Phosphite: a novel P fertilizer for weed management and pathogen control

Abstract

The availability of orthophosphate (Pi) is a key determinant of crop productivity because its accessibility to plants is poor due to its conversion to unavailable forms. Weed's competition for this essential macronutrient further reduces its bio-availability. To compensate for the low Pi use efficiency and address the weed hazard, excess Pi fertilizers and herbicides are routinely applied, resulting in increased production costs, soil degradation and eutrophication. These outcomes necessitate the identification of a suitable alternate technology that can address the problems associated with the overuse of Pi-based fertilizers and herbicides in agriculture. The present review focuses on phosphite (Phi) as a novel molecule for its utility as a fertilizer, herbicide, biostimulant and biocide in modern agriculture. The use of Phi-based fertilization will help to reduce the consumption of Pi fertilizers and facilitate weed and pathogen control using the same molecule, thereby providing significant advantages over current orthophosphate-based fertilization.

Keywords: pathogen management; phosphate fertilizer; phosphite dehydrogenase; phosphorus use efficiency; stimulant; weedicide.

Figure 1

Schematic representation of flow of P from source to sink. The figure highlights the distribution, flow and loss of P for every ton (1000 kg) of rock phosphate mined from the underground reserve. The P losses from various points are depicted by red dashed lines. Calculations are based on data from Cordell et al. (2011a).

Figure 2

(a) Global demand of phosphorus in different sectors. (b) Type of phosphorus fertilizer used in agriculture: monoammonium phosphate (MAP), diammonium phosphate (DAP), nitrogen, phosphorus and potassium (NPK), single superphosphate (SSP), triple superphosphate (TSP). Data source from Schröder et al. (2010).

Figure 3

(a) Homodimeric structure of phosphite dehydrogenase protein forms the Pseudomonas stutzeri (strain WM88) in complex with NAD molecule. (b) NAD Pocket Interaction with the amionacids of ptxD protein. (c) Catalytic chemical reaction of ptxD enzyme with phosphite molecule.

Figure 4

Phosphite compound induced defence mechanism in a plant cell. Phosphite inhibits phosphorylation, competes for phosphate binding sites in phosphorylating enzymes and causes alteration of nucleotide pool in the pathogen resulting in disruption of metabolism and growth inhibition. It induces the expression of defensive molecules, such as phytoalexins and pathogen‐related (PR) proteins to block the pathogen directly. These molecules send systemic alarm signals to the noninfected neighbouring cells and induce defensive response mechanisms including cell well modification via deposition of polysaccharides.

Figure 5

Biostimulatory effects of Phi compounds on growth, plant development and fruit quality.

Figure 6

Analysis of postemergent herbicidal action of Phi. (a, b) The figures show the postemergent herbicidal action of Phi before and after foliar application to weeds, WT plants and transgenic rice lines. (Reproduced with permission from Fig. 8 in Manna et al., 2016).

Figure 7

Influence of different levels of Pi or Phi on biomass accumulation in WT and transgenic seedlings. (a) Phi treatment at any level resulted in WT seedling death after 15 days of application. In contrast, the biomass of WT seedling increased P ≤ 0.01 (**) significantly upon Pi supplementation. (b) Both Pi and Phi treatment at all given levels significantly increased P ≤ 0.05 (*) or 0.01 (**) biomass accumulation in ptxD transgenic plant (L‐16) (Reproduced with permission from Fig. 5 in Manna et al., 2016).

Figure 8

Potential advantages of phosphite usage in agriculture.