Fusarium Head Blight Infection Induced Responses of Six Winter Wheat Varieties in Ascorbate-Glutathione Pathway, Photosynthetic Efficiency and Stress Hormones

Abstract

Fusarium head blight (FHB) is one of the most studied fungal diseases of wheat, causing massive grain yield and quality losses. This study aimed to extend previous studies on the physiological and biochemical responses of winter wheat to FHB stress in a controlled environment by focusing on the ascorbate-glutathione pathway (AsA-GSH), photosynthetic efficiency, and stress hormone levels, thus providing insight into the possible interactions of different defense mechanisms during infection. The activity of AsA-GSH metabolism was increased in FHB resistant varieties, maintaining the redox state of spikes, and consequently preserving functional photosystem II. Furthermore, carotenoids (Car) were shown to be the major pigments in the photosystem assembly, as they decreased in FHB-stressed spikes of resistant and moderately resistant varieties, compared to controls. Car are also the substrate for the synthesis of abscisic acid (ABA), which acts as a fungal effector and its elevated content leads to increased FHB susceptibility in inoculated spikes. The results of this study contributed to the knowledge of FHB resistance mechanisms and can be used to improve the breeding of FHB resistant varieties, which is considered to be the most effective control measure.

Keywords: AsA-GSH cycle; FHB; abscisic acid; photosynthetic efficiency; salicylic acid; wheat.

Figure 1

Fusarium head blight (FHB) symptoms of the spike bleaching in variety Golubica (a), Tika Taka (b), El Nino (c), Kraljica (d), Galloper (e), and Vulkan (f) at 10 days post inoculations (dpi).

Figure 2

Content of (a) reduced glutathione (GSH) and (b) oxidized glutathione (GSSG) in the control and FHB-stressed spikes of six winter wheat varieties (Golubica, Tika Taka, El Nino, Kraljica, Galloper, and Vulkan). Bars represent mean values of six independent biological replicates ± SD. Different letters indicate significant difference among treatments in each variety separately (p < 0.05).

Figure 3

The activity of (a) ascorbate peroxidase (APX), (b) monodehydroascorbate reductase (MDHAR), (c) dehydroascorbate reductase (DHAR), and (d) glutathione reductase (GR) in control and FHB-stressed spikes of six winter wheat varieties (Golubica, Tika Taka, El Nino, Kraljica, Galloper, and Vulkan). Bars represent mean values of six independent biological replicates ± SD. Different letters indicate significant difference among treatments in each variety separately (p < 0.05).

Figure 4

Content of chlorophyll a (Chl a) (a), chlorophyll b (Chl b) (b), carotenoids (Car) (c), chlorophyll a/b ratio (Chl a/Chl b) (d), and carotenoids/total chlorophyll ratio (Car/Chl a + Chl b) (e) in control and FHB-stressed spikes of six winter wheat varieties (Golubica, Tika Taka, El Nino, Kraljica, Galloper, and Vulkan). Bars represent mean values of six independent biological replicates ± SD. Different letters indicate significant difference among treatments in each variety separately (p < 0.05).

Figure 5

Maximum quantum yield of primary photochemistry (TR₀/ABS) in control and FHB-stressed spikes of variety Golubica (a), Tika Taka (b), El Nino (c), Kraljica (d), Galloper (e), and Vulkan (f). Bars represent mean values of six independent biological replicates ± SD. Different small letters indicate significant difference between treatments at each measurement point separately (1 day post inoculation (dpi), 3 dpi, 7 dpi, and 10 dpi) (p < 0.05). Different capital letters indicate difference among measurement points in each treatment separately (p < 0.05).

Figure 6

Performance index on absorption basis (PI_abs) in control and FHB-stressed spikes of variety Golubica (a), Tika Taka (b), El Nino (c), Kraljica (d), Galloper (e), and Vulkan (f). Bars represent mean values of six independent biological replicates ± SD. Different small letters indicate significant difference between treatments at each measurement point separately (1 day post inoculation (dpi), 3 dpi, 7 dpi, and 10 dpi) (p < 0.05). Different capital letters indicate difference among measurement points in each treatment separately (p < 0.05).

Figure 7

Content of (a) abscisic acid (ABA) and (b) salicylic acid (SA) in control and FHB-stressed spikes of six winter wheat varieties (Golubica, Tika Taka, El Nino, Kraljica, Galloper, and Vulkan). Bars represent mean values of four independent biological replicates ± SD. Different letters indicate significant difference among treatments in each variety separately (p < 0.05).

Figure 8

Principal component analysis (PCA) showing the relationship between reduced glutathione (GSH), oxidized glutathione (GSSG), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), content of chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (Car), chlorophyll a/b ratio (Chl a/Chl b), carotenoids/total chlorophyll ratio (Car/Chl a + Chl b), maximum quantum yield of primary photochemistry (TR₀/ABS) measured at 10 days post inoculation (dpi), performance index on absorption basis (PI_abs) measured at 10 dpi, abscisic acid (ABA), salicylic acid (SA), and type II resistance (Resistance) in the control (blue colored) and FHB-stressed (red colored) spikes of six winter wheat varieties (Golubica, Tika Taka, El Nino, Kraljica, Galloper, and Vulkan).