Development of ACCd producer A. brasilense mutant and the effect of inoculation on red pepper plants.

Azospirillum is a plant-growth-promoting bacterium capable of colonizing and promoting growth in numerous crops of agronomic and horticultural significance. The objective of the present study is to develop Azospirillum brasilense CW903- acdS flocculating cells and to test their performance in promoting the growth of red pepper plants grown under salt stress. The flocculating CW903- acd S recorded 12.6, 37.3 and 91.6% higher ACCd activity at 50, 100 and 150 mM NaCl concentrations, respectively, compared to non-flocculating (normal) CW903- acdS cells. The flocculating CW903- acd S recorded 29.8 and 24.5% higher specific growth rates compared to non-flocculating CW903- acdS cells at 100 and 150 mM NaCl concentration, respectively. The flocculating CW903- acd S recorded 29.7 and 24.5% higher production of IAA-like molecule compared to the non-flocculating CW903- acd S at 100 and 150 mM NaCl concentration, respectively. Similarly, 27.5 and 25.7% higher ARA activity was observed with the flocculating CW903- acd S compared to the non-flocculating CW903- acd S type cells at 100 and 150 mM NaCl concentration, respectively. In the pot culture experiment at 50 and 100 mM NaCl concentration, CW903- acd S inoculated pepper plants recorded 9.4 and 4.7% less ethylene emission, when compared to plants inoculated with non-flocculating CW903- acd S cells. At 100 mM NaCl concentration, plants inoculated with flocculating CW903- acd S recorded 27.5% higher dry weight compared to plants inoculated with non-flocculating CW903- acd S cells. This study implied the significance of flocculating CW903- acd S with better stress amelioration and plant growth promotion in red pepper plants grown under salt-affected conditions due to the positive influence of ACCd activity.