Witches' broom disease investigations, 6: The infection of flower cushions and pods of cacao by Marasmius perniciosus Stahel

1. The work of Stahel in Suriname on the pod- and cushion-infecting stages of witches' broom disease has been confirmed and amplified under Trinidad conditions. 2. Climatic factors are of considerable importance, as infections only occur during the wet season, but there may be a lag of up to four months between infection and the appearance of visible symptoms on the pods. Cushions usually show symptoms three to five weeks after inoculation but may become dormant and produce neither diseased flowers nor shoots until the next flower flush. 3. All types of diseased cushion, including those with parthenocarpic pods, were produced by artificial inoculation. 4. Diseased pods were classified as swollen pods, indurated pods and indirectly infected pods, following the system devised by Stahel. Swollen and indurated pods were readily produced by artificial inoculation; but the development of the indirectly infected or "parthenocarpic" pods has not been satisfactorily elucidated. 5. Cherelles infected when less than 3 cms. in length usually develop into swollen or distorted pods, while larger cherelles become indurated but not distorted. According to Stahel, pods can be infected when more than half-grown, but only develop lesions in the shell. The existence of this type of infection in Trinidad is suspected but has not so far been demonstrated by artificial inoculation. 6. Attempts to improve the inoculation technique, and thus to make results more certain during the wet season, and perhaps, possible even in the dry season, have so far proved unsuccessful.