Frequency of Cross‐Pollination of Soybeans After Seed Irradiation1

Abstract

Soybean [Glycine max (L.) Merrill] seeds of white‐flowered varieties were irradiated with 0, 5, 10, or 20 k rads of gamma rays and planted in rows bordered by purple‐flowered varieties of the same maturity. Honeybees were kept in the vicinity of the plots during the flowering period. Seedlings grown from seeds harvested from the white‐flowered plants were classified for hypocotyl color. The frequency of outcrossing varied with location, with varieties, and with treatment level of irradiation. Outcrossing in the nonirradiated populations varied from 0.30% to 3.62%. An increase of outcrossing, to as much as 11 to 14% in some cases, was observed in the irradiated soybeans. A mixture of the white‐ and purple‐flowered varieties in the same row increased outcrossing slightly over similar treatments with the varieties in separate rows. Seed treatment with ethyl methanesulphonate (EMS) increased outcrossing about the same as the irradiation. In this study a combination of mutagen‐treated seed plus large honeybee populations did not increase outcrossing over earlier reported frequencies from each used separately.