- Brown rot of potatoes is caused by Pseudomonas solanacearum, a non-spore forming, non-capsulate, Gram negative, aerobic bacterium.
- Strains vary in the adaptability to the environment and to host species.
- Environmental requirements
- Temperature: optimum 30 to 37 oC, declining at 43 oC, uncommon below 15 oC. Race 3 (race infecting potato), optimum 27 to 28 oC.
- Moisture: survival and infection favoured by high soil moisture, easily desiccated.
- Members of the Solanaceae including potatoes, tomatoes, tobacco, solanaceous weeds e.g. nightshade.
- Also a wide range of other crops.
- Wilting of foliage, leaves become chlorotic and die.
- Vascular bundles in the stem become infected with bacterial slime, visible as dark streaks on the stem; cut surfaces ooze slime.
- Tubers develop a brown coloration on the vascular ring, which exudes bacterial slime if compressed.
- Apical eyes of the tuber exude slime, to which soil particles adhere.
- Modes of dispersal and sources of inoculum
- Inoculum is mainly soil borne, infection is generally introduced through seed tubers and remains in the soil, associated with plant debris and solanaceous weeds.
- Persistence may be for up to two years although little is known of persistence in cool, temperate conditions.
- Use disease free seed.
- Rotation: persistence measured as 2-3 years but circumstantial evidence for 7+ years.
- Genetic resistance: related to resistance to infection and heat tolerance of the cultivar.
- Soil type: chalky soils may suppress P. solanacearum.
- Soil amendment: possible effects of calcium and sulphur; interaction of other nutrient deficiencies with cultivar resistance.
- Control of nematode populations: synergistic interaction with root knot nematode.
- Chemical control: soil fumigants, some effects of MBC, dinitroaniline herbicides (historical).
- Biological vaccination: pre-treatment with avirulent strains of P. solanacearum (experimental)
Brown rot notes
Brown rot 1996 (Symptoms; biology; control)