Corynebacterium betae. [Descriptions of Fungi and Bacteria].

A description is provided for Corynebacterium betae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Beta vulgaris, both red beet and mangold. Rarely seen on sugar beet. DISEASE: Silvering disease of red beet. Systemic symptoms are first seen on a small percentage of plants 6-8 weeks old. One or more leaves show silvering along the veins. The whole leaf becomes affected and cracks may appar in places in the upper epidermis; these expose parts of the tissue beneath and give a roughened appearance to the leaf. Symptoms spread to other leaves and the plant wilts and dies, sometimes in only a few days, sometimes in several weeks. Lesions may develop on the leaves of healthy plants nearby. These may be either silvery spots 1-5 mm diam., with centres often showing cracks, or a silvery and perhaps cracked band at the edge of the leaf. The spores do not appear to spread, but the marginal silvering extends along the veins and becomes systemic, involving the whole leaf and, eventually, to the whole plant. Plants in flower may show silvering of bracts and seed clusters. Petioles, stems and roots show no consistent internal symptoms. GEOGRAPHICAL DISTRIBUTION: United Kingdom, Republic of Ireland. TRANSMISSION: In the seed of infected plants. About 1-2% of the young plants (stecklings) arising from such seed show infection a few weeks after sowing. Transmission from plant to plant occurs both within the seedbed and to neighbouring seedbeds up to at least 50 yards downwind. This seems to be mainly in wind blown droplets in the autumn and may be serious if the autumn is wet. Also readily transmitted on knives used to trim the roots of stecklings before planting out. Various insects, larvae and slugs failed to transmit the disease in experiments (Keyworth & Howell, 1961).