BERLIN, Sept 25 - Germany's Ifo business climate index rose for a fifth month in a row in September, as optimism about the future outweighed a gloomier assessment of the current situation, the Ifo economic institute said on Thursday. Ifo said the west German business climate rose to 91.9 from 90.8 in August, in line with a median forecast in a poll for a rise to 92.0 . But the Munich-based think tank, which each month polls 7,000 firms, said the move was limited to expectations for the next six months. Firms' assessment of their current conditions deteriorated. The east Germany business climate index dipped slightly to 104.0 from 104.1, also due to a gloomier assessment of current conditions. The rise in the Ifo came after Belgium and Italy reported declines in their main business confidence indicators.//