Flat top decay syndrome of the giant cardon cactus (Pachycereus pringlei): description and distribution in Baja California Sur, Mexico

Abstract

The giant columnar cardon cactus (Pachycereus pringlei) appears to have an ailment(s) that is destroying a large number of plants. The causal agent(s), whether biotic or abiotic, has yet to be determined. Two forms of symptom development have been recorded. The first is a circular tissue decay on a branch leading to death of the growing tip. In this case, the dead portion detaches and forms a "flat top" on the living part (hence the proposed name for this phenomenon). Progressive degeneration and death of the plant ensue. The second form is an initial circular crack on the branch without decay. Later, the green branch above the crack detaches, creating the characteristic flat top. A third type of degeneration was also observed: fatal bleaching. The time period between symptoms is unknown. It primarily affects mature, more than 100-year-old plants, but relatively young plants are also affected. Thirty-one field surveys covering the entire state of Baja California Sur found four major and three smaller centers of flat top decay. We believe that flat top decay syndrome of the cardon cacti in Baja California is common and widespread. Key words: cactus decay, cactus deformation, cactus diseases, columnar cacti, Pachycereus, phytopathology.