Dr. Carmen Murphy, Plant Pathologist, Montana State University
Pulse crops such as lentil and dry edible pea have been an excellent rotation crop in dryland Montana, as well as other states and provinces in North America. This is due both to benefits to the cropping system such as nitrogen fixation, low water use, and breaking up pest and disease cycles in wheat as well as increasing farm profitability. In years with high pea and lentil prices, growers prefer to plant pulse crops due to the excellent return on investment. With frequent cropping of pulse crops, however, there has been a rise in the reports of root rot problems in dry pea and lentil fields. Multiple pathogen species can contribute to root rot issues on pulses, so it is referred to as a ‘root rot complex’. One of the major players in this complex, Aphanomyces euteiches, which causes Aphanomyces root rot, is particularly difficult to manage. The pathogen produces spores that can survive for many years in the soil and there are limited management options available for pulse growers. Below ground symptoms include root browning, root constriction, fewer nodules, smaller nodules, and a reduction in lateral roots (Figure 1).
Aphanomyces root rot affects several legumes including dry pea, lentil, alfalfa, clovers, and some bean varieties. Symptoms to look out for in the field are yellowing starting at the soil line, stunted plants, and dead plants. Plants should then be dug up to look for root rot symptoms. Environmental factors influence disease progression and initially root rot is often unevenly distributed in fields. Aphanomyces root rot is generally worse in years with warm spring conditions and high soil moisture. Other factors have been associated with the disease, these include high soil clay content, soil compaction, high organic matter, high soil nitrogen, low soil potassium, and low soil pH.
Diversifying rotations to include plants that are not susceptible to Aphanomyces root rot helps to manage root rot problems. To explore if there were certain plants that helped to reduce disease more than others, greenhouse trials were set up where soil was spiked with Aphanomyces spores, and a variety of plant species were grown (Figure 2). Following these plant species, the disease was baited out with dry pea, and root rot symptoms were rated.
Growing legumes that are susceptible to Aphanomyces root rot, ‘host plants’, led to more disease on subsequent dry pea plants compared to cereals, oilseeds, flax, brassicas, and weed species. Austrian winter pea (AWP) was affected by the pathogen under the warm greenhouse condition, however, in the field it is often too cold when AWP is growing for Aphanomyces root rot to establish. The ‘oat’ rotation was noticeably successful at reducing disease on dry pea in these controlled conditions. There is a compound in oat that causes the root rot spores to break open and disintegrate, decreasing the longevity of the pathogen. In field trials conducted in other states where oat was grown prior to pea, a reduction of root rot was found compared to treatments where oat was not grown.
It is critical to manage Aphanomyces root rot with crop rotation as that is the primary means of control. While the seed treatment ethaboxam (INTEGO® Solo from Valent®) has been labelled for use in multiple US states for Aphanomyces root rot, disease suppression in pulse fields has been inconsistent, and the treatment does not last the entire growing season. Future work with Aphanomyces root rot includes testing for additional fungicides / treatments with efficacy, the use of essential oils for disease management in organic systems, and collaborations with researchers who are working towards finding resistance in dry pea and lentil germplasm for use in breeding programs.
Acknowledgements: This research was made possible through funding from the Specialty Crop Block Grant from the Montana Department of Agriculture.
Author Bio:
Dr. Carmen Murphy is an Assistant Research Professor of Plant Pathology at the Regional Pulse Crop Diagnostic Lab and the McKelvy Extension Plant Pathology Lab at Montana State University. Her research is focused on the soilborne diseases of dry pea, lentil, and chickpea. 1911 W. Lincoln St, Marsh Labs, Lab 21, Bozeman, MT, 59717-3150. Phone: (406)-994-5162 | Email: carmenmurphy@montana.edu.
Published February 22, 2024
