TRANSMISSION OF GROUNDNUT ROSETTE VIRUS

Abstract

The rosette virus was transmitted to groundnut plants, if previously etiolated, bymechanical inoculation of juice with ‘Celite’ addition; but only a small proportion of the inoculations succeeded.Aphis craccivora (Koch), the known vector, transmitted the virus by feeding on germinating groundnut seeds; and from this fact we developed an experimental technique that is convenient and flexible.Different races of this species appeared to vary in inherent efficiency in transmission, and one failed ever to transmit. Within races that could transmit, all larval forms and alate and apterous adults might transmit; but alatae were sometimes significantly more efficient than apterae, and at other times the converse held. A field experiment showed that wingless forms, moving over the soil surface, might play a predominant part in secondary spread around a rosetted plant.Comparative tests with groups of I, 2, 3 and 4 infective aphids supported the hypothesis that infections by this vector are individual and independent.Single aphids, tested for 24 hr. on 10 successive days without access to an outside source of virus, might infect on any day up to the tenth. Similar results were obtained in a succession of I hr. tests on a single day. In the infected seed the virus rapidly became available to feeding aphids; previously non‐infective aphids acquired the virus by feeding on a seed during the third day from the first exposure of this seed to infective aphids.