Biofumigation is a holistic crop protection method that is based on incorporating brassica residues or seed meals that are rich in glucosinolates, for improving soil fertility and reducing pests, weeds and diseases. Whilst there are many benefits to using biofumigant plants, there is concern that the incidence and severity of the disease club root (Plasmodiophora brassicae) could be increased as a direct result of their use. Club root is a disease that infects members of the brassica family, such as oilseed rape, causing swolen roots and stunted growth. This project investigated the susceptibility of Brassica juncea (cv. Caliente 99 and cv. Vitasso), Eruca sativa (cv. Nemat) and Raphanus sativus (cv. Bento) to infection by club root when grown in soil infested with P. brassicae for 8 and 12 weeks. ISCI 99, Vitasso and Nemat developed significant clubbing symptoms after 8 weeks. However, Bento only developed mild disease symptoms after 12 weeks. After 8 or 12 weeks the biofumigant plants were then chopped and incorporated into the soil and oilseed rape (cv. Cabernet) were sown into the pots. Assessments of club root were made 11 weeks later to evaluate the effect of biofumigation on the development of club root on oilseed rape. Club root symptoms were more severe on oilseed rape plants following ISCI 99 and Vitasso regardless of the growing period. Oilseed plants grown after Bento had a similar severity of clubroot to those plants grown in infested soil that had not been previously used to grow brassica plants. In this experiment, there were no indications that club root was reduced by the biofumigation process.
Plant Solutions Ltd. currently supplies several species of brassica seed, including Brassica juncea (Indian mustard, marketed as Caliente 99®) and Eruca sativa (rocket, marketed as Nemat®) as green manures with biofumigant activity. Biofumigation is a holistic crop protection method that is based on incorporating brassica residues or seed meals that are rich in glucosinolates, for improving soil fertility and reducing pests, weeds and diseases. When the tissues of certain Brassica species are disrupted by mechanical damage, secondary metabolites known as glucosinolates are liberated from the cell vacuoles and become hydrolysed by myrosinases to release a variety of volatile compounds that include nitriles, isothiocynates (ITCs), thiocynates and oxazolidinethiones (Bjorkman, et al., 2011; Kirkegaard et al., 1993). In the face of increasing political pressure on reduced pesticide usage, biofumigation offers a multifaceted and sustainable crop management method for growers.
Whilst there are many benefits to using biofumigant plants, there is concern that the incidence and severity of the disease club root (Plasmodiophora brassicae) could be increased as a direct result of their use (Christianson, 2008). Club root is a disease that infects members of the brassica family causing swolen roots and stunted plant growth. The resting spores of P. brassicae are known to remain viable in the soil for 20 years or more. This disease is of particular concern to growers of oilseed rape and cabbage. The area of oilseed rape planted in the UK in 2008 was approximately 598,000ha (HGCA Planting Survey), with a total UK production of around 1.973M tons, making it the third most important crop in the UK. Club root is a disease of increased importance on oilseed rape crops (HGCA, 2011) but is not known whether the biofumigation process is having a positive or negative effect on the disease.
There is a limited amount of literature on the interaction between plants with high glucosinolate levels and club root. However, a study conducted in New Zealand revealed that sowing and then chopping and incorporating Brassica rapa (Turnip) in P. brassicae infested soil would reduce the severity of the disease in a subsequent planting of Cauliflower (cv. Visto) (Cheah et al., 2004). The authors attributed this effect to the concentration of isothiocynates, particularly 4-pentenyl ITC produced by B. rapa. In the same experiment, incorporation of B. napus (oilseed rape) residues was not found to reduce disease severity in cauliflower.
This project (completed October, 2012) had the following objectives: -
1. Determine whether B. juncea, E. sativa and R. sativus are suitable hosts for P. brassicae. If these species are not susceptible to P. brassicae, this would widen their availability in rotations on infested land. Conversely, if the biofumigant plants are susceptible, this knowledge would help avoid exacerbating an existing problem.
2. Determine whether the incorporation of residues from B. juncea, E. sativa and R. sativus effects subsequent infection of oilseed rape by P. brassicae. If the incorporation of residues from these species causes a reduction in club root in subsequent oilseed rape crops, this will present the company with a new opportunity for their use.
Technology Strategy Board, SPARK project
Harper Adams University
Plant Solutions Ltd