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Can grafting protect tomatoes from bacterial wilt?
In a Paraguayan greenhouse where bacterial wilt had been seen every season for five years, tomatoes grafted onto a wilt-resistant rootstock showed no wilt at all, while 86.7 to 100% of ungrafted plants wilted. The grafted plants also gave more fruit.
One greenhouse at the National University of Asunción in Paraguay had grown tomatoes for about 15 years in a row, and bacterial wilt (caused by the soil bacterium Ralstonia solanacearum) had been seen there continuously for the past five. The team wanted to know whether grafting two widely grown tomato cultivars onto a resistant rootstock would keep them productive in that soil (Godoy Medina et al., 2026).
What this means for your grow
If tomatoes keep wilting in the same greenhouse soil year after year, grafting onto a resistant rootstock is worth knowing about. In this trial, not one grafted plant showed wilt symptoms, and grafted plants gave more marketable fruit per plant. It was one rootstock, two cultivars, one greenhouse and one season, and the authors did not weigh the extra cost of grafted seedlings, so treat it as a promising option rather than a sure fix.
What did the team do?
Two commercial hybrid tomatoes, Ravena and Grazianni, were each grown two ways: on their own roots, or grafted onto Woodstock, a rootstock its maker (Sakata Seed Corporation) describes as highly resistant to Ralstonia solanacearum. The seedlings were joined with a splice graft, a 45° bevel cut on both stems held together with a small plastic clip, then healed for seven days in a dark chamber at 22 °C and 80% relative humidity.
The plants went into soil beds under black plastic mulch with drip irrigation, were trained to a single stem and fertigated weekly. Nobody added the bacterium: the team relied on the infection already in the greenhouse soil, checked every plant daily for wilting, and cultured bacteria from wilted stems to identify the cause. Fruit was picked 12 times between September and mid-November 2022.
What did they find?
- No wilt on grafted plants. None of the 60 grafted plants of either cultivar showed wilt symptoms. Among ungrafted plants, 60 of 60 Ravena (100%) and 52 of 60 Grazianni (86.7%) wilted.
- More fruit. Grafted plants carried 29.62 fruits per plant, against 24.94 on ungrafted plants, an 18.8% increase.
- Heavier fruit. Average fruit weight was 104.10 g on grafted plants and 94.80 g on ungrafted ones. Grafted fruit were longer (6.73 cm against 6.21 cm), but not significantly wider.
- More to sell. Marketable fruit came to 1937.19 g per plant on grafted plants and 1454.53 g on ungrafted plants. Total fruit was 3078.61 g against 2373.20 g.
- The share of sellable fruit depended on the cultivar. Grafting raised the marketable share in Grazianni (62.3% against 57.7%) but lowered it slightly in Ravena (63.1% against 66.4%).
- Lab checks pointed to the expected culprit. Bacteria from wilted plants grew and stained the way Ralstonia solanacearum does, and gave the DNA band expected for it.
What could it mean?
The authors conclude that grafting onto Woodstock significantly increased fruit number, fruit mass and marketable yield in both cultivars under subtropical protected cultivation, and suppressed bacterial wilt symptoms under natural soil inoculum pressure. They call it a combined strategy for yield and disease management where soil-borne Ralstonia solanacearum is a limiting factor. They are careful to add that this is not proof of genetic resistance or of how the protection works, and they propose controlled inoculation trials to confirm it. For now the result speaks most to tomato growers under cover in subtropical regions where this soil-borne wilt limits production, and the authors note that the cost of grafted seedlings still needs weighing before growers adopt it.
What were the limitations?
- Only one rootstock and two cultivars were tested, at a single site in a single season.
- The amount of the bacterium in the soil, and how it was spread through the greenhouse, was not measured, so each plot's disease pressure is unknown.
- Wilt counts were pooled per treatment, so incidence could not be analysed statistically plot by plot.
- The DNA test had no positive or negative control lanes and the products were not sequenced, so the authors treat it as supporting evidence rather than independent confirmation.
- No cost-benefit analysis of grafted seedlings was done, and no physiological or root measurements were taken.
Trial details
- Where: Horticultural Center of the Facultad de Ciencias Agrarias, Universidad Nacional de Asunción (FCA-UNA), San Lorenzo, Central Department, Paraguay (25°33’ S, 57°52’ W). A pampean-type greenhouse, 25 m long and 6 m wide, used for tomatoes for about 15 consecutive years, with bacterial wilt observed continuously over the past five years.
- When: April to November 2022. Rootstock sown 12 April, scions sown 19 April, grafted 19 May, transplanted 3 June; 12 harvests from September to mid-November.
- Crop: tomato (Solanum lycopersicum) hybrids Ravena and Grazianni, ungrafted or grafted onto Woodstock rootstock (Sakata Seed Corporation). Graft take at transplanting was 92% for Grazianni and 90% for Ravena.
- Grafting: splice graft with a 45° bevel cut about 5 cm above the base, joined with 2 mm plastic clips; seven days in a healing chamber in total darkness at 80% relative humidity and 22 °C, then acclimatised in the seedling greenhouse.
- System and substrate: seedlings raised in 200-cell plastic trays; transplanted into greenhouse soil (a sandy-clay Rhodic Paleudult, organic matter 0.69%, pH 5.9) on beds with black plastic mulch and drip irrigation; 0.5 m between plants and 1.0 m between rows; single stem.
- Nutrition: weekly fertigation (each week’s dose split into three applications) from 7 days after transplanting, changing formula by stage: 10-50-10 (7 to 30 days), 13-08-24 (31 to 60 days) and 08-07-40 (61 to 120 days), with calcium and magnesium supplements and boric acid. Totals per plant: 7.70 g N, 3.33 g P, 18.55 g K, 7.00 g Ca, 1.30 g Mg and 0.114 g B.
- Design: randomised complete block design, 2 × 2 factorial (cultivar × grafting), six blocks; 24 plots of ten plants (240 plants, 60 per treatment), with the four central plants of each plot measured for yield. Wilt was counted on all plants. ANOVA with Tukey’s test at p ≤ 0.05.
- Results: wilt incidence 0% grafted, 100% ungrafted Ravena, 86.7% ungrafted Grazianni. Fruit per plant 29.62 grafted, 24.94 ungrafted. Fruit mass 104.10 g and 94.80 g. Marketable fruit 1937.19 g and 1454.53 g per plant; total fruit 3078.61 g and 2373.20 g per plant. No significant cultivar × grafting interaction for the fruit traits.
- Funding and conflicts: the authors declare no financial support for this work and no conflict of interest.
- Publication: Frontiers in Horticulture 5:1966164, published 27 October 2026 (peer reviewed), https://doi.org/10.3389/fhort.2026.1966164. Licence: CC BY.
- Not reported in the paper: greenhouse temperature, humidity and CO2, light levels, the EC and pH of the fertigation, irrigation volumes, and the amount of the bacterium in the soil.
Links
- The study: Impact of grafting on yield and plant health of tomato varieties cultivated under protected subtropical climate
- The institution: Facultad de Ciencias Agrarias, Universidad Nacional de Asunción
References
- Godoy Medina, N. I., Santacruz Oviedo, V. R., Grabowski Ocampos, C. J., Enciso-Garay, C. R., & Burgos Rotela, R. (2026). Impact of grafting on yield and plant health of tomato varieties cultivated under protected subtropical climate. Frontiers in Horticulture, 5, 1966164. https://doi.org/10.3389/fhort.2026.1966164