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Natural Outcrossing in Dwarf-Internode Castor, Ricinus communis L.¹

Four groups of spineless (ss) dwarf-internode castor plants derived from the variety ‘Baker 296’ were grown adjacent to or surrounded by normally spined (SS) plants, to determine frequency of natural outcrossing for the High Plains area of Texas. Wind velocity in this region ranges from 8 to 48 km (5 to 30 miles) per hour during the pollinating season. Progenies were classified as sparsely spined (Ss) as follows: ExperimenIt — single row of 20 ss plants, 42.2%; Experiment II — three adjacent rows of 20 ss plants at two locations, 46.3%; ExperimentIII — single ss plants interplanted with SS plants of various lines, 70.5%; and Experiment IV — single ss plants found in experimental plantings and commercial fields, 76.2%

Three of nine progenies in Experiment IV produced over 90% outcrossing, ranging from 54.1 to 100%. This group probably gave the best estimate of percentage outcrossing, as the ss plants were similar in flowering date, size, and genotype to the surrounding SS plants. Natural outcrossing of dwarf-internode castor can well be in the range of 70–90% for the Texas High Plains.

Key Words: Spineless • spined • wind-pollination • open-pollination • pollen • sibbing

² Research Agronomist, Crops Research Division, ARS, USDA.

Received for publication February 1, 1967.