GABORONE (Reuters) - Botswana's economy will grow by an average of 4.4 percent annually from April 2017 to March 2023, the National Development Plan presented to Parliament on Wednesday showed. Botswana will introduce a new fiscal rule next year that will see its diamond producers save 40 percent of the southern African nation's annual mineral revenue in a sovereign wealth fund, according to the document. "When implemented the rule will see 40 percent of minerals revenues saved with the Bank of Botswana under the country’s sovereign wealth fund, the Pula Fund," secretary for finance and economic policy Taufila Nyamadzabo said. (Writing by Olivia Kumwenda-Mtambo; Editing by James Macharia)