Improved potassium nutrition retrieves phosphorus-induced decrease in zinc uptake and grain zinc concentration of wheat.

BACKGROUND: The negative effect of soil-applied phosphorus (P) on zinc (Zn) uptake by plants and its concentration in food grains could be a possible reason for low dietary intake of Zn. Likewise, owing to its critical role in plant tolerance to other abiotic stresses, potassium (K) was thought to retrieve P-induced decrease in grain Zn concentration of wheat. To test the above hypothesis, the effect of K application (50 mg kg-1 soil) on Zn concentration in shoot/grains and its shoot-to-grain translocation was studied in wheat (Triticum aestivum L. cv. Galaxy-2013) under low and optimal supply of both P (10 and 50 mg kg-1 ) and Zn (0 and 5 mg kg-1 ). RESULTS: The response of growth parameters and grain yield to optimal Zn, P and K applications indicated that all nutrients were limiting plant growth at low levels. Irrespective of P level, Zn application at optimal rate increased Zn concentration and uptake by straw and grains of wheat. Contrarily, optimal P application decreased Zn concentration but increased Zn uptake by wheat straw. More specifically, combined application of Zn and P at optimal levels decreased Zn concentration in grains from 43 to 32 mg kg-1 compared with optimal Zn application alone. Potassium application to optimal P- and Zn-supplied plants increased remobilization of pre-anthesis straw Zn store to grains by 50% and decreased Zn concentration in straw. Consequently, K application along with optimal Zn and P supply to plants completely retrieved P-induced loss in grain Zn concentration and also increased grain Zn uptake from 891 to 1249 µg per pot without significantly affecting grain yield. CONCLUSION: The K-induced increase in grain Zn concentration is attributed to K-driven higher post-anthesis Zn uptake and remobilization of pre-anthesis straw Zn store to grains. © 2018 Society of Chemical Industry.

Rhizobium alamii sp. nov., an exopolysaccharide-producing species isolated from legume and non-legume rhizospheres.

A group of exopolysaccharide-producing bacteria was isolated from the root environment of Arabidopsis thaliana. The genetic diversity revealed by REP-PCR fingerprinting indicated that the isolates correspond to different strains. 16S rRNA gene sequence analysis showed that the isolates are closely related to the strains Rhizobium sp. YAS34 and USDA 1920, respectively isolated from sunflower roots and Medicago ruthenica nodules. These bacteria belong to the Rhizobium lineage of the Alphaproteobacteria, and the closest known species was Rhizobium sullae. DNA-DNA hybridization experiments and biochemical analysis demonstrated that the nine strains isolated from A. thaliana and Rhizobium strains YAS34 and USDA 1920 constitute a novel species within the genus Rhizobium, for which the name Rhizobium alamii sp. nov. is proposed. The type strain is GBV016(T) (=CFBP 7146(T) =LMG 24466(T)).