Milk Thistle,Silybum marianum(L.) Gaertn., Flower Head Development and Associated Marker Compound Profile

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Abstract
Flower head development and marker compound changes were examined for milk thistle grown under dryland conditions during the 1998 and 1999 growing seasons. Flower heads harvested at the early flowering, mid-flowering, late flowering, and dehiscing (seed development) growth stages had average seed/ovule weights of 5 mg, 13 mg, 21 mg, and 26 mg, respectively. At the time of harvest, the plants contained flower heads at all stages of development. During the 1999 harvest, the average plant produced 2.0 g, 2.9 g, and 3.4 g of dry seeds per flower head, corresponding to mid-flowering, late flowering, and dehiscing development stages of the flower. The silymarin and fixed-oil content for the 1999 seeds were 1 mg, 14 mg, and 24 mg of silymarin and 15 mg, 168 mg, and 252 mg of lipid/g dry weight for mid-flowering, late flowering, and dehiscing development stages, respectively. The highest silymarin yield was obtained from late flowering and dehiscing flower heads in early September of both test years.