Witches'-Broom of Mamane

Mamane (Sophora chrysophylla: Fabaceae) is a small to medium sized tree endemic to Hawai‘i and an important component of mid to upper elevation forests.   Mamane forms a dominant element of subalpine vegetation in dry to mesic shrub and forest land on most of the major islands and provides critical habitat for the endemic palila (Loxioides bailleui), an endangered bird of the honeycreeper group.

A disease of mamane has become apparent in recent years.  The most prominent symptom of the disease is the formation of witches'-brooms comprised of abnormally thickened, roughened, upright twigs with shortened internodes and unsuppressed lateral buds.  The brooms arise from contorted, spindle-shaped, or sometimes gall-like stem thickenings.  Numerous black, well-developed stromata are evident erupting through split bark of dead brooms and swollen areas of branches.  Individual diseased trees may have only one or a few infection sites, or the entire tree may be covered with witches'-brooms.  Infected tissue dies, thus, in the case of entire trees, infection may lead to the death of the tree itself.  At present, I consider the disease to have been long present in mamane stands and to have escaped previous observation, rather than resulting from a recent introduction of the pathogen.

I described the causative fungus, Botryosphaeria mamane, as a new species based on the unusually large spores, particularly the macroconidia, and on its occurrence on an endemic Hawaiian host with no apparent affinity to a similar introduced species (Gardner, 1997).  Botryosphaeria is a well known genus containing pathogens of woody plants elsewhere, but it is usually associated with bark cankers and branch and twig dieback.  Its association with abnormal development of shoots to form witches' brooms, such as occurs on mamane, is unusual and further distinguishes B. mamane as a distinct species.

    Left: diseased, broomed branch; Right: normal healthy branch.

   Broomed branches of a dead tree.

   Branches of a young, previously vigorous tree that had become heavily infected.

   Young brooms are occassionally pendulous, hanging from a branch with broom branches recurving to attain upright growth.

   A mamane tree with old witches' brooms.

    Prominent stromata, some exuding spore tendrils of macroconidia, on dead broom tissue.

    A cross section through a typical multilocular stroma (left), possibly containing macroconidiomata, microconidiomata, and ascomata.   Closeup of an ascoma with a well-developed ostiolar neck (right).

     Young asci of Botryosphaeria mamane (right); ascospores (left).

   Macroconidia of B. mamane.