Phenolic Compounds in Stems of Sunflower Plants Inoculated with Sclerotinia sclerotiorum and their Inhibitory Effects on the Fungus

Abstract

Sunflower plants at I (vegetative), II (closed flower‐buds) and III (open flower‐buds) growth stages were experimentally inoculated with Sclerotinia sclerotiorum. At the 5th day after inoculation, all plants from I, III and 70 % of II (IIT) did not present wilt symptoms while 30 % of age II plants (IIs) presented severe wilt symptoms in all their leaves and had collapsed. Total soluble phenols were measured in the “lesion” (L) and its “healthy” (H) surrounding zones of all inoculated and control plants. A significant increase in phenols was found in the L and H zones of tolerant plants (I, IIt and III). The corresponding methanolic extracts showed a strong inhibitory effect on the mycelial growth (MG) of the fungus. On the other hand no statistically significant increase took place in the L zones from susceptible plants; their methanolic extracts did not inhibit MG. The chemical analysis of methanolic extracts showed that the isochlorogenic acid was the more inhibitory compound. It significantly accumulated in the L of tolerant plants but did not in those of susceptible ones.

Induction of Resistance with Benzothiadiazole in Sunflower: a Comparison of Biotrophic vs. Necrotrophic Pathosystems

“…Shetty et al (2008) also demonstrated that upon pathogenic attack peroxidases and PPO were induced together with other oxido-reductive enzymes suggesting the involvement of these enzymes in disease development and resistance. In addition, accumulation of lignin and phenolic compounds has been correlated with disease resistance in some investigated plant-pathogen interactions (Bazzalo et al, 1985;Kolattukudy et al, 1992;Chittoor et al, 1999).…”

“…In contrast, necrotrophs, like Sclerotinia sclerotiorum kill host cells at a very early stage of the infection and cause extensive tissue damage (Saharan and Mehta, 2008). Affected sunflower plants, in turn, produce phenolic compounds during pathogenesis (Hemery-Tardin et al, 1998), permitting the host to increase its resistance against the fungus (Bazzalo et al, 1985).…”

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“…Some previous biochemical studies of the Sclerotinia-sunflower interaction directed towars evaluating soluble phenolics in infected-and non-infected crop lines and wild relatives have been reported (Bazzalo et al, 1985(Bazzalo et al, , 1987Hemery-Tardin et al, 1998). These experiments have been performed under controlled conditions and were mainly focused on vegetative tissue, despite the fact of the devastating consequences of the 5 infection at the closed flower-bud developmental stage (Bazzalo et al, 1985).…”

“…Some previous biochemical studies of the Sclerotinia-sunflower interaction directed towars evaluating soluble phenolics in infected-and non-infected crop lines and wild relatives have been reported (Bazzalo et al, 1985(Bazzalo et al, , 1987Hemery-Tardin et al, 1998). These experiments have been performed under controlled conditions and were mainly focused on vegetative tissue, despite the fact of the devastating consequences of the 5 infection at the closed flower-bud developmental stage (Bazzalo et al, 1985). The accumulation of soluble phenolic compounds, their deposition on cell walls, melanization and lignification are typical sunflower responses to Sclerotinia infection which takes place in stem and leaves in both infected and healthy surrounding tissue, this pathogen-induced accumulation being, in general, lower in 10 susceptible Sclerotinia varieties (Bazzalo et al, 1985(Bazzalo et al, , 1987Hemery-Tardin et al, 1998).…”

“…These experiments have been performed under controlled conditions and were mainly focused on vegetative tissue, despite the fact of the devastating consequences of the 5 infection at the closed flower-bud developmental stage (Bazzalo et al, 1985). The accumulation of soluble phenolic compounds, their deposition on cell walls, melanization and lignification are typical sunflower responses to Sclerotinia infection which takes place in stem and leaves in both infected and healthy surrounding tissue, this pathogen-induced accumulation being, in general, lower in 10 susceptible Sclerotinia varieties (Bazzalo et al, 1985(Bazzalo et al, , 1987Hemery-Tardin et al, 1998). In a previous paper, Bazzalo et al (1991), present data of relationships between the field reactions of eight sunflower-inbred lines to the basal stalk rot and phenolic concentration in healthy tissue around the lesion zones.…”