Uniform bundles on generalised Grassmannians

Let $E$ be a uniform bundle on an arbitrary generalised Grassmannian $X$ defined over $\mathbb{C}$. We show that if the rank of $E$ is at most $e\mathrm{.}d\mathrm{.}(\mathrm{V}\mathrm{M}\mathrm{R}\mathrm{T})$, then $E$ necessarily splits. For some generalised Grassmannians, we prove that the upper bounds $e\mathrm{.}d\mathrm{.}(\mathrm{V}\mathrm{M}\mathrm{R}\mathrm{T})$ are optimal and classify all unsplit uniform bundles of minimal ranks. Under some special assumptions, we show that morphisms to some generalised flag varieties must be constant, which partially answered a conjecture of Kumar.