Egerton University pioneers grafting method to fight bacterial wilt in tomatoes

ANNE MWALE- KNA 

Standing next to a tray of tiny tomato plants, Professor Joshua Otieno Ogweno carefully uproots one, picks up a razor blade, slices it in half, then uproots another plant and repeats the process. 

The Associate Professor in the Department of Crops, Horticulture, and Soils at Egerton University then uses a plastic rope to bind the two pieces together. 

“The top part is the scion, and the bottom part is the rootstock. Although the plants look the same, they’re from two different tomato varieties. We leave the new plant for two days to heal. If it wilts, we know it hasn’t healed,” he explains. 

Professor Ogweno, who is also the Kenyan Director at Egerton University’s Confucius Institute, explains that the grafted plants are then placed in a healing chamber for three weeks before being planted in a greenhouse. 

He notes that in 2019, researchers at Egerton University discovered that bacterial wilt (Ralstonia solanacearum) had be come a major challenge for most tomato farmers. 

Agronomists learned of a Chinese tomato variety known as Wells that is tolerant to bacterial wilt. This tomato plant can grow up to 18 feet, develops deep roots, and extends the harvest period from the usual three months to nine or ten months. 

“The solution involves grafting a scion from the commercial Anna F1 tomato variety onto the Wells variety rootstock, which is highly tolerant to bacterial wilt. 

This method produces resilient plants that mature earlier and yield more fruit compared to ungrafted plants,” he says. 

He adds, “We discovered it was advisable to use a resistant rootstock against soil-borne dis eases like bacterial wilt. Wells tomato variety is highly tolerant to bacterial wilt and its root stock has been used in Asian coun tries in the management of the disease.” 

Professor Ogweno affirms that grafting helps control tomato pests and diseases such as nematodes, fusarium as well as bacterial wilt which is a major challenge to most farmers. 

Tomato bacterial wilt, he said, is caused by a bacterium Ralstonia solan acearum, formerly known as Pseudomonas solan acearum. 

The pathogen has different races, each of them unique and each of them attacking different plants. 

The Don explains that tomato bacterial wilt is mostly caused by the Race I strain, which has a wide host range and can survive in the soil for a long period of time. He elaborates that Race 1 strains are highly variable in their genotype and aggressiveness on tomato. 

Some highly aggressive strains he observes, can cause severe symptoms, even on “resistant” varieties.

“Bacterial wilt of ten happens where plants have been cut, injured or weakened by insects or simply by cultivation. This bacterium lives in the soil and will work its way quickly through the roots and up the stem of the plants, preventing water and nutrients from reaching the leaves causing the death of the plant,” he elaborates. 

Professor Ogweno dis closed that Egerton University, in collaboration with Nanjing Agricultural University and the Confucius Institute, through an initiative, dubbed ‘Empowering Rural Youth through Innovative Horticultural Solutions in the Tomato Value Chain,’ has introduced an advanced grafting technology on trial basis in Nakuru, Kisumu and Nyandarua Counties to boost yields and manage bacterial wilt disease in greenhouse tomato. 

“Through the project funded by the International Fund for Agricultural Development (IFAD) we have trained over 4,000 farmers on green house tomato farming and grafting. 

“We are currently working with 14 farmers in conducting trials on tomato root stocks that are resistant to bacteria wilt. We intend to move to all the 47 counties once the trials are successful,” explains Don. 

He pointed out that the core objective of the project is to bolster food security and nutrition, reduce poverty among small holder farmers.