Wellman's Leaf and Fruit Spot of Arabica Coffee in New Guinea.

Abstract

A leaf and fruit spot of Arabica coffee, variety ' Bourbon', in New Guinea is similar to Wellman's blister spot of coffee in Costa Rica, attributed to a virus, and to Bitancourt's oily spot in Brazil. The leaf symptoms appear distinct from those of ring spot of coffee in the Philippines. In experiments, spots occurred on leaves produced on tips of affected bushes kept under protective insecticide cover, indicating the probable systemic nature of the condition. Spots occurred on the cotyledons of volunteer seedlings in the field at 5,000 ft. altitude but not on the subsequent leaves of such seedlings transplanted to the glasshouse at sea level. In other experiments at sea level, spots were only rarely observed on new leaves grown after transplanting of older affected seedlings and a mature bush or on the new leaves of cuttings taken from affected plants. Nor were spots seen on leaves grown on bealiby scions grafted onto affected bushes in the Highlands, except for four spots on three leaves of two grafts. The condition was not transmitted through 477 seeds from affected bushes, the seedlings having been kept under observation for from 18 to 24 months. In five areas totalling 629 trees with five per cent. of trees initially affected, only two additional trees (0.3 per cent. of the total) were observed to become newly infected during observation for one year. No particles which could be ascribed to a virus were observed in preparations of sap extracts examined in the electron microscope. As at least three common names are being used for conditions with similar symptoms in America, in New Guinea the condition is being designated as Wellman's leaf and fruit shot.