Influence of a genetically modified endophytic bacterium on composition and decomposition of corn residue

Abstract

I have determined whether the presence of an endophytic bacterium alters the chemical properties of inoculated plants and compared decomposition of colonized residues with control residues in soil. Greenhouse-grown corn ( Zea mays L.) plants (18 days old) were inoculated with either the endophytic bacteria Clavibacter xyli subsp. cynodontis (MDE1) or a genetically engineered construction of C. xyli subsp. cynodontis which was transformed by inserting a gene encoding for production of a δ-endotoxin from Bacillus thuringiensis subsp. kurstaki (MDR1.3). Leaves and stalks were harvested at maturity and various chemical and physical properties analyzed. In addition, leaf and stalk residues were incorporated into soil to determine the extent of their decomposition in a 63 day laboratory incubation study. Leaf residues from plants inoculated with MDR1.3 retained significantly more water than did those inoculated with buffer or MDE1. Leaves of inoculated plants contained significantly more C than did stalks of inoculated plants. Soluble proteins were the major contributors to the C content of leaves, whereas, soluble carbohydrates were predominant in the stalks. Inoculation with either MDR1.3 or MDE1 appeared to increase the quantity of N present in all plant parts. During early stages, leaf residues contained more readily decomposable substrates than did stalk residues. Leaves from plants inoculated with buffer decomposed significantly more after 63 days than those from plants inoculated with MDE1 or MDR1.3. In contrast, corn stalks inoculated with MDR1.3 decomposed significantly more than those inoculated with buffer or MDE1. Over the 63 day incubation ca 33% of the corn residues were decomposed. Although the presence of the endophytes, MDE1 and MDR1.3, during plant growth had some influence on chemical and physical properties of the residues, the extent of residue decomposition in soil (CO 2 evolved in 63 days) was not substantially different.