* Major shareholder advisers have given thumbs down (Adds details on vote, update on other key shareholders): LONDON/FRANKFURT (Reuters) - Bayer’s largest shareholder, fund manager BlackRock, will not support the German company’s management in a key vote at its annual general meeting (AGM) on Friday, two people familiar with the situation told Reuters. About 30 billion euros ($34 billion) has been wiped off the pesticides and drugs firm’s market value since August, when a U.S. jury found Bayer liable because Monsanto, which it bought for $63 billion last year, had not warned of alleged cancer risks linked to its weedkiller Roundup.