Effect of endophytic fungus Piriformospora indica and PEG-induced water stress on maximum root growth pressure and elongation rate of maize

Aim We aimed to determine the effect of Piriformospora indica inoculation on maize maximum root growth pressure ( σ max ) and root elongation rate (ER) over a wide range of water potentials. Methods The maximum axial force ( F max ) exerted by the P. indica -inoculated and non-inoculated roots of maize ( Zea mays L. cv. Maxima) seedlings were measured under control (osmotic potential of zero) and PEG-induced water stress (i.e., osmotic potentials of −0.1, −0.2, −0.3 and − 0.4 MPa) conditions. After measuring root diameter ( d ), σ max was calculated by dividing the F max by the corresponding root cross-sectional area. To test the toxicity of PEG-6000 on root growth, the effect of osmotic potentials induced by PEG-6000 on ER was compared with the corresponding matric potentials in two soils. Results The establishment of a mutualistic relationship between maize roots and P. indica exerted a temporary stress on plants leading to greater lag time for force development ( T lag ) and the time to reach F max ( T max ) in inoculated plants. However, root colonization resulted in greater F max , σ max and ER especially under moderate and severe water stresses. Severe water stress decreased σ max , F max , d , T max and ER. Conclusion P. indica inoculation can moderate adverse influences of stressful conditions on growth and elongation of plant roots especially during the initial growth stages by enhancing osmotic adjustment and/or by changing cell wall mechanical characteristics.