SOMATIC INSTABILITY IN DERIVATIVES FROM AGROELYMUS TURNERI RESEMBLING AGROPYRON REPENS

NIELSEN, E. L., and J. NATH. (U. Wisconsin, Madison.) Somatic instability in derivatives from Agroelymus turneri resembling Agropyron repens. Amer. Jour. Bot. 48(4): 345-349. Illus. 1961.Variations in somatic chromosome numbers of 4 to over 80 were observed in root tip cells of Agropyron repens-like plants derived from Agroelymus turneri. The latter presumably had outcrossed to Agropyron repens. Split spindles in dividing nuclei and multinucleate cells were observed in the root tip meristem. The nuclear and mitotic behaviors observed can perhaps be attributed to an unbalanced ribonucleoprotein system resulting from the combination of distantly related genomes in the formation of the hybrid. AGROELYMUS TURNERI LePage was described as a naturally occurring intergeneric hybrid between Agropyron smithii Rydb. and Elymus innovatus Beal (LePage, 1952). Some fertility was observed in plants established at Madison, Wisconsin, from clones taken from the type location (Nielsen, 1961a). Cytological studies of these plants strongly indicated that the hybrid was tetraploid (2n= 28). Elymus innovatus is also tetraploid, but Agropyron smithii is octoploid with 2n-56 (Bowden, 1959). From observations made upon these plants developed from seed taken near the type location of the hybrid, it was suggested by Bowden (1959) and Nielsen (1961a) that Agropyron dasystachyum (Hook.) Scribn. (2n_28) may be the Agropyron parent involved in Agroelymus turneri. Three hundred of the 313 seedlings obtained from seed produced by clones from the type colony were grown to maturity at Madison. "Trashy" seed lots were germinated in steam-sterilized soil. All adult plants resulting from this seed lot were morphologically indistinguishable from Agropyron repens (L.) Beauv. Subsequently, other seed collections were obtained from other colonies of Agroelymus turneri growing near the type colony at Fort Saskatchewan, Alberta, Canada. These were handled similarly to the above. Progeny (937) of 26 plants established from seed of one collection was similar to A. repens also. Similarly, a single plant (938-2) in a segregating population was of quackgrass type, whereas other segregants were similar to Elymus canadensis L. and Agropyron dasystachyum, respectively, (Nielsen 1961b). These plant populations constitute the materials upon which this study was based, the object being to determine the nature of variability in somatic chromosome number together with an exploration of the manner in which these variable numbers arise. The occurrence of variable chromosome numbers 1 Received for publication November 9, 1960. Results of cooperative work of the Crops Research Division, A.R.S., U. S. Department of Agriculture, and the Wisconsin Agricultural Experiment Station. 2 Geneticist, Crops Research Branch, A.R.S., U. S. Department of Agriculture, and Graduate Assistant, Department of Agronomy, Wisconsin Agricultural Experiment Station. in somatic tissue within individual plants of a number of plant families has been recorded in extensive citations by Snoad (1955), Hull and Britton (1958), Hedgwood and Haugh (1958), Pohlendt (1959) and Gottschalk (1959) . Additional records have been examined and could be cited. They merely amplify the rather extensive literature already referred to. Related behaviors have been considered elsewhere (Nielsen, 1961b). Somatic instability, manifest in macroscopic variations in plant tissue, has been reported by Sachs (1952), Lefevre and Heslot, (1953), Latterell (1958), Michaelis (1959), and others. Some of this has been associated with cytoplasmic sterility. METHODS.-Unstable chromosome numbers were found to characterize 3 plants (R8-20, R12-2 and R14-3) examined of the 300 developed from the Madison population of Agropyron repens-like individuals. Since these plants were badly intergrown when this condition was determined, the subsequent Fort Saskatchewan population was grown at 4-ft. spacings in nursery plantings established during late June, 1958. On September 16, whole rhizomes were carefully removed from nursery-grown plants. Care was taken to secure the entire underground stem from its tip to the mother plant from which it arose. Individual nodes having a single bud and the adjacent internodes were planted in 4-in. earthenware pots. These were maintained under greenhouse conditions until the summer of 1959 when they were transplanted into the field on July 3-4. Each rhizome and node sampled was assigned an arbitrary number that depended upon its position in relation to the mother plant. For example, 938-2(M) indicated that this clone was developed from a node taken from the center of the original plant established in the field. Similarly, 938-2(31) indicates that at least 3 rhizomes of this plant were sampled and the second digit indicates that this clone was developed from the node nearest the original plant sampled, i.e., node no. 1. At least 5 nodes separated those sampled of a given rhizome. During mid-October, 1959, rhizomes were again removed from the nursery plantings, washed, and wrapped tightly in paper toweling soaked in an