Redesign of the castorbean plant body plan for optimal combine harvesting

The seed oil of castorbean (Ricinus communis, Euphorbiaceae) is highly appreciated in several sectors of the chemical industry. A tropical perennial, with sympodial branching, this plant presents, at the same time, both vegetative shoots and inflorescences, as well as racemes with ripe seeds. This architecture is an obstacle to harvesting the plants using the standard combine harvester which requires, as with any other seed crop, that the plants be dry. One agronomic solution is to spray the plants with desiccants. However, in this paper a genetic solution is suggested, that is, an 'annual plant'. This model is discussed within the present knowledge of plant monocarpic senescence. A mutation that changes the quantity and/or the quality of cambial activity could reduce the secondary growth in castorbean, thus favouring the plant's death. Moreover, to stop iterative growth which is at the base of the perennial form of castorbean, a non-branching model is also proposed. The occurrence of this phenotype in some crops (maize and sunflower) and mutants (tomato, barley, etc.) is examined. Considering apical dominance as the primary mechanism at the base of a non-branching form, a mutation capable of inducing permanent dormancy of axillary buds is discussed. Both mutation breeding and genetic engineering are suggested as major tools to obtain an annual plant of castorbean.