Studies on the expression of somatic crossing over in Glycine max L

Variety T219 of Glycine max L. has spontaneous yellow, dark green and double (yellow-dark green) spots on the leaves of plants of genotype Y 11 y 11 but no such spots are found on leaves of Y 11 Y 11 or y11y11 plants. It was suggested (Vig and Paddock, 1968) that the double spots result from somatic crossing over whereas the two types of single spots primarily originate from chromosomal disturbances.Cold shocks disproportionately increased the frequency of double spots, but ethyl methanesulfonate (EMS) did not do so. However, in most cases of each treatment, the frequency of single spots increased. It is suggested that EMS is not very potent in bringing about somatic recombination whereas cold shocks are. Plants from a sample of seeds of variety L65-1237 that had been harvested in 1968 at Urbana, Illinois, did not express the spotting phenomenon, but plants from seeds harvested in 1969 at Reno did have spots. Application of mitomycin C(MC) to the seeds of this variety as well as of T219 increased the incidence of double spots manyfold indicating that MC can reveal the potential for somatic crossing over in a variety which might not otherwise express it. Soaking dry seeds of L65-1237 in aqueous solutions of MC for intervals as short as 2 hours was found effective in increasing the frequency of double spots. The role of MC in relation to DNA synthesis and somatic crossing over is discussed. Application of the chromosome-breaking agent, claunomycin (DM) was ineffective in causing double spots.