IMPROVEMENT OF TRANSGENIC ALFALFA BY BACKCROSSING

Two regenerative alfalfa genotypes were transformed with Agrobacterium tumefaciens with binary vectors containing the coding sequences for b eta-glucuronidase (GUS) and npt II (kanamycin resistance), The regener ative genotypes and their transgenic populations were agronomically in ferior, and one was a somaclonal variant for flower color. GUS was use d as a dominant genetic marker in a model system for studying backcros sing to improve transgenic alfalfa. Agronomic yield deficiencies and s omaclonal changes were corrected by one to three backcrosses to cultiv ar genotypes, depending on the vigor of the original transformant. Thr ee backcrosses were considered optimal because progeny contain 94% cul tivar germplasm and could be used as parents of a new cultivar. Use of different cultivar genotypes each generation of backcrossing minimize d inbreeding and maximized the heterotic potential of backcross deriva tives. The improvement of transgenic alfalfa by backcrossing using a d ominant marker required only as much time as the original transformati on experiment.