Greatest lower bounds on the Ricci curvature of Fano manifolds

On a Fano manifold M we study the supremum of the possible t such that there is a Kahler metric omega is an element of c(1)(M) with Ricci curvature bounded below by t. This is shown to be the same as the maximum existence time of Aubin's continuity path for finding Kaler-Einstein metrics. We show that on P-2 blown up in one point this supremum is 6/7, and we give upper bounds for other manifolds.