We have assessed the constitutive total phenolic and flavonoid contents and the antioxidant activity levels in the stems and roots of nine commercial cultivars of carnation grown in Colombia showing differential response to Fusarium oxysporum f. sp. dianthi. In stems, these parameters were not correlated with resistance, but in roots, resistant cultivars exhibited higher levels of flavonoids and antioxidant activity than those found in susceptible cultivars. The activities of enzymes involved in the biosynthesis of these compounds were evaluated in the root level. Differences in the phenylalanine ammonia-lyase enzyme (PAL) activity were not correlated with resistance, but the activities of chalcone synthase (CHS) and chalcone isomerase (CHI) were higher in the roots of disease-resistant cultivars. Likewise, the transcript levels of CHS and CHI were significantly higher in resistant cultivars, as evaluated by real-time RT-PCR. These results suggested that the constitutive levels of flavonoids in the root level are most likely associated with resistance to F. oxysporum f. sp. dianthi. Such differences may be attributed to increased expression of genes in the phenylpropanoid pathway, specifically CHS and CHI, which are the enzymes that have been previously associated with the regulation of flavonoid biosynthesis in other species.
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