The question is, did it die because of the stems turning black, or did the stems turn black because it died of a root infection that cut circulation off to the stems? You can see by the wrinkled texture of the still-green portion of the canes that no circulation is getting up to the canes from the roots. They are shriveled.

Look at the roots, are they rotted, soft, gooey? Did the soil smell sour and foetid when you pulled the rose out of the ground? Is the area constantly soggy? Those conditions would point to rot.

Is it possible a large pet dog urinated several times on the rose and gave it such a blast of ammonia that the rose was poisoned? Did it accidentally get too much fertilizer? That would point to death by chemical damage.

A bacterial infection would be another possible culprit--are there other problem plants in your yard?