Improved micropropagation and hardening responses in red pepper by ACC deaminase producing Methylobacterium oryzae CBMB20

The effect of plant growth regulators and Methylobacterium oryzae CBMB20 treatment on the growth and stress responses of red pepper was evaluated under in vitro and green house conditions. The highest increase (50%) in wet weight of 1279.2 mg explant^− 1 and dry weight of 37.9 mg explant^− 1 was observed with the combination of 6-Benzylaminopurine (BAP) and Indole-3-butyric acid (IBA) treatment. Among the different combinations tested, BAP + 2,4-Dichlorophenoxyacetic acid (2,4-D) treatment showed the highest number of shoots per explant, shoot length, and rooting response. The combination of CBMB20 (M. oryzae CBMB20) and IBA recorded the highest rooting response in red pepper plants. Colonization in xylem vessels by CBMB20 in red pepper plants can be observed based on the electron microscopic photographs. CBMB20-treated red pepper plants recorded less Malondialdehyde (MDA) content (30–43%), less proline content (52 − 43%), and less electrolyte leakage (38–72%), when compared to plants devoid of CBMB20 treatment. CBMB20 inoculated plants recorded less ethylene emission of 27–57%, 1-aminocyclopropane-1-carboxylic acid (ACC) content of 43–47%, and 1-Aminocyclopropane-1-carboxylic acid oxidase (ACO) activity of 23–25% were recorded in micropropagated plants inoculated with CBMB20 compared to the plants without inoculation. CBMB20-treated red pepper plants recorded a higher survivability of 11–18%, when compared to plants without CBMB20 inoculation. CBMB20 treated micropropagated-red-pepper plants showed a 28–30% increase in plant dry weight compared to micropropagated plants with CBMB20 inoculation.