Comparison of Benefit to Sugarcane Plant Growth and ¹⁵N₂ Incorporation Following Inoculation of Sterile Plants with Acetobacter diazotrophicus Wild-Type and Nif¯ Mutant Strains

Abstract

The ability of the nitrogen-fixing bacterial endophyte Acetobacter diazotrophicus strain PAl5 to enhance the growth of sugarcane SP70-1143 was evaluated in the growth chamber, greenhouse, and field by comparing plants inoculated with wild-type and Nif mutant MAd3A in two independent experiments. The wild-type and Nif mutant strains colonized sugarcane plants equally and persisted in mature plants. In N-deficient conditions, sugarcane plants inoculated with A. diazotrophicus PAl5 generally grew better and had a higher total N content 60 days after planting than did plants inoculated with mutant MAd3A or uninoculated plants. These results indicate that the transfer of fixed N from A. diazotrophicus to sugarcane might be a significant mechanism for plant growth promotion in this association. When N was not limiting, growth enhancement was observed in plants inoculated with either wild-type or Nif- mutants, suggesting the additional effect of a plant growth promoting factor provided by A. diazotrophicus. A 15N2 incorporation experiment demonstrated that A. diazotrophicus wild-type strains actively fixed N2 inside sugarcane plants, whereas the Nif- mutants did not.

Complete genome of the mutualistic, N2-fixing grass endophyte Azoarcus sp. strain BH72

“…Supply of nitrogen derived from fixation of atmospheric N 2 by grass endophytes, such as Gluconacetobacter diazotrophicus and Azoarcus sp. strain BH72, which has been shown to occur in sugarcane 3 and Kallar grass 2 , is a process of potential agronomical and ecological importance.…”

Inoculation of sugarcane with diazotrophic bacteria

“…The reduction in inoculation efficiency with successive harvests may be associated with N depletion in the soil, because some studies showed that inoculation has no influence on BNF in sugarcane (Schultz et al, 2012) and the yield increases after inoculation may be associated with the growthpromoting effects on the plant root system (Sevilla et al, 2001;Saravanan et al, 2007;Videira et al, 2012). In this case, if the benefit of inoculation is related to the increased use efficiency of plant-available soil N and the soil stock of available N decreases as the crops are being harvested, the efficiency of inoculation may decline over the years.…”

“…These results led to the conclusion that inoculation provided other benefits in sugarcane, which may be associated with the action of plant hormones synthesized by diazotrophic bacteria, phosphate and Zn solubilization, N retention and other essential nutrients in the rhizosphere. Sevilla et al (2001), comparing a strain of Gluconacetobacter with a nitrogenase negative (nif) mutant concluded that other factors, aside from BNF, may be responsible for the benefits resulting from inoculation. Several studies show that diazotrophic bacteria may act in promoting plant growth, mainly by changing the morphology of the root system, thus positively influencing the development and productivity of several crops of economic interest (Bashan et al, 2004;Somers et al, 2004).…”

History on the biological nitrogen fixation research in graminaceous plants: special emphasis on the Brazilian experience

“…Similar results were obtained when the inoculation of the strain PAL5 was done in the presence of low amounts of nitrogen fertilizer (Moraes and Tauk-Tornisielo 1997). Proof that G. diazotrophicus fixes nitrogen was demonstrated by inoculation of micropropagated sugarcane plants with wild-type strain PAL5 and its nif minus mutant followed by measurement of 15 N 2 gas incorporated into the plant tissues (Sevilla et al 2001). Recent results have shown that sugarcane derives benefit from inoculation with a mixture of diazotrophic bacteria (Oliveira et al 2002).…”