May 2004. Green leaves of yam are falling on the soil while the plant is not yet mature. The photo was taken at Centre des Tubercules Tropicaux, New Caledonia. There is necrosis at the base of the petiole. The symptom was noticed 2 weeks’ ago on one variety. Today, the leaf drop has stopped and the plant is alive. The last time the symptom was seen was in 1989, in the yam collection. But at that time almost all leaves of most varieties had fallen and yields were very low.

There are possibily two cases: 1) anthracnose. On some varieties the fungus attacks the petioles, whereas most other parts of the foliage are free from infection. This does not look to be the cause in this case as there is no sign of the disease; 2) by Rhizoctonia attack on the roots. Look for brown/orange lesions on the main roots and isolate from these and other parts of the root system.