2013 Annual Report
The goal of this castor breeding project is to develop a new variety having increased oil yield. The method of breeding used in this study is recurrent selection, a process of developing a new population based on an existing population. Base population are bulk seeds of Ricinus communis L. cv. Impala purchased from a nursery. The oil content in individual seed was measured non-destructively using a Minispec mq10 nuclear magnetic resonance (NMR) analyzer (Bruker). Selected seeds were germinated and grown in a greenhouse with well controlled environmental conditions, including temperature irrigation and lighting. Initial selection of High Oil-Impala was performed on a base population of 234 seeds. The oil content in the base population ranged from 40.1-57.5% with an average of 50.3%. Top 28 seeds with oil content = 53% were planted in a greenhouse (GH) and mature seeds (or first cycle seeds) were collected. The oil content in the first cycle population ranged from 44.3-58.1% with an average of 53.9%. One striking feature is the shift in the mean of the first population to greater than that of the base population. About 770 seeds from the first cycle population were rescreened for oil content. The top 30 seeds with oil content = 56% were planted in GH and the second cycle seeds were collected. The oil content in the second cycle seeds ranged from 46.6-59.2% with an average of 54.2%. The second population exhibited a small increase of 0.3% in average oil content, indicating the existence of a genetic ceiling.
Field testing was performed on base population (check line) and test seeds (oil content = 55%) from the second cycle population in a research field at University of California-Davis. About 400 seeds of each population were planted in early June 2011 and 2012, respectively, in a plot of 5 rows, with spacing of 5 ft between rows and 2ft between plants. The check and test plot was spaced apart by 8 rows. The field was adequately maintained by weeding and irrigation. During the following two months, both populations had over 95% seed germination and similar healthy growth rate. Environmental conditions, such as temperature, water and fertilizer supplies were measured regularly to ensure an even distribution of these factors among the population. No abnormal growth was observed. Quantitative data are being collected, representing each population’s seed oil content, yield, days to flower and maturity. Mature seeds were harvested between October and November 2011 and 2012, respectively. Compared to the check line, there are no differences in test line on number of seeds produce from each plant, 100-seed weight, days to flowering and maturity. Oil content of about three thousand seeds was analyzed for each population. Seed oil content ranged 32.6-57.5% with an average of 50.6% in 2011 and 34.5-57.6% with an average of 50.8% in 2012. Oil content in test line ranged 39.5-58.4%, averaging 53.8% in 2011, and 38.7-58.9% averaging 53.9% in 2012. The result demonstrates a rapid method to develop castor cultivars with increased oil yield. For cultivar Impala, 3% increase of oil content can be achieved by 2 cycles of recurrent selection. This work is related to Objective 1 of the parent project: Develop germplasm that enables domestic commercial production of natural rubber and ricinoleate by metabolic engineering and conventional breeding.