Does the routine heat treatment of sugarcane stem pieces for xylem pathogen control affect the nitrogenase activity of an N2-fixing endophyte in the cane?

Abstract

In sugarcane propagation the sett pieces are routinely heated at 50˚C before planting to control the xylem pathogen Leifsonia xyli ssp. xyli. To determine whether this treatment also affects the diazotrophic endophyte, Gluconacetobacter diazotrophicus, found in the intercellular solution of cane parenchyma, cultures of this bacterium were similarly heated. The nitrogenase activity of the heated cultures was monitored by measurement of hydrogen evolution. Activity was destroyed in cultures heated directly at 45 or 50˚C for 2 h. In contrast, when sett pieces were first heated for 2 h at 50˚C, G. diazotrophicus could still be isolated from the intercellular fluid, and these cultures showed considerable nitrogenase activity. There was no difference in leaf nitrogen content of plants grown in nitrogen-poor soil from setts either heated or unheated. It is concluded that the routine heat treatment of sugarcane setts for pathogen control does not totally destroy the nitrogenase activity of the diazotrophic endophyte G. diazotrophicus.