Contribution of BNF by Azoarcus sp. BH72 in Sorghum vulgare

Sorghum vulgare cv. beefbuilder was inoculated in vitro with the diazotrophic bacterium Azoarcus sp. BH72. The aim was to introduce the microorganism into a tropical cereal plant other than the original host plant Kallar grass (Leptochloa fusca (L.) Kunth), which is grown in Pakistan. After 14 days of growth in a climate chamber bacteria were re-isolated from the washed shoot, and then after 19 days from surface sterilized roots indicating, that they had penetrated the root tissue. To evaluate the contribution of biological nitrogen fixation (BNF) by Azoarcus the total nitrogen content in the whole system was analyzed. After 28 days of cultivation we measured a 7-fold increase of total N, from which the majority (72.6%) was located in the growth medium. Using the 15N-isotope dilution method we found that 10.7% of N in the shoot and 2.0% of N in the root derived from atmospheric nitrogen.