Tomato bacterial wilt Ralstonia solanacearum Photo: Clemson University - USDA Cooperative Extension Slide Series, , Bugwood.org · Public domain · source ↗

Tomato bacterial wilt (Ralstonia solanacearum)

Tomato bacterial wilt is caused by the soilborne bacterium Ralstonia solanacearum (race 1, biovar III in most Indian populations) — formerly classified as Pseudomonas solanacearum. It is the single most limiting disease of tomato in continuous monoculture clusters of south India, particularly Madanapalle, Kolar (Karnataka), Hassan, Erode and Krishnagiri. Mortality on susceptible hybrids in wilt-sick fields routinely reaches 50-90% within 3-4 weeks of transplanting.

Pathogen and identification

R. solanacearum enters tomato roots through natural openings and wounds, multiplies in the xylem, and produces extracellular polysaccharides that block water transport. Field diagnosis:

Rapid wilting of the entire plant during peak afternoon heat, with leaves still green
No yellowing or leaf spotting at the early stage — distinguishes bacterial wilt from fusarium wilt
Brown vascular discoloration when the stem is cut longitudinally; squeeze the cut stem and watch for white milky bacterial ooze drip from the cut surface within 1-3 minutes (the "ooze test") — a definitive diagnosis
Adventitious roots sometimes form on the lower stem in slower infections
Patchy mortality spreading along drainage lines and waterlogged spots

The ooze test, conducted by placing a 3 cm cut stem section in a glass of clear water, is the standard farmer-level diagnosis.

Hosts and lifecycle

R. solanacearum has a very wide host range — tomato, brinjal, chilli, potato, ginger, banana, capsicum, tobacco, geranium and several solanaceous weeds (Solanum nigrum, Datura). The bacterium survives in soil for 2-7 years on infected debris and host roots, in irrigation water, and in latently-infected weed hosts. Optimum infection occurs at 28-35 deg C with high soil moisture; this matches the summer transplant window in south Indian tomato clusters. Spread is via infested soil clinging to seedlings or implements, surface irrigation water, root-knot nematode injury (Meloidogyne incognita), and contaminated transplants.

Damage and economic impact

In endemic clusters, wilt-sick fields force farmers to either abandon the field for tomato (and shift to non-host crops like maize, sweet corn, marigold) or invest in grafted seedlings on wilt-resistant rootstocks. Loss on susceptible cultivars reaches 50-90% plant mortality plus complete fruit-yield loss on remaining plants. The economic impact has visibly reshaped cropping patterns across the Kolar-Madanapalle and Krishnagiri belts.

Management

A truly integrated package is required — single-tactic control is rarely effective:

Resistant rootstocks via grafting (the most successful tactic in commercial clusters): wedge-graft tomato scion on Hawaii 7996, Hawaii 7997, Mahyco RTW, BWR-1, BWR-5 rootstocks; commercial nurseries in Madanapalle, Hosur and Mulbagal now supply grafted seedlings at Rs 6-10 per plant. Survival in wilt-sick fields rises from 10-30% to 80-95%
Resistant varieties: Arka Abha, Arka Alok, Arka Rakshak, Sakshi (IIHR), Mukti (IIVR); lower mortality but yield lower than commercial F1 hybrids — used in subsistence farming
Cultural / agronomic: 3-4 year rotation with non-solanaceous crops (marigold, paddy, maize, sweet corn, finger millet); deep summer ploughing; raised-bed transplant with drip irrigation; nematode control through marigold trap-cropping or fluensulfone soil application
Soil amendment: organic FYM 25 t/ha + bleaching powder 30 kg/ha + neem cake 250 kg/ha at land preparation; Pseudomonas fluorescens talc formulation 10 g/L drench at transplant
Drainage: avoid low-lying or waterlogged plots; use double-row raised beds with drip
Sanitation: do not transport soil from wilt-sick field to clean field on implements or feet; use only certified, wilt-tested commercial seedlings

Sources

Bacterial wilt of tomato. ICAR-Indian Institute of Horticultural Research, Bengaluru.
Ralstonia solanacearum factsheet. CABI Plantwise.
Grafting for bacterial wilt management in tomato. ICAR-Indian Institute of Vegetable Research, Varanasi.