A combination of Trichoderma harzianum HE23 and Spirulina maxima UTEX LB2342 effectively induces plant immune responses in wheat against yellow rust and promotes the host growth

Abstract

Wheat yellow (stripe) rust is a destructive disease caused by Puccinia striiformis f. sp. tritici that leads to great economic losses. The aim of this study was to evaluate the biocontrol of stripe rust of wheat and promote its growth through the application of Trichoderma harzianum HE23 and/or Spirulina maxima UTEX LB2342 (at 1 and 2 g L⁻¹). In vitro assay revealed the direct antifungal potential of T. harzianum HE23 filtrate and S. maxima aqueous extract (2 g L⁻¹) as they inhibited the P. striiformis f. sp. tritici uredospores germination by 99.16% and 100%, respectively. Gas chromatography/mass spectrometry (GC/MS) analysis of T. harzianum HE23 ethyl acetate extract revealed the existence of forty-six constituents with varying proportions, mainly palmitic acid (34%), stearic acid (22%), and tricosanenitrile (4%) of known antifungal potencies. In the greenhouse, combined spraying of wheat plants with S. maxima extract (2 g L⁻¹) and T. harzianum HE23 filtrate reduced the disease severity to 11.67%. Furthermore, spraying of this combined treatment overexpressed three resistance genes such as JERF3, POD, and CHI II, with varying levels. In addition, this dual treatment enhanced the POD (peroxidase), PPO (polyphenol oxidase), and CAT (catalase) antioxidant enzymes activity in the infected plants, recording 68.23, 17.00, 35.47 Unit min⁻¹g⁻¹ f. wt, respectively. A noticeable increment in phenol contents (86.5%) and a significant decrease in lipid peroxidation (54.9%) were also observed in response to this dual treatment, compared to the unsprayed and infected plants. Moreover, application of this combined treatment promoted the treated wheat plants growth parameters and improved their photosynthetic pigments content, mainly chlorophyll (a, b) and carotenoids, compared to the non-sprayed and infected plants. To our knowledge and for the first time, this study reports the combined application of T. harzianum and S. maxima as ecofriendly bioagents and biostimulants in the greenhouse to manage yellow rust of wheat and promotes its growth.