Cold stress alleviation using individual and combined inoculation of ACC deaminase producing microbes in Ocimum sanctum

Abstract

Cold stress in Ocimum sanctum is a major constraint to crop productivity in certain geographical regions. The current study was carried out to examine the effect of consortia of ACC deaminase producing microbes in reducing cold-induced damage in O. sanctum during winters to enable farmers to have O. sanctum as multi-cut crop. The effect of single and combined inoculation of ACC-deaminase producing four plant growth promoting bacteria (PGPB) including Brevibacterium halotolerans (Sd-6), Bacillus subtilis (Ldr-2), Achromobacter xylosoxidans (Fd-2) and Burkholderia cepacia (Art-7), and a biocontrol agent Trichoderma harzianum (Th) have been investigated. Inoculation of O. sanctum plant with Th+Fd-2 showed better photosynthetic efficiency, which could have resulted in enhanced fresh herb weight (83.78%), compared to un-inoculated control plants. Moreover, the inoculation of Th +Fd-2 improved the nutrient uptake, increased the accumulation of proline, starch, total phenolics, and reduced the accumulation of ACC (1-aminocyclopropane-1-carboxylic acid), a direct precursor for ethylene biosynthesis. Scanning electron microscopy showed the effective co-colonization of Th with Fd-2 on the root surface. Our results suggest that co-inoculation of Th+Fd-2 could be a green initiative that can improve plant growth and alleviate cold stress-induced damages in O. sanctum.