EFFECTS OF REGIONAL ORIGIN AND GENOTYPE ON INTRASPECIFIC ROOT COMMUNICATION IN THE DESERT SHRUB AMBROSIA-DUMOSA (ASTERACEAE)

Previous work has shown that the contact inhibition that occurs among roots of Ambrosia dumosa shrubs has a self/nonself recognition capabil ity. In the current study, we investigated some of the geographic and genotypic dimensions of this recognition capability by using root obse rvation chambers to observe the effects of encounters of individual ro ots on root elongation rates. We measured such effects in encounters b etween roots of plants from the same region and compared these to effe cts in encounters between roots of plants from two different regions. We also measured effects of encounters between roots of plants from th e same clones and compared these to effects of encounters of roots of plants from different clones. Roots of plants from the same region (po pulation) showed the usual ''nonself'' precipitous decline in elongati on rates following contact, but when roots of plants from different re gions contacted each other, elongation rates continued unchanged. When roots of separate plants from the same clone contacted each other, th e same ''nonself'' precipitous decline in elongation rates as seen in encounters between roots of plants of different clones from the same r egion occurred. Meanwhile, in these same experiments ''self'' contacts between sister roots connected to the same plants resulted in no chan ges in elongation rates. Thus, differences between individuals from tw o geographically separate populations of Ambrosia dumosa may be suffic ient to thwart the ''nonself,'' population-level recognition of simila rity apparently necessary for contact inhibition. Furthermore, the ''s elf'' recognition mechanism, which precludes contact inhibition betwee n two roots on the same plant, appears to be physiological rather than genetic in nature.