Evaluating the plant growth promoting ability of thermotolerant bacteria and cyanobacteria and their interactions with seed spice crops

• Thermotolerant bacteria and Cyanobacteria were evaluated in coriander, cumin and fennel.
• Microbial inoculation stimulated peroxidase and endoglucanase activity.
• Significant enhancement in growth and vigour of plants by microbial fortification.
• Bacillus pumilus and Calothriix elenkinii proved most promising.
• Microbial inoculation can be eco-friendly plant growth promoting options for spice crops.

The potential of eight thermotolerant bacteria (seven Bacillus spp. and one actinobacterium Kocuria sp.) and two cyanobacteria (Anabaena laxa and Calothrix elenkinii) as plant growth promoting (PGP) agents was evaluated with seed spices – coriander, cumin and fennel, under controlled conditions in potting mix fortified with microbial cultures. Amendment with Anabaena brought about 25% enhanced germination in cumin over control, while Calothrix enhanced root/shoot length significantly in all the three crops, especially fennel. Fortification with microbes led to 30–50% increase in shoot/root length, which was reflected as two–three fold enhancement in the vigour index of the plants. Among the bacterial strains, T4 (Bacillus pumilus) was most promising in terms of PGP traits in fennel and cumin crop. Plant dry weight and peroxidase activity of shoots and roots were enhanced by 5–10-folds in all the microbe inoculated treatments, with highest values in Calothrix treated coriander seedlings. β-1,3 endoglucanase activity showed twofold enhancement in shoots from Anabaena inoculated coriander seedlings. The fungicidal activity of the root extracts from the bacteria treated treatments of coriander seedlings against Macrophomina phaseolina was highest, while root extracts of fennel seedlings were able to show largest zones of inhibition against Fusarium moniliforme. This study highlighted the promise of fortification with both heterotrophic and photosynthetic microbes in plant growth promotion, and their significant role in enhancing and eliciting peroxidase/endoglucanase enzyme and fungicidal activity of plant extracts of seed spices.