THE TRANSMISSION OF STREAK DISEASE BETWEEN MAIZE, SUGAR CANE AND WILD GRASSES

Abstract

General summary. This paper describes experiments in the transmission of streak disease between maize, sugar cane, D. horizontalis Willd. and E. indica Gaert. The leafhopper, Cicadulina (Balclutha) mbila Naude, acted as the transmitting agent and was usually manipulated by the single‐leaf cage method. The virus of maize streak disease is incapable of causing permanent infections of sugar cane. This conclusion is based on a considerable series of leaf‐cage experiments, in the greenhouse and in the field, and upon a large‐cage experiment. It is confirmed by certain field observations. The maize virus frequently caused transitory infections of Uba cane, in the form of a few large chlorotic streaks on the leaves. From these streaks the virus was re‐transferred to maize. All evidence indicated that the cane plant made a complete recovery from this transitory infection and ceased to harbour the virus. The virus from Uba cane readily infected Uba cane. When transferred to maize it produced in this species only a mild form of streak disease, distinguishable with certainty from normal maize streak. Repeated passage of the cane virus through maize failed to enhance its virulence to maize. Infection by the cane virus afforded no protection to a plant from infection by the maize virus; nor were hoppers similarly protected. Streak disease was discovered in the cane variety P.O.J. 213, hitherto regarded as immune. The virus from these plants produced normal streak in Uba cane and the mild form of streak in maize. After many failures the disease was transmitted experimentally to this variety from Uba cane and from P.O.J. 213 naturally infected in the field. Cuttings taken from diseased plants of P.O.J. 213 frequently produced entirely healthy plants. Lists are given of cane varieties which have been proved to be susceptible to streak disease and of those provisionally regarded as immune. A list is given of species of wild grasses believed to contract streak disease in the field. Streak in D. horizontalis has been transmitted from D. horizontals and to and from maize, but not from cane. The virus from a naturally diseased Digitaria plant, however, showed a virulence to cane greater than the maize virus. E. indica was not successfully infected from maize or Uba cane. It was once mildly infected from P.O. J. 213, and was temporarily infected from Eleusine. In experiments infective leafhoppers survived in the open through the winter at Durban and infected maize in the following spring. The infection of maize in the spring in Natal is thought to be caused usually by survival of the virus in overwintering leafhoppers and not in perennial host‐plants.