Study of the expression of shikimate dehydrogenase activity in sunflower genotypes treated with Sclerotinia sclerotiorum

The expression of shikimate dehydrogenase in cotyledons of five sunflower inbred lines treated with Sclerotinia sclerotiorum was compared with exogenous application of synthetic oxalic acid. Normally, shikimate dehydrogenase becomes enzymatically active in sunflower at seed germination stage, and it reaches its maximum during the cotyledon stage, gradually decreases and disappears after four leaf stage. We found that shikimate dehydrogenase activity was very faint in control plant protein extract whereas its intensity greatly increased in samples derived from seedlings inoculated with S. sclerotiorum as well as with synthetic OXA at the same stage. The expression of shikimate dehydrogenase at the first phase of growth may serve as a tool for rapid screening and selection of resistant genotypes of sunflower to S. sclerotiorum. Some agronomy parameters in terms of plant dry and fresh weight and the total chlorophyll concentration were assessed for both treatments compared with their untreated controls. Exogenous oxalic acid treatment caused more deleterious effects in comparison with its endogenous production of the pathogen, considering stem rot and eliciting photosynthesis reduction. The excessive toxicity of exogenous treatment suggests that S. sclerotiorum infection triggers a more complex metabolic pathway involvings oxalic acid secreted by the pathogen.

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