Characterization of histological changes at the tillering stage (Z21) in resistant and susceptible wheat plants infected by Tilletia controversa Kühn

Abstract

Background: Dwarf bunt, which is caused by Tilletia controversa Kühn, is a soilborne and seedborne disease that occurs worldwide and can lead to 70% or even total losses of wheat crops. However, very little information is available about the histological changes that occur in dwarf bunt-resistant and dwarf bunt-susceptible wheat plants at the tillering stage (Z21). In this study, we used scanning electron microscopy and transmission electron microscopy to characterize the histological changes at this stage in resistant and susceptible wheat cultivars infected by T. controversa.

Results: Using scanning electron microscopy, the root, stem, and leaf structures of resistant and susceptible cultivars were examined after T. controversa infection. The root epidermal and vascular bundles were more severely damaged in the susceptible T. controversa-infected plants than in the resistant plants. The stem cell and longitudinal sections were much more extensively affected in susceptible plants than in resistant plants after pathogen infection. However, slightly deformed mesophyll cells were observed in the leaves of susceptible plants. With transmission electron microscopy, we found that the cortical bundle cells and the cell contents and nuclei in the roots were more severely affected in the susceptible plants than in the resistant plants; in the stems and leaves, the nuclei, chloroplasts, and mesophyll cells changed significantly in the susceptible plants after fungal infection. Moreover, we found that infected susceptible and resistant plants were affected much more severely at the tillering stage (Z21) than at the seedling growth stage (Z13).

Conclusion: Histological changes in the wheat roots, stems and leaves were much more severe in T. controversa-infected susceptible plants than in infected resistant plants at the tillering stage (Z21).

Keywords: Histology; Scanning electron microscopy; Tilletia controversa Kühn; Transmission electron microscopy; Wheat dwarf bunt.

Fig. 1

Histological characteristics of the roots of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under scanning electron microscopy. a Epidermal cells of the mock resistant cultivar. b Epidermal cells of the infected resistant cultivar. c Epidermal cells of the mock susceptible cultivar. d Epidermal cells of the infected susceptible cultivar. e Vascular bundle cells and cortical parenchyma cells of the mock resistant cultivar. f Vascular bundle cells and cortical parenchyma cells of the infected resistant cultivar. g Vascular bundle cells and cortical parenchyma cells of the mock susceptible cultivar. h Vascular bundle cells and cortical parenchyma cells of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47, and the susceptible cultivar was CU42. White arrows in (a-d) indicate epidermal cells, white arrows in (e-h) indicate cortical parenchyma cells, black arrows indicate vascular bundle cells, white circles in (f and h) indicate hyphae in cortical parenchyma cells, and black circles in (h) indicates hyphae in vascular bundle cells

Fig. 2

Histological characteristics of the stems of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under scanning electron microscopy. The first internodes (just above the roots) of the plants were examined. a Stem cell structure of the mock resistant cultivar. b Stem cell structure of the infected resistant cultivar. c Stem cell structure of the mock susceptible cultivar. d Stem cell structure of the infected susceptible cultivar. e Longitudinal section of the stem of the mock resistant cultivar. f Longitudinal section of the stem of the infected resistant cultivar. g Longitudinal section of the stem of the mock susceptible cultivar. h Longitudinal section of the stem of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47, and the susceptible cultivar was CU42. White arrows in (a-d) indicate stem cells, white arrows in (e-h) indicate longitudinal section stem cells, and white circles in (h) indicate hyphae in the cell

Fig. 3

Histological characteristics of the leaves of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under scanning electron microscopy. a Mesophyll cells of the mock resistant cultivar. b Mesophyll cells of the infected resistant cultivar. c Mesophyll cells of the mock susceptible cultivar. d Mesophyll cells of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47, and the susceptible cultivar was CU42. White arrows in (a-d) indicate mesophyll cells

Fig. 4

Histological characteristics of the roots of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under transmission electron microscopy. a Vascular bundle cells and cortical parenchyma cells of the mock resistant cultivar. b Vascular bundle cells and cortical parenchyma cells of the infected resistant cultivar. c Vascular bundle cells and cortical parenchyma cells of the mock susceptible cultivar. d Vascular bundle cells and cortical parenchyma cells of the infected susceptible cultivar. e Root cell contents of the mock resistant cultivar. f Root cell contents of the infected resistant cultivar. g Root cell contents of the mock susceptible cultivar. h Root cell contents of the infected susceptible cultivar. i Root nucleus of the mock resistant cultivar. j Root nucleus of the infected resistant cultivar. k Root nucleus of the mock susceptible cultivar. l Root nucleus of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47 and the susceptible cultivar was CU42. Black arrows in (a-d) indicate cortical parenchyma cells, red arrows in (a-d) indicate vascular bundle cells, black arrows in (e-h) indicate root cell contents, and black arrows in (i-l) indicate root nuclei (N: Nucleus; M: Mitochondrion; scale bar of (a-f) = 20 μm; scale bar of (g and h) =10 μm; scale bar of (i and j) =2 μm; scale bar of (k and l) =0.5 μm)

Fig. 5

Histological characteristics of the stems of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under transmission electron microscopy. a Stem cell structure of the mock resistant cultivar. b Stem cell structure of the infected resistant cultivar. c Stem cell structure of the mock susceptible cultivar. d Stem cell structure of the infected susceptible cultivar. e Stem cell nucleus of the mock resistant cultivar. f Stem cell nucleus of the infected resistant cultivar. g Stem cell nucleus of the mock susceptible cultivar. h Stem cell nucleus of the infected susceptible cultivar. i Stem chloroplast of the mock resistant cultivar. j Stem chloroplast of the infected resistant cultivar. k Stem chloroplast of the mock susceptible cultivar. l Stem chloroplast of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47, and the susceptible cultivar was CU42. Black arrows in (a-d) indicate stem cells, black arrows in (e-h) indicate stem nuclei, and black arrows in (i-l) indicate stem chloroplasts (N: Nuclei; CHl: Chloroplast; St: Starch granule; scale bar of (a-d) =10 μm; scale bar of (e-l) = 2 μm)

Fig. 6

Histological characteristics of the leaves of the mock and infected resistant and susceptible cultivars at the tillering stage (Z21) under transmission electron microscopy. a Mesophyll cell structure of the mock resistant cultivar. b Mesophyll cell structure of the infected resistant cultivar. c Mesophyll cell structure of the mock susceptible cultivar. d Mesophyll cell structure of the infected susceptible cultivar. e Nucleus of the mock resistant cultivar. f Nucleus of the infected resistant cultivar. g Nucleus of the mock susceptible cultivar. h Nucleus of the infected susceptible cultivar. i Chloroplast of the mock resistant cultivar. j Chloroplast of the infected resistant cultivar. k Chloroplast of the mock susceptible cultivar. l Chloroplast of the infected susceptible cultivar. The resistant cultivar was Mianyang 26/Yumai 47, and the susceptible cultivar was CU42. Black arrows in (a-d) indicate mesophyll cells, black arrows in (e-h) indicate leaf nuclei, and black arrows in (i-l) indicate leaf chloroplasts (N: Nucleus; CHl: Chloroplast; St: Starch granule; M: Mitochondrion; scale bar of (a-d) =20 μm; scale bar of (e-l) =1 μm)