Rhizospheric bacterial diversity: Is it partly responsible for water deficiency tolerance in wheat?

Bacterial diversity plays a key role in agricultural environments and is promising for its potential use in sustainable agriculture. The present study was conducted to assess the influence of moisture stress on bacterial diversity in the rhizoplane of wheat line WL- 1076. Healthy seeds were grown in potted soil maintained at moisture contents equivalent to 133% (L1), 100% (L2), 80%; (L3), and 55% (L4) of field capacity. Soil closely adhering to the roots of the plants was removed at heading, grain filling and maturity stage. For each soil sample, one gram of soil was taken for evaluating bacterial population by cultivation method. Moisture stress caused reduction in the bacterial population from 7.13x108 cfu g-1 (control) to 1.03x108 cfu g-1 (L4: moisture) suggesting that the imposed stress directly affects population dynamics of bacteria in rhizoplane. The population size in normal soil was higher at grain formation stage than at heading or m aturity stage and the same trend observed in soil with different moisture stress levels. Moisture deficit changed markedly the structure of soil bacterial communities. Cluster analysis revealed that bacterial community in rhizoplane was represented by mixed population of nine species Staphylococcus aureus (30%), Bacillus subtilis (25%), Enterobacter aerogenes (11%), Bacillus megaterium (8%), Klebsiella aerogenes (8%), Escherichia coli (6%e), Kluyyera cryocrescens (6%), Providencia rettgeri (3%) and Proteus vulgaris (3%). Staphylococcus aureus (30%) and B. subtilis (25%) were relatively abundant in rhizoplane and generally present at all growth stages and moisture levels, indicating their resistance to water stress. Bacterial diversity in rhizoplane (some of which are known to produce exo-polysaccharides) might have provided optimum moisture to the roots to keep them alive and could thus be partly responsible for water deficiency tolerance in wheat.