UPDATE 1-Mannatech founder resigns as chief executive

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Aug 21 (Reuters) - Mannatech Inc (MTEX.O) said its founder Samuel Caster resigned as chief executive officer effective immediately and Terry Persinger has been appointed interim CEO.

Caster, who founded the company in 1993, will serve as non-executive chairman of the board, Mannatech said.

In July, the Attorney General of Texas had charged the provider of nutritional supplements and Caster with operating an illegal marketing scheme.

Persinger, who joined Mannatech in 1999, was serving as president and chief operating officer of the company.

Persinger plans to retire from Mannatech in June 2008, as planned earlier, the company said in a statement.

The company said it promoted Executive Vice President of global operations Terence O'Day to COO position. (Reporting by Ramya Dilip in Bangalore)