Root rot is a major disease of dry bean across the Canadian prairies and is capable of causing significant yield losses due to reduced plant stands and compromised root systems. Control of root rot is difficult and cultivars with complete resistance have yet to become available. Acquiring information on the most common root rot pathogens is necessary in order to develop best management practices for this disease complex.
Traditionally, cultural methods have been employed to isolate and identify potential pathogens from diseased roots, but this is a relatively slow process. In recent years, DNA-based technologies have increased the specificity and sensitivity of pathogen detection. Such tools are already proving useful in identification and rapid detection of new and emerging pathogens and pests. DNA-based diagnostic techniques save both time and money in the identification process. A more rapid and accurate identification of the pathogens causing yield loss will enable producers to more efficiently grow and manage their dry bean crops.
To acquire detailed information on root rot pathogens in Manitoba, approximately 40 commercial bean fields were evaluated per year for the incidence and severity of root rot. Over the past four years (2013-2016), 100% of the bean fields examined have root rot. Root diseases are rated on a scale of 0 (no disease) to 9 (death of plant) and an average root rot severity rating above 4 (i.e., symptoms were present on 50% of the root system) would have had a detrimental effect on crop yield. In 2013, 2014 and 2016, 85%, 78% and 93% of bean fields, respectively, that were surveyed had an average root rot severity above 4, which indicates that root rot would have had a significant impact on yield during those years. From 2013 to 2016, approximately 25 bean fields were surveyed for root diseases in the main production areas of southern Ontario. Root rot was severe, with 100%, 96%, 73% and 88% of surveyed fields having average root rot ratings above 4.
Fusarium root rot has been the most prevalent root rot disease in Manitoba and Ontario. Identification of the Fusarium spp. responsible for bean root rot has been ongoing. Through this work, Fusarium cuneirostrum was reported to be a causal agent of root rot disease in dry bean for the first time in Canada. A collection of isolates of the pathogenic species causing root rot of dry bean has been established with additional fungal isolates being assessed each year.
Molecular diagnostic procedures have been developed for a number of bean root rot pathogens, including F. cuneirostrum, and this work continues to enable the rapid, highly specific and very sensitive detection of the root rot pathogens in bean roots. This research will enhance the identification of bean root rot pathogens within a short timeline compared to classical methods that require days to weeks for the same results. Information on the common bean root rot pathogens is critical in order to screen for host resistance and design effective control measures.
Each year, the results of root rot surveys of commercial dry bean fields in Manitoba and Ontario have been published. Scientific publications are being prepared that identify new root pathogens of dry beans in Canada. This research has provided two postdoctoral fellows with experience in investigating the causes of root diseases in pulse crops and in developing new methodologies for rapid, accurate detection of root pathogens.
Project lead: Dr. Debra McLaren (204) 578-6561 firstname.lastname@example.org