Scanning electron microscopy indicates Pseudomonad strains facilitate AMF mycorrhization in litchi (Litchi chinensis Sonn.) air-layers and improving survivability, growth and leaf nutrient status

•Co-inoculation of pseudomonad R62 and R81 (PGPR) with Glomus intraradices (AM fungi) was tested at two different stages of litchi air-layering technique.•The process of mycorrhization was enhanced with co-inoculation of these pseudomonad strains.•This co-inoculation treatment reduced the mortality and increased the growth of the litchi air-layers.•The leaf primary (N, P, and K) and micro (Zn, Cu and Fe) nutrient status in the litchi air-layers were also improved under this co-inoculation treatment.•Inoculation after detachment of the air-layers from the mother tree was more productive. The efficacy of two plant growth promoting rhizobacteria (PGPR) viz. Pseudomonas jessenni strain R62 and Pseudomonas synxantha strain R81 was examined for mycorrhization of arbuscular mycorrhizal (AM) fungi (Glomus intraradices), survivability, growth and leaf nutrient status in litchi air-layer system. Therefore, the litchi air-layers were inoculated with PGPR i.e., Pseudomonad strains and AM fungi alone and with combination during the preparation of air-layers on the mother tree and planting of air-layers in root trainers just after detachment of the fresh air-layers from the mother tree. The scanning electron microscopy of the litchi roots indicated that Pseudomonad strains enhanced the process of mycorrhization of AM fungi and accounted near about 11.5 (tree inoculation) to 14.5 (root trainer inoculation) per cent increase in colonization over the sole inoculation of AM fungi in respective air-layers. No sign of mortality in any air-layered plants was noted in PGPR + AM fungi and sole AM fungi inoculated air-layers up to 18 months of growing. Significantly the highest shoot and root dry weight, and root length were recorded in the air-layers inoculated with both PGPR and AM fungi. This co-inoculation of PGPR with AM fungi was also responsible for the significant enrichment of the primary (N, P and K) and micro (Zn, Cu and Fe) nutrient concentration of the leaves in the litchi air-layers. However, the inoculation of air-layers with these microorganisms failed to produce any significant effects on leaf secondary (Ca, Mg and S) nutrient content. Further, the inoculation treatments had an adverse impact on leaf Mn content. The fresh air-layers inoculated after detachment from the mother tree were performed better for most of the studied parameters than the tree inoculated air-layers.