A new study by academics at the University of Hertfordshire, published in the scientific journal PLOS ONE, has shown that combining different types of crop resistance increases their efficiency at controlling a major plant pathogen which causes phoma stem canker on oilseed rape. Phoma stem canker causes losses to UK farmers of more than £95m (about $126 million) each year.
This is the first research to demonstrate that combining qualitative resistance and quantitative resistance in one cultivar can provide more effective resistance for the control of phoma stem canker than the use of either type of resistance on its own. Academics conducted this research using eight oilseed rape (Brassica napus) commercial cultivars in 13 different environments; 11 sites were in the UK and one site each in France and Germany.
The researchers found that environmental factors, such as temperature and rainfall, can affect the severity of phoma stem canker on oilseed rape and have shown, for the first time, that commercial cultivars with combined resistance (qualitative R gene-mediated and quantitative resistance) are less sensitive to a changing environment and therefore better at protecting the oilseed rape plants from phoma stem canker.
The study also demonstrated that increased severity of stem canker was associated with increased rainfall during the phoma leaf spot development stage and increased temperature during the stem canker development stage. This can have implications for farmers in helping them to know when it might be better use fungicides to protect their crops.
Yongju Huang, lead author on the study, says: “Phoma stem canker poses a high economic risk to oilseed rape production in the UK since it can greatly reduce the seed yield and quality. It is a big challenge to breeders to select cultivars with effective, stable resistance and a big challenge to growers to maintain the yield in a changing environment. This study will help to improve the sustainability of oilseed rape production.”
In the UK, oilseed rape is the third most important arable crop with a total of 2.2M tons harvested in 2017. It is the third largest source of vegetable oil worldwide and widely used as animal feed. However, there are three main diseases, all with a worldwide distribution, which affect oilseed rape and cause around 15 percent crop yield losses worldwide each year. One of these, phoma stem canker, causes losses to UK farmers of more than £95m per year.
Effective control of crop diseases is important for food security. The control of crop disease affecting oilseed rape is often done using chemical fungicides. However, these have an additional cost to farmers and they can easily lose their effectiveness due to the development of fungicide-insensitivity in pathogen populations.
Crop resistance can be used instead of fungicides to control the spread of crop diseases and using cultivar resistance against pathogens is one of the most economical and environmentally friendly methods for control of crop diseases. Two types of resistance used to control crop diseases are quantitative resistance (QR) and qualitative resistance. QR is usually controlled by several minor genes whereas qualitative resistance is usually controlled by single dominant resistance (R) genes. R gene-mediated resistance is race-specific and therefore not effective in protecting the crop when new pathogen races develop. QR is race non-specific but cannot provide effective protection when a large numbers of pathogen races are present in an environment favorable for disease development. Combining different types of resistance can provide better disease control.