Field Performance of Clavibacter xyli subsp. cynodontis Expressing the Insecticidal Protein Gene cryIA(c) of Bacillus thuringiensis against European Corn Borer in Field Corn

The field efficacy of the endophytic bacterium Clavibacter xyli subsp. cynodontis (Cxc) expressing the cry-IA(c) insecticidal protein gene of Bacillus thuringiensis (Bt) was evaluated against European corn borer (Ostrinia nubilalis) (ECB) in field corn during 1990 in Maryland and during 1991-1993 in Nebraska. The engineered strains, referred to as Cxc/Bt, were introduced into corn seedlings using a would inoculation technique or into corn seed via a pressure infiltration technique. Two Cxc/Bt strains (MDR1.586, MDR1.1413) were evaluated in the pedigree LH119 × LH82. Plants were artificially infested near pollen shed with neonate ECB larvae and later dissected to determine the amount of ECB tunneling. In 1993, plots were machine-harvested to obtain yield data. Both Cxc/Bt strains significantly reduced ECB damage compared with plants colonized by wild-type Cxc and/or uncolonized control plants. In 1990, strain MDR1.586 reduced the number of tunnels by 64.0%. Field efficacy of strain MDR1.586 was further demonstrated in 1991 and 1992 as treated plants exhibited 57.1 and 65.0% fewer tunnels, respectively. Strain MDR1.1413 reduced the number of tunnels by 79.0% in 1992 and by 68.7% in 1993. Despite the significant control of ECB by strain MDR1.1413 in 1993, grain yield from Cxc/Bt-inoculated plants was not significantly different from the uninoculated control.