Central Role of Salicylic Acid in Resistance of Wheat Against <Emphasis Type="Italic">Fusarium graminearum</Emphasis>

Head blight caused by Fusarium graminearum (F. graminearum) is one of the major threats to wheat and barley around the world. The importance of this disease is due to a reduction in both grain yield and quality in infected plants. Currently, there is limited knowledge about the physiological mechanisms involved in plant resistance against this pathogen. To reveal the physiological mechanisms underlying the resistance to F. graminearum, spikes of resistant (Sumai3) and susceptible (Falat) wheat cultivars were analyzed 4 days after inoculation, as the first symptoms of pathogen infection appeared. F. graminearum inoculation resulted in a greater induction level and activity of salicylic acid (SA), callose, phenolic compounds, peroxidase, phenylalanine ammonia lyase (PAL), and polyphenol oxidase in resistant versus susceptible cultivars. Soil drench application to spikes of SA, 24 h before inoculation with F. graminearum alleviated Fusarium head blight symptoms in both resistant and susceptible cultivars. SA treated plants showed a significant increment in hydrogen peroxide (H₂O₂) production, lipid peroxidation, SA, and callose content. SA-induced H₂O₂ level seems to be related to increased superoxide dismutase and decreased catalase activities. In addition, real-time quantitative PCR analysis showed that SA pretreatment induced expression of PAL genes in both infected and non-infected head tissues of the susceptible and resistant cultivars. Our data showed that soil drench application of SA activates antioxidant defense responses and may subsequently induce systemic acquired resistance, which may contribute to the resistance against F. graminearum. These results provide novel insights about the physiological and molecular role of SA in plant resistance against hemi-biotrophic pathogen infection.     

The effect of methyl jasmonate on enzyme activities in wheat genotypes infected by the crown and root rot pathogen <Emphasis Type="Italic">Fusarium culmorum</Emphasis>

The hemibiotrophic pathogen Fusarium culmorum (Fc) causes crown and root rot (CRR) in wheat. In this study, MeJA treatment was done 6 h after pathogen inoculation (hai) to focus the physiological and biochemical responses in root tissue of the susceptible wheat cv Falat, partially resistant cv Pishtaz and the tolerant cv Sumai3 at the beginning of the necrotrophic stage. The results indicate that treatment with MeJA at 6 hai significantly delayed the necrotic progress in cv Falat, whereas no significant difference was seen in other cultivars. The activities of pathogen responsive defense-related enzymes (SOD, CAT, POX, PPO, LOX and PAL), total phenols and callose contents were higher in Sumai3, while treatment with MeJA significantly increased these enzymes activities and total phenols content in Falat, signifying the most sensitive cultivar which had a weak reaction to the pathogen but a strong response to MeJA treatment. Additionally, MeJA treatment decreased the level of H₂O₂ and MDA contents particularly in cv Falat. This is the first work reporting the regulation of defense-related enzymes by MeJA treatment at particular time point of 6 hai suggests the possible role of JA in regulating basal resistance in CRR pathogen–wheat interaction. Taken together, our data add new insights into the mechanism of wheat defense including enzymatic events controlling wheat protection against Fc infection.     

Changes in Anatomical Features and Protein Pattern of Sunflower Partially Resistant and Susceptible Lines During Infection By Virulence Factors of Sclerotinia Sclerotiorum

Helianthus annuus L. as an oil seed crop is widely grown throughout the world. One of the most destructive diseases of sunflower is stem rot caused by Sclerotinia sclerotiorum. Oxalic acid is the major virulence factor of this necrotrophic pathogen. It is important to further investigate plant responses to this non-specific toxin. Therefore, in the present study, we compared the patterns of total soluble proteins and xylem morphology of partially resistant and susceptible sunflower lines after treatment with Sclerotinia culture filtrate. The basal stems of both lines were treated with 40 mM oxalic acid (pH 3.7) of fungus culture filtrate and samples were collected at 24, 48 and 72 hours post treatment. In SDS-PAGE protein pattern new protein bands appeared in both lines after treatment. These observations suggest induction of stress-related proteins upon culture filtrate treatment. The identities of these new proteins need to be more clarify in future investigations. The changes in xylem morphology and degree of lignification of both lines was studied by light microscopy and microtome sectioning techniques after treatment with S. sclerotiorum culture filtrate. Anatomical investigations revealed changes in xylem diameter and xylem lignification of treated lines at various time points. More lignin deposition in xylem vessels of partially resistant line has been observed after treatment. In addition, the size of xylem vessels in partially resistant line has been sharply decreased upon pathogen filtrate treatment. The results of this study will help us gain a more complete understanding of resistance mechanisms to this cosmopolitan and devastating pathogen.     

Exogenous Methyl Jasmonate Treatment Induces Defense Response Against Fusarium culmorum in Wheat Seedlings

Journal of Plant Growth Regulation - The Fusarium crown and root rot (FCRR) pathogen Fusarium culmorum (Fc) is a hemibiotrophic pathogen, with a short biotrophic phase preceding necrotropism....