Abstract
A description is provided for Streptomyces ipomoeae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Ipomoea batatas. DISEASE: Soil rot, pox, pit, or ground rot of sweet potato. All underground parts of the plant can be attacked. Dark brown to black spots of varying shapes and sizes are formed on roots, tubers and underground parts of stems. In serious attacks many of the fine feeding roots are either destroyed or more or less malformed. The above-ground parts of the plants then show poor growth and thin, pale green leaves. Yields are drastically reduced on such plants. In the early stages lesions on the root-tubers are covered by the epidermis, but this cracks and breaks up, leaving a hole or pit. These pits can be quite large and may girdle the potato, preventing growth at that point. Continued growth on either side results in a dumbell-shaped, or other misshapen potato. GEOGRAPHICAL DISTRIBUTION: USA, occurring more or less locally in most, if not all, of the States where sweet potatoes are grown. (CMI Map 301, ed. 2, 1975). TRANSMISSION: The disease is soilborne and most infection is thought to take place when plants are set out into already infested fields, but infection can occur in the nursery bed. The pathogen can be spread to new areas in a variety of ways. Infected planting material is probably the most frequent, but contaminated agricultural tools, workers' boots, feet of grazing animals, and even the wheels of vehicles may also play a part. Once established in a field, the organism can continue to live in the soil until the host is present and conditions are right for infection.
Ethylene is involved in the nodulation phenotype of Pisum sativum R50 ( sym 16 ), a pleiotropic mutant that nodulates poorly and has pale green leaves
