Thermotolerant PGPR consortium B3P modulates physio-biochemical and molecular machinery for enhanced heat tolerance in maize during early vegetative growth

Background Global warming and irregular changes in temperature are a serious threat to plant growth with a significant negative impact on yield. Global maize productivity has decreased significantly due to sudden temperature fluctuations and heat waves especially in the regions severely hit by climate change. Results The current study demonstrates the potential of beneficial bacteria for inducing heat tolerance in maize during early growth. Three Bacillus spp . AH-08, AH-67, SH-16, and one Pseudomonas spp . SH-29 showed the ability to grow and exhibited multiple plant-beneficial traits up to 45 ± 2 °C. At temperatures of 45 and 50 °C, Bacillus sp. SH-16 exhibited upregulation of two small heat shock proteins (HSP) of 15 and 30 kDa, while SH-16 and AH-67 showed upregulation of two large HSP of 65 and 100 kDa. Plant-inoculation with the consortium B3P (3 Bacillus + 1 Pseudomonas spp.) was carried out on six hybrid maize varieties pre-grown at 25 ± 2 ºC. Heat shock was applied to 10-day-old seedlings as: 3 h at 38ºC, 48 h recovery period, and then 48 h at 42ºC. The B3P treatment showed significant improvement in the overall plant growth (plant height, root & shoot fresh & dry weight, root and leaf area) with a higher level of CAT, POD, total chlorophyll, and carotenoids, while low concentration of MDA. A non-significant difference was observed in case of total cell protein and amino acids after B3P-treatment under stress. The expression of HSP1 and HSP18 in Malka and YH-5427 while HSP70 and HSP101 were higher in FH-1046 and Gohar as compared to non-inoculated treatment. Conclusions These findings indicate that heat-tolerant plant-growth promoting rhizobacteria (Ht-PGPR) exert versatile, multiphasic and differential response to improve plant growth and heat-tolerance in different maize varieties during seedling/ early vegetative growth. Subsequent research will be focused on the field evaluation of these PGPR to see the field and yield response of this consortium under natural temperature fluctuations in field.