Phosphorus-solubilizing fungi improve growth and P nutrition in sorghum at variable salinity levels

Salt-tolerant phosphorus solubilizing fungi (PSF) play a pivotal role in plant growth promotion and P-nutrition in saline agro-ecoregions. Isolation and characterization of salt-tolerant fungi with P-solubilizing potential and plant growth promotion of sorghum at different salinity levels were conducted.

The best PSFs with inherent salt-tolerance were identified as Penicillium oxalicum (PO), Talaromyces islandicus 1 (Tal1), Talaromyces islandicus 2 (Tal2), Penicillium canescens (PC), and Penicillium setosum (PS). The PO demonstrated the highest salt-tolerance at 2% NaCl concentration. The P and Zn solubilization, ammonia, HCN, siderophore and IAA production were 1.1-10.5 times greater for the PO. The ascorbic and butyric acids were the most abundant organic acids in growth media for Tal1 and other PSF. The fungal mycelium grown on the media supplemented with tricalcium phosphate (TCP) contained 3.3-3.9 times greater P content than the mycelium from the growth medium without TCP (0.44-0.98%). The acidolysis-related genes (pqqC, gcd) and enzymolysis-related genes (phoD, ppk) in salt-tolerant fungal cultures were also present. The fungal inoculated sorghum roots had 3.8-11.0 times greater P-content than uninoculated roots. The siderophore, ammonia, HCN, organic acid and phosphatase secretion explained ~ 46-47% variability in the PSF inoculation responsiveness of P pools and plant parameters to PSF inoculation. The responsiveness of the Olsen's-P, aboveground biomass, and P uptake were strongly correlated with siderophore, ammonia, HCN and organic acid production by the PSF.

This study concludes that augmenting the rhizospheric assemblage of the crops with PSFs having inherent salinity tolerance can be an agronomically sound option to improve the salinity- tolerance and P-nutrition under salt-affected soils.