Selection of castor with divergent concentrations of ricin and RCA using radial immunodiffusion

One of the most limiting factors in the production of castor (Ricinus communis L.) is the presence of two toxic proteins, ricin and RCA. Ricin and RCA's presence in the endosperm of the seed creates potential health hazards to both producers and processors. The objectives of this research were to determine the range of ricin/RCA concentration in the USDA castor collection and to determine the inheritance of ricin/RCA concentrations in segregating populations.

The 263 accessions from 34 countries of the USDA collection screened for ricin/RCA concentration ranged from 1.9 to 16.0 mg/g. Only 1% of the accessions had ricin/RCA concentrations less than 3.0 or greater than 13.0 mg/g.

In 1994, two accessions from the USDA germplasm collection PI 257 654 and PI 258 368 reported to have low ricin/RCA concentration were crossed with the commercial oil producing cultivar 'Hale'. In 1996, Fg seed were harvested and evaluated to determine inheritance of ricin/RCA concentration using a radial immunodiffusion (RID) assay which utilized ricin specific antibodies. Five of six F^ populations fit a 15:1 (high:low ricin/RCA) phenotypic ratio and five of six F3 populations fit a 55:9 (high:low ricin/RCA) phenotypic ratio. Heterogeneity X^2 for the F^2 and F^3 generations showed that all six segregating populations did not significantly differ in their segregation patterns. Low ricin/RCA content appeared to be controlled by two recessive alleles. Average ricin/RCA concentration of individual Fg plants ranged from 2.1 to 17.9 mg/g and in the F^3 generation ranged from 0.1 to 20.1 mg/g. Use of the RID assay provided an effective method to screen castor lines for divergent concentrations of ricin/RCA. These results will allow development of non-toxic oilseed cultivars and cultivars with extremely high concentrations of ricin/RCA for pharmaceutical production.