Abstract
Salinity is abiotic stress that inhibits seed germination and suppresses plant growth and root development in a dose-dependent manner. Fusarium pseudograminearum (Fg) is a plant pathogen that causes wheat crown rot. Chemical control methods against Fg are toxic to the environment and resistance has been observed in wheat crops. Therefore, an alternative approach is needed to manage this devastating disease and the effects of salinity. Our research focused on the mycoparasitic mechanisms of Trichoderma longibrachiatum (TG1) on Fg and the induction of defenses in wheat seedlings under salt and Fg stress at physiological, biochemical and molecular levels. The average inhibition rate of TG1 against Fg was 33.86%, 36.32%, 44.59%, and 46.62%, respectively, in the four NaCl treatments (0, 50, 100, and 150 mM). The mycoparasitic mechanisms of TG1 against Fg were coiling, penetration, and wrapping of Fg hyphae. In response to inoculation of TG1 with Fg, significant upregulation of cell wall degrading enzymes (CWDEs) was observed. The expression of β-1, 6-glucan synthase (PP4), endochitinase precursor (PH-1), and chitinase (chi18-15) increased by 1. 6, 1. 9, and 1.3-fold on day 14 compared with day 3. Wheat seedlings with combined TG1 + Fg treatments under different NaCl stress levels decreased disease index by an average of 51.89%; increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity by an average of 38%, 61%, and 24.96%, respectively; and decreased malondialdehyde (MDA) and hydrogen peroxide (H2O2) content by an average of 44.07% and 41.75% respectively, compared with Fg treated seedlings. The combined TG1 + Fg treatment induced the transcription level of plant defense-related genes resulting in an increase in tyrosin-protein kinase (PR2), chitinase class I (CHIA1), and pathogenesis-related protein (PR1-2) by an average of 1.15, 1.35, and 1.37-fold, respectively compared to Fg treatment. However, the expression levels of phenylalanine ammonia-lyase (PAL) increased 3.40-fold under various NaCl stresses. Our results suggest that TG1 enhances wheat seedling growth and controls wheat crown rot disease by strengthening the plant defense system and upregulating the expression of pathogenesis-related genes under both Fg and salt stress.
Highlights
Wheat (Triticum aestivum L.) is one of the most important cereals grown in arid and semi-arid regions, providing 20% of the total dietary calorie and proteins intake that promotes human nutrition and healthy living (Shiferaw et al, 2013)
Primers used in the experiments were designed using Primer Express 3.0 software, which amplifies target genes according to the sequences of candidate proteins available in NCBI wheat EST (Wang et al, 2014)
Our results suggest that T. longibrachiatum TG1 is a plant growth-promoting fungus that can tolerate salt stress and control F. pseudograminearum in vitro and in vivo, and induce salinity tolerance of wheat seedlings by attenuating the negative effects of pathogen and salt stress
Summary
Wheat (Triticum aestivum L.) is one of the most important cereals grown in arid and semi-arid regions, providing 20% of the total dietary calorie and proteins intake that promotes human nutrition and healthy living (Shiferaw et al, 2013). Fusarium infections, including Fusarium foot rot (FFR) and Fusarium root rot (FRR), are responsible for outbreaks of seedling blight, epidemic scab, and Fusarium head blight (FHB) in the United States (Subedi et al, 2007) They directly or indirectly cause millions of dollars of losses in wheat and barley production (El-Allaf et al, 2001). Plantgrowth-promoting microbes (PGPM) have several potentials that enable them to enhance plant growth These include ability to fix atmospheric nitrogen and dissolve phosphate in soil, production of siderophores for iron extraction, ACC deaminase that contributes to stress tolerance, and production of indole-3-acetic acid (IAA). They indirectly promote plant growth by the combating pathogens through nutrient and space competition, secretion of antibiotic substances and induction of defense systems in the plant
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