Systematic Investigation of the Effects of Macro-elements and Iron on Soybean Plant Response to Fusarium oxysporum Infection

Abstract

Nutrient manipulation is a promising strategy for controlling plant diseases in sustainable agriculture. Although many studies have investigated the relationships between certain elements and plant diseases, few have comprehensively explored how differing mineral nutrition levels might affect plant-fungal pathogen interactions, namely plant susceptibility and resistance. Here, we systematically explored the effects of the seven mineral elements that plants require in the greatest amounts for normal development on the susceptibility of soybean plants (Glycine max) to Fusarium oxysporum infection in controlled greenhouse conditions. Nitrogen (N) negligibly affected plant susceptibility to infection in the range 4 to 24 mM for both tested soybean cultivars. At relatively high concentrations, phosphorus (P) increased plant susceptibility to infection, which led to severely reduced shoot and root dry weights. Potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), and iron (Fe) induced plant resistance to infection as their concentrations were increased. For K and Ca, moderate concentrations had a positive effect on plant resistance to the pathogen, whereas relatively high doses of either element adversely affected plant growth and promoted disease symptoms. Further experiments were conducted, assessing disease suppression by selected combinations of macro-elements and Fe at screened concentrations, i.e., K (9 mM) plus Fe (0.2 mM), and S (4 mM) plus Fe (0.2 mM). The disease index was significantly reduced by the combination of K plus Fe. In conclusion, this systematic investigation of soybean plant responses to F. oxysporum infection provides a solid basis for future environmentally-friendly choices for application in soybean disease control programs.

Keywords: Fusarium oxysporum; macro-element; plant yield; soybean; susceptibility.

Fig. 1

Soybean–Fusarium oxysporum interactions under normal growth conditions. (A) Soybean plants showed disease symptoms after inoculation for 2 weeks. Scale bars = 3 cm. (B) Effect of F. oxysporum on root rot severity. (C) Effect of F.oxysporum on plant height. (D) Effect of F. oxysporum on shoot dry weight. (E) Effect of F. oxysporum on root dry weight. Bars in B–E panels indicate mean ± standard errors.

Fig. 2

The effect of N supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 3

The effect of P supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 4

The effect of K supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 5

The effect of Ca supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 6

The effect of Mg supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 7

The effect of S supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 8

The effect of Fe supply on soybean plants inoculated with Fusarium oxysporum. (A) Disease severity. (B) Plant height. (C) Shoot dry weight. (D) Root dry weight. Data shown are mean ± standard errors.

Fig. 9

The effect of combination of optimized concentrations of K, S, and Fe supply on soybean plants inoculated with Fusarium oxysporum. Data shown are mean ± standard errors.