Diseases

Bacterial wilt and brown rot (Ralstonia solanacearum)

Bacterial wilt is the main bacterial constraint on potato in warm highlands from East Africa to South-East Asia, and the same organism is regulated as brown rot in Europe and North America. It spreads in seed, soil and water, and no chemical controls it.

Last updated: 7 November 2026

At a glance
Cause	Ralstonia solanacearum species complex (EPPO: RALSSO)
Key strain on potato	Race 3 biovar 2 (phylotype II)
Chemical control	None effective
Seed tolerance	Zero in all certified classes

Cause

The Ralstonia solanacearum species complex comprises R. solanacearum in the strict sense, R. pseudosolanacearum and R. syzygii (EPPO Global Database). On potato in the tropical highlands, race 3 biovar 2 is the main strain, for example in Indonesia, and strains of phylotype II sequevar 1 spread through latently infected seed in Uganda.

Symptoms

Leaves wilt in warm weather while the plant stays green, often starting with one stem.
Cut stems and tubers show browning of the vascular ring and a grey-white bacterial ooze, which may also appear at the eyes and the stolon end, sticking soil to the tuber surface.

How it spreads

Latently infected seed tubers are the main route, which is why the disease crosses district and national boundaries in seed.

The bacteria also persist in soil and plant debris and move in contaminated irrigation water, on machinery and on tools.

Where the risk is highest

Warm and tropical highlands: Indonesia, where it is endemic and causes losses of 15 to 25 percent; the Philippines; the East African highlands, where surveys in Uganda had 47.5 percent of respondents in Kabale and 36 percent in Kisoro naming it a major constraint; Ethiopia; Kenya; and Brazil. In Europe and North America it is regulated, with occasional outbreaks.

In Ethiopia, bacterial wilt has been found at high frequency in the seed potato system, and the authors of a 2025 study of seed quality assurance warn that exports to countries where it has not been reported are at risk (Tessema et al., Agriculture, 2025).

Management: cultural

Plant clean, tested seed. This is the single most effective step.
Rotate with non-host crops for several seasons and control volunteer potatoes and solanaceous weeds.
Do not irrigate from surface water that may be contaminated, and clean tools and machinery between fields.

Management: resistant varieties

Varieties with partial tolerance exist. Igorota, a CIP-derived variety released in the Philippines in the late 1990s, was bred for tolerance to bacterial wilt and late blight, with an estimated 10 to 15 percent of planted area (BPI Philippines variety registry, as summarised in the corpus).

Management: chemical and regulatory notes

No effective chemical control is available. Regulatory notes: in the EU the organism is regulated as a quarantine pest under plant-health law, and seed lots are tested by PCR, with a 0 percent tolerance in every certified class (EU Directive 2002/56/EC framework).

Seed certification

Zero tolerance for brown rot applies in every certified class, and laboratories test seed lots by PCR. Pre-basic material comes from tissue culture, which cleans the line.

In Ethiopia, about 98.3 percent of potato planting stock may come from the informal system, and under the quality declared seed approach 90 percent of field quality control is internal and 10 percent external, based on visual observation. The 2025 study calls this 'a recipe for the transfer of seed-borne disease, particularly bacterial wilt' (Tessema et al., 2025).

Seed certification schemes set maximum tolerances for disease by class, from Pre-Basic to Certified, and regulated bacteria such as ring rot and brown rot are held at zero in every class (EU Directive 2002/56/EC framework; Scottish SPCS and Dutch NAK schemes as summarised in the Potatopedia corpus).