Looks like stem canker.

What are your growing conditions like? High humidity? Desert?

Here is a link that might be useful: canker page at sactorose

hi hoovb.
thanks for the reply! it looks like the canker!
and what confuse me is that the canker almost happened in the trunk of the rootstock, where there were bud eye.
if the canker tends to attack the site of the de-eyed, dose that mean tree rose is not suitable for our condition?
actually i found a suckers died a couple days ago, the lower part of the stem turned black.
the climate here during springtime is very damp, it rains a lot, the lowest temprature is about -3â to -1âÂÂ.

Rose standards (or rose trees) are almost always double crafts. The flowering portion is crafted onto the central cane (trunk), which is crafted onto a rootstock -- so the rose standard is actually 3 different rose varieties growing symbiotically as one plant.

The trunk portion of a rose standard is extremely vulnerable, primarily because of its total exposure to the elements. To me, the damage on your plant appears to be sun scald . Persistant dry, desiccating winds and/or winter conditions can produce similar damage.

Generally speaking, most gardeners take certain precautions to protect the trunk of a rose standard (especially newly planted ones). It's always advisable to support the trunk with a stake that is somewhat wider than the trunk itself. (The taller the standard, the more important it is to provide support.) The stake should be placed so that it shades the trunk during hours when sun exposure is most intense. Where winters are severe, standards are sometimes surrounded by mesh cages which are filled with dried leaves or some form of loose mulch.

Rose standards are labor-intensive additions to a garden -- especially during the several seasons it usually takes for the trunks to develop girth and rigidity. If well grown they're worth the effort, though.