Complex sentence: Phytoplasmas are able to move within the phloem from source to sink and they are able to pass through sieve tube elements, but spread more slowly than solutes, for this and other reasons movement by passive translocation is not supported.
Split into simpler sentences: Phytoplasmas are able to move within the phloem from source to sink, and they are able to pass through sieve tube elements. But since they spread more slowly than solutes, for this and other reasons movement by passive translocation is not supported.