Enhancement of Seawater Stress Tolerance in Barley by the Endophytic Fungus Aspergillus ochraceus

Abstract

Symbiotic plant-fungi interaction is a promising approach to alleviate salt stress in plants. Moreover, endophytic fungi are well known to promote the growth of various crop plants. Herein, seven fungal endophytes were screened for salt tolerance; the results revealed that Aspergillus ochraceus showed a great potentiality in terms of salt tolerance, up to 200 g L^-1. The indole acetic acid (IAA) production antioxidant capacity and antifungal activity of A. ochraceus were evaluated, in vitro, under two levels of seawater stress, 15 and 30% (v/v; seawater/distilled water). The results illustrated that A. ochraceus could produce about 146 and 176 µg mL^-1 IAA in 15 and 30% seawater, respectively. The yield of IAA by A. ochraceus at 30% seawater was significantly higher at all tryptophan concentrations, as compared with that at 15% seawater. Moreover, the antioxidant activity of ethyl acetate extract of A. ochraceus (1000 µg mL^-1) at 15 and 30% seawater was 95.83 ± 1.25 and 98.33 ± 0.57%, respectively. Crude extracts of A. ochraceus obtained at 15 and 30% seawater exhibited significant antifungal activity against F. oxysporum, compared to distilled water. The irrigation of barley plants with seawater (15 and 30%) caused notable declines in most morphological indices, pigments, sugars, proteins, and yield characteristics, while increasing the contents of proline, malondialdehyde, and hydrogen peroxide and the activities of antioxidant enzymes. On the other hand, the application of A. ochraceus mitigated the harmful effects of seawater on the growth and physiology of barley plants. Therefore, this study suggests that the endophytic fungus A. ochraceus MT089958 could be applied as a strategy for mitigating the stress imposed by seawater irrigation in barley plants and, therefore, improving crop growth and productivity.

Keywords: Aspergillus ochraceus; barley plants; endophytes; fungal endophytes; plant growth regulation; salinity.

Figure 1

IAA production by A. ochraceus at different levels of salinity. Different letters indicate significant differences between the treatments according to an LSD test at p < 0.05.

Figure 2

Antioxidant activity of the crude extract of A. ochraceus cultured on different levels of salinity. Different letters indicate significant differences between the treatments according to an LSD test at p < 0.05.

Figure 3

Inhibition zones caused by the crude extracts of A. ochraceus cultured at different levels of salinity (0, 15, and 30% seawater) against F. oxysporum.

Figure 4

Effect of seawater irrigation, A. ochraceus application, and their interactions on the morphological parameters of barley plants {(A) shoot length, (B) root length, (C) shoot fresh weight, (D) shoot fresh weight, (E) root fresh weight, (F) root dry weight, and (G) number of leaves}. Each bar represents the mean ± standard error. Different letters indicate significant differences between the treatments according to an LSD test at p < 0.05.

Figure 5

Effect of seawater irrigation, A. ochraceus application, and their interactions on leaf pigments of barley plants {(A) chlorophyll a, (B) chlorophyll b, (C) chlorophyll a + b, and (D) carotenoids}. Each bar represents the mean ± standard error. Different letters indicate significant differences between the treatments according to an LSD test at p < 0.05. FW: fresh weight.

Figure 6

Effect of seawater irrigation, A. ochraceus application, and their interactions on the activity of antioxidant enzymes of barley plants {(A) POD, (B) SOD, and (C) PPO}. Each bar represents the mean ± standard error. Different letters indicate significant differences between the treatments according to an LSD test at p < 0.05. FW: Fresh weight.

Figure 7

Effect of seawater irrigation, A. ochraceus application, and their interactions on the contents of (A) malondialdehyde (nmol g⁻¹ FW) and (B) hydrogen peroxide (mg g⁻¹ FW) in barley plants. Each bar represents the mean and standard error. The letters indicate significant differences between the treatments according to an LSD test at p < 0.05. FW: fresh weight.