Bacterial top rot: a new disease of the potato

Summary ‘Top rot’, a new bacterial disease of potato was found to occur in India. Water-soaked lesions developed on succulent stems, petioles and leaves. On stems and petioles the lesions enlarged into stripes turning black, which ultimately enveloped the affected portion and caused a soft rot, resulting in toppling of the stem/leaf. The affected tissues were covered with whitish bacterial exudates under high humidity but became dried and shrivelled under dry conditions. Leaflet infection occurred through infected petioles, via mid-rib and veins, or through the margins, resulting in rotting and blighting. The bacterium also caused soft rot of tubers. The disease was favoured by high humidity and a temperature range of 25–30°C. The causal bacterium was identified asErwinia carotovora var.carotovora.