2017 Volume 61 Issue 1 Pages 40-47
The relationship between nitrogen absorption and growth of lesser yam (Dioscorea esculenta L.) is not clearly understood. The results of our previous experiment that lesser yam was able to grow under poor fertile soil conditions without nitrogen fertilization; however, the source of nutrition was not identified. This study, which was conducted from April 2015 to January 2016 aimed to determine whether nitrogen-fixing endophytic bacteria are associated with lesser yam. Growth with urea (N treatment), with cow manure (CM treatment) and without nitrogen (control) was compared. N and CM treatment had a positive effect on growth and tuber yield in soil with poor organic matter. Control plants presented with yellowish leaves, but grew until harvest and had a tuber yield comparable with other treatments. Changing natural isotope values (δ15N) under N and CM treatment suggested that nitrogen was absorbed from the urea and cow manure, respectively; however, the source of nitrogen in the control plants was not identified. Isolation of nitrogen-fixing endophytic bacteria using an acetylene reduction activity test and phylogenetic analysis of 16S rRNA gene sequences revealed five species of in the stem and roots of the lesser yam plants. These species were shown to be related to species in the genera Azospirillum, Devosia, Klebsiella, Rhizobium and Xanthomonas. The Rhizobium sp. was found in stem and the others were observed in the roots of lesser yam. All these species are known as nitrogen fixing bacteria and associate with plants growth. This is the first report to identify nitrogen-fixing endophytic bacteria associated with lesser yam.
