: Chen, Grace; Johnson, Kumiko; MORALE, EVA - Former ARS Employee

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 12/17/2018
Publication Date: 12/28/2018
Citation: Chen, G.Q., Johnson, K., Morale, E. 2018. Recurrent selection for improved oil content in castor bean. In: Kole, C., Robinowicz, P. editors. The Castor Bean Genome. Compendium of Plant Genomes. Cham, Switzerland: Springer Nature. p.67-75. https://doi.org/10.1007/978-3-319-97280-0_4.
DOI: https://doi.org/10.1007/978-3-319-97280-0_4

Interpretive Summary: Castor (Ricinus communis) seed oil is currently the only commercial source of hydroxy fatty acid (12-hydroxyoleic acid, 18:1OH) which is used in industrial products such as lubricants, coatings, plastics and cosmetics. Increasing seed oil content has immense benefits as it is one of the major factors contributing to oil yield. This chapter describes an effective procedure to increase oil content through recurrent selection based on screening individual castor seeds using nuclear magnetic resonance technology. We have proven that recurrent selection through screening single seed is an effective method to improve oil content in castor bean. This method should be applicable to commercial castor bean crops.

Technical Abstract: Castor bean (Ricinus communis) is an important oilseed crop in the Euphorbiaceae family. Castor oil contains 90% an uncommon hydroxylated fatty acid, ricinoleic acid (or 12-hydroxyoleic) (Wang et al. 2011). The hydroxy group imparts unique chemical and physical properties that make castor oil a vital raw material for manufacturing numerous industrial products. Improvement of castor bean cultivars by increasing oil content would be of great benefit as it contributes to oil yield and makes the production more cost competitive. A nuclear magnetic resonance (NMR) analyzer can be used to measure the percentage of oil in a living castor bean seed. Each single castor bean seed is weighed and placed in a NMR tube and then measured against a calibration curve to determine oil content. Recurrent selection is performed by the following basic procedures: 1) individual seeds with high oil content are selected from a base population by screening the base population using NMR; 2) selected seeds are planted and a new generation of seeds is produced through open-pollination; 3) the new generation of seeds forms a new population for the next cycle of screening and selection; 4) field tests are performed to evaluate the productivity of the new population. We have proven that recurrent selection through screening single seed is an effective method to improve oil content in castor bean. Two cycles of recurrent selection increased the mean oil content of Impala from 50.33% to 54.47%, reaching levels comparable to those at the top 1% of 1,103 castor bean lines collected by USDA. As a consequent result, we found that seed weight was also increased after recurrent selection and the strong correlation uncovered between seed oil content and weight will allow further improvement of oil content by screening heavier or larger seeds in a population. Given that single seed recurrent selection was successful under field conditions, this method should be applicable to commercial castor bean crops.