New biocontrol method against stem rot in groundnut

Cuong Le, a researcher at Wageningen University, part of Wageningen UR, has made a promising discovery regarding the use of bacteria as a biological control method against the groundnut disease; stemrot. Groundnut is cultivated in over 100 countries with an annual production of 34.43 million metric tons. Between five and 25 percent of the groundnut plants are infected with stem rot every year in Vietnamese fields. Le did his fieldwork in Vietnam and found bacteria which have a positive influence on plant growth and on suppression of stem rot caused by the fungus Sclerotium rolfsii Sacc. He is positive about the potential of this discovery: “The bacteria will hopefully be on the market in Vietnam within three to four years, and can be used for biological control of stem rot by farmers.” Le will defend his PhD thesis at Wageningen University on 16 December 2011.

Groundnut is an economically important legume in many countries, with China being the main producer with some 14.3 million metric tons. The cultivation is limited by stem rot caused by the soil borne fungus S. rolfsii. Worldwide the groundnut yield loss due to stem rot is ten to 25 percent and Le’s survey in groundnut fields in Vietnam found that between five and 25 percent of the plants there are infected with S. rolfsii.

Current control methods of stem rot mostly rely on adapted cultural practices and the extensive use of fungicides, which may lead to fungicide resistance in the S. rolfsii population. To find a biological control method, Le carried out research into the efficacy of soil bacteria to suppress stem rot disease. He examined three bacterial genera: Pseudomonas, Chryseobacterium and Bacillus. Results show that Pseudomonas and Bacillus species in particular improve plant growth. Field experiments showed that Bacillus and Chryseobacterium species are effective in reducing stem rot disease.

Another part of Le’s research involved the genetic variation among S. rolfsii isolates from different fields. Le found that strains are genetically diverse and differ in morphology. This variation will make it more difficult to find a good strategy to inhibit stem rot. “The diversity in the pathogen population means that a combination of different methods will be required to control the disease,” explains the researcher.

To develop a good biological method against stem rot, more research is needed into the relationship between the facts that several bacteria improve plant growth and several inhibit stem rot. Le expects that in three or four years the bacteria can be used as a bio control method by farmers in Vietnam: “Bio control bacteria can be key components of an integrated approach to manage diseases of groundnut and improve the yield.”

The groundnut has an unusual name as it is a member of the bean family and is in fact a pod. The nut moniker came about to the fact that the plant develops its fruits - the pods - underground. After the flowers have been fertilized they wilt and the stem elongates into the soil and buries the fruit, which develops into underground pods.

Le obtained his bachelor degree at the Hue University of Agriculture and Forestry in Vietnam and started his research on the control of wilt diseases in groundnut and S. rolfsii as part of an MSc study at the same university. In 2008 he joined Wageningen University as a PhD student to do a PhD on the diversity and biological control of this causal agent of stem rot in groundnut. After his graduation Le will continue researching S. rolfsii at Hue University of Agriculture and Forestry. The PhD project is funded by the government of Vietnam.