Susceptibility of Common and Tepary Beans to Agrobacterium spp. Strains and Improvement of Agrobacterium-mediated Transformation Using Microprojectile Bombardment

To develop an efficient protocol for Agrobacterium -mediated transformation of common bean ( Phaseolus vulgaris L.) and tepary bean ( P. acutifolius A. Gray), we have tested the susceptibility of six genotypes to eight Agrobacterium tumefaciens and two A. rhizogenes strains. The virulence of the Agrobacterium strains was shown to be genotype dependent. In general, the tumors observed on common bean cultivars were larger than those observed on tepary bean cultivars. The A. tumefaciens AT8196 and Ach5 strains and the A. rhizogenes 8196 strain induced the best responses in all genotypes tested. Polymerase chain reaction (PCR) analysis confirmed the presence of T-DNA in tumors derived from inoculation with three A. tumefaciens strains in common beans. Apical meristems of P. vulgaris cv. Jalo were bombarded with tungsten microprojectiles and then inoculated with an A. tumefaciens wild-type strain (Ach5). One month later, the explants showed a high frequency of tumor formation (50% to 70%). Similarly, when bombarded meristems were inoculated with an A. tumefaciens disarmed strain (LBA4404/p35SGUSINT), 44% of them showed substantial sectors of GUS activity, suggesting the expression of introduced gene. The bombardment/ Agrobacterium system appears to be a promising method to stably transform bean through the regeneration of plants directly from transformed apical meristems.