Can Azospirillum strains capable of growing at a sub-optimal temperature perform better in field-grown-wheat rhizosphere

Two Azospirillum brasilense strains, CDJA and A40, capable of growing and producing plant growth-promoting (PGP) substances at the sub-optimal temperature (SOT) of 22°C, were tested for their ability to survive, colonize and enhance wheat growth and yield under field conditions upon inoculation. The response was compared with that of A. brasilense strain, A9, impaired in growth and PGP activities at SOT (22°C) but otherwise comparable to CDJA and A40 at 37°C. A field experiment was carried out in a split-plot design with four levels of N as main plots and three strains and an uninoculated control as subplots. A differential response in the establishment of the strains and in plant growth and yield was obtained, due to the categories of strains, particularly at lower levels of N (0 kg and 40 kg N ha^-1). The results clearly demonstrated that strains capable of growing and producing PGP substances at SOT are better inocula for wheat.