Potential use of the bacteria Azospirillum in association with prickly pear cactus

Abstract

The nitrogen fixing bacterium Azospirillum is recognized to synthesize plant growth regulators. This microorganism was found to live associated with prickly pear cactus. Natural Azospirilla populations in Opuntia roots were found to be 11,000 cells per g of fresh root. When Opuntia cladodes were inoculated with a mixture of A. brasilense strains, Azospirilla numbers reached 1 x 10⁶ per g of fresh root. Fresh and dry weights of Opuntia roots were substantially increased by inoculation, 47% and 34% respectively over an uninoculated control. Nitrogen percentage and total N content from roots were also increased by inoculation in 21% and 63%, respectively, over uninoculated cladodes. Root development enhancement of inoculated Opuntia, may lead to a better nutrient uptake and to an improvement of water status of the plant, a fact of great importance for plants growing under semi-arid or arid conditions.