Helping Growers Succeed by Combating Disease Pressures

At De Ruiter™, we have been at the forefront of hybrid seed development and resistance breeding since 1946 and are building on our heritage. Today, we are vigilantly detecting emerging diseases around the world that can cause large-scale, economic damage, so we’re able to react quickly to develop new varieties with additional resistances. This ensures we can bring insights to our customers so they can have confidence in De Ruiter products. Below we’ve outlined a few important diseases and the dedicated innovation invested in De Ruiter seeds to help minimize pressure so our growers can grow a masterpiece. 

Cladosporium fulvum

Latin name: Passalora fulva
Crops it affects: Tomato
Resistance code: Ff

Cladosporium is widespread across the globe and is most prevalent in protected heated growing systems in early spring and late autumn. Optimal growth occurs at humidity greater than 85% and at temperatures between 71-75°F (22-24°C).  Pale greenish-yellow spots, usually less than 0.6 centimeters, form on the upper sides of leaves and olive-green to brown, velvety mold forms on the lower leaf surface below the leaf spots. This pathogen causes the leaves to wither and die, decreasing yield.

De Ruiter research teams worked hard to develop seed varieties with resistance to this disease, and in 1975, De Ruiter launched the first tomato varieties with resistance to five strains (Ff:A,B,C,D,E = Ff;A-E) of Cladosporium. This is the resistance level available in almost all commercial varieties today. While there are many strains of Cladosporium identified, the fungus mutates easily. When new strains emerge, they sometimes become prevalent, while other times they disappear again. At De Ruiter, our breeders and researchers are collaborating to track these strains that cause significant economic damage in different areas around the world. We are working hard to develop new resistances that better protect our growers’ crops that will launch in the coming years. 

Fusarium crown & root rot

Latin name: Fusarium oxysporum f.sp. radicis-lycopersici
Crops it affects: Tomato
Resistance code: For

Fusarium crown and root rot strikes at the root and invades susceptible plants through natural openings created by emerging roots. Infected plants often show signs of stunting, loss of lower leaves, yellowing and discoloration of the vascular tissues. The disease can be carried over to new soil from infected plants, and is favored by cool temperatures, 50-68°F (10-20°C).

In the 1980s, Fusarium crown and root rot became a major issue for growers in North America and Europe. In 1988, De Ruiter was the first company to offer Fusarium crown and root rot resistance in commercial tomato varieties. In the following years the resistance was introduced in other segments with varieties such as Trend, Furon, Pronto, Katinka and Recento. Today, it is standard in our De Ruiter breeding program to have resistance to this disease in our innovative seed varieties.

Powdery mildew

Latin name: Oidium neolycopersici
Crops it affects: Tomato, pepper and cucumber
Resistance code: On

Powdery mildew occurs only on a plant's leaves and appears as yellow spots ranging from 0.3-1.25 centimeters in diameter that leave a white, powdery fungus on top. Once infected, the entire leaf shrivels and turns brown taking nutrients from the plant, limiting yields. The disease is more frequent when there are wide fluctuations of temperature and humidity, which makes the leaves wet.

De Ruiter introduced the first varieties resistant to powdery mildew in 1996. This disease has become more persistent in recent years, explained partly by changing grower practices and because artificial lighting creates the optimal climate conditions for powdery mildew. Because of this, resistance is becoming more important. De Ruiter currently has innovative intermediate resistance varieties available in most segments and our dedicated teams are working to bring high resistance varieties to market in the coming year.  

Tomato yellow leaf curl virus

Scientific name: Tomato yellow leaf curl virus
Crops it affects: Tomato
Resistance code: TYLCV

Tomato yellow leaf curl virus is one of the most damaging pathogens that impacts tomatoes, particularly in areas with a Mediterranean climate. While there are a number of different strains, most plants show stunted growth and leaves that curl upward with marginal yellowing. When infected, growers often experience reduced fruit production and could lose 100% of their crop with heavily infected plants.

At De Ruiter, we have resistance to TYLCV in many segments throughout our tomato varieties due to conventional breeding. In the coming year, we will be launching the first varieties with intermediate resistance to TYLCV within the medium-truss segment in hopes of significantly reducing the issues this disease creates for growers.

Phytophthora root rot

Scientific name: Phytophthora nicotianae
Crops it affects: Tomato
Resistance code: Pn

Phytophthora root rot exists as resting spores in the soil and is known to cause severe growth reduction, resulting in yield loss. The disease grows most rapidly at 77-83°F. Saturated soil and poor drainage can increase the spread of the fungus, as the spores swim in water-filled pores between soil particles. The disease symptoms include a stunted appearance and wilt, and cause a brown rot in the roots, located close to the crown.

Recent studies by our researchers showed that De Ruiter tomato rootstocks, as well as some of our cultural varieties, have intermediate resistance to Phytophthora nicotianae. Because it is an important disease in many areas, our team is using cutting-edge technology to further identify the genetics that will allow us to breed additional resistance into our future varieties to help our growers succeed.

From helping growers understand the measures they can take to combat diseases to breeding disease resistance into our varieties, we’re working to make sure our growers can grow quality, high-performing plants to help protect their income. We’re excited to pair our passion to serve with our unrivaled glasshouse experience, so our growers can grow a masterpiece.


All information concerning the products/varieties given orally or in writing by Monsanto or its employees or agents, including the information in this article, is given in good faith, but is not to be taken as a representation or warranty by Monsanto as to the performance or suitability of those products/varieties, which may depend on local climatic conditions and other factors. Monsanto assumes no liability for any such information. This information shall not form part of any contract with Monsanto unless otherwise specified in writing.