THE ROSETTE DISEASE OF PEANUTS (ARACHIS HYPOGAEA L.)

Abstract

Summary.Rosette is a destructive disease of peanuts in South Africa, characterised by chlorosis of the young leaves and extreme stunting. Similar conditions in this plant have been reported from tropical Africa, Java and India.Experimental evidence is advanced to show thali rosette is not carried in the seed of the peanut nor in soil which has borne a diseased crop. It was successfully transmitted to healthy plants by grafting, but not by inoculation of juice from diseased plants.Insect transmission studies demonstrated the ability of Aphis leguminosae Theo. to act as a vector of rosette. Thirteen species of leaf‐hoppers in a limited series of tests failed to transmit the disease. Aphis lguminosae was shown to obtain the virus of rosette by feeding upon a diseased plant. Winged and wingless adults, when feeding singly, were shown occasionally to transmit the disease.An infrequently occurring mosaic‐like form of the disease is considered to be due to an exceptional reaction of individual plants to infection by the same virus as that causing typical rosette.In the field this disease is believed to overwinter in diseased plants, which germinate in the late autumn and survive the drought and frost of winter. Upon these plants the aphides may spend the winter. It is thought that in the spring winged aphides become disseminated from the overwintering plants and cause localised infections in the peanut fields. Later in the season epidemic spread of rosette frequently occurs. The evidence of six years of peanut‐growing indicates that spring infection of rosette is most severe in seasons following winters of exceptional rains.Rosette disease is likely to be largely escaped in the average season if the crop be planted at the earliest favourable date. Precautions recommended for control are the destruction of surviving plants during the winter and the removal of the diseased plants which develop in the new crop. The best prospect of practical control of rosette however is thought to lie in the discovery of resistant varieties.