Root Rot Complex in Western Canada where are we at with Fusarium, Aphanomyces, and Phytophthora Syama Chatterton, Sabine Banniza, Robyne Bowness, Mike Harding, Bruce Gossen, Debra McLaren November 8, 2017
Overview Root rot rot survey results from Western Canada Components of the root rot complex and differences between the organisms Reducing risks of root rot through management choices Diagnostic capacity in Western Canada for root rot pathogen testing Phytophthora stem rot in soybeans in Western Canada 2
Field surveys for root rot of pea and lentil from 2014-2017 Samples sent to Lethbridge for rating and analysis Diagnostic DNA tests for common pathogens 3
Disease severity rating scale 1 2 3 4 5 6 7 Healthy Moderate Severe 4
Disease incidence 100 Root rot survey results from 2014 2017 - incidence Pea 100 Lentil 80 AB SK 80 60 60 40 40 20 20 0 2014 2015 2016 2017 0 2015 2016 2017
Disease severity Root rot survey results from 2014 2017 - severity 7 6 Pea AB SK 7 6 Lentil 5 5 4 4 3 3 2 2 1 1 0 2014 2015 2016 2017 0 2015 2016 2017 6
% positive fields Percent SK fields positive for Aphanomyces 100 90 80 70 60 50 40 30 20 10 0 Black Dark Brown Brown 2015 2016 2016 pea Lentils 7
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% positive fields Other soilborne fungi in SK pea 100 90 80 70 60 50 40 30 20 10 0 Fusarium Virulent Weak Wheat
What does this mean for pea and lentil production in SK Root rots are here to stay with ~30-40% of fields with severe symptoms Impacts are less in dry years compared to wet years Lentils do seem to have lower severity than peas Yield impacts??? 10
Components of the root rot complex and differences between the organisms Two main pathogen groups of focus Aphanomyces euteiches highly aggressive on pea and lentil, long-lived resting spore Fusarium spp. - distributed widely F. avenaceum and F. solani most virulent species Other players include Pythium spp., Rhizoctonia, Ascochyta 11
Aphanomyces euteiches: First report in 2012/2013 Oomycete or water mould http://cronodon.com/images/ Only registered chemical = ethaboxam Very difficult to isolate using conventional methods, requires a DNA test 12
D. McLaren, AAFC Life Cycle of an Oomycete (Aphanomyces euteiches and Phytophthora sojae) Isoflavonoid exudates
Aphanomyces euteiches Highly specialized pathogen of legumes Fusarium avenaceum Generalist pathogen with broad host range Produces long-lived resting spores (oospores) Survives on stubble, and bridging from crop to crop Favoured by warm soil temps and excessive soil moisture Favoured by high soil temps and moderate soil moisture 14
Aphanomyces versus Fusarium? Yellowing and wilting of shoots Pinching of epicotyl, stops abruptly at soil line Lateral roots watery and honey-brown decay Shoots remain healthy Blackened tap root, starts at seed attachment Healthy lateral roots Aphanomyces Fusarium 15
Root rot most severe when 2 + pathogens present 16 Telsa Willsey, MSc Candidate
73% of fields positive for A. euteiches were also positive for at least 1 Fusarium species 17
Root rot infection stage Aphanomyces root rot: Infection can occur at any time in the growing season Most important factor is presence of soil moisture for zoospore infection Fusarium root rot: Most susceptible stage to infection seems to be at seedling stage Symptoms don t compound until late flowering Peas can sustain a fair amount of Fusarium root rot before yield impacted 18
Reducing risks of root rot effects through management choices Avoid planting peas and lentils in Aphanomycesinfested fields, get soil tested to confirm presence of Aphanomyces Quantify risk, sensitivity, and sampling pattern? Prolonged rotations away from susceptible hosts (peas and lentils) in infested fields How long is long enough? Quantify risk? Consider using a seed treatment that targets the root rot complex Which ones? How effective are they? 19
Use of seed treatments Metalaxyl lots of products registered for Pythium spp. Lots of actives against Fusarium spp. (e.g. fludioxonil, penflufen, fluxapyroxad etc.) Ethaboxam: Only product registered for A. euteiches, but for early season suppression Registered as a solo product, so must be used in combination with other seed treatments 20
Results A. euteiches + ethaboxam in the greenhouse Telsa Willsey, MSc Candidate
Telsa Willsey, MSc Candidate Early season suppression in pea when disease pressure was low 22
Yield (kg/ha) Aph Disease severity Root rot effect on yield is variable 4500 4000 3500 yield DS 6 5 3000 2500 2000 1500 1000 500 0 4 3 2 1 0 23
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CV Choice of cultivars? Assessed 20 cultivars all were equally susceptible to root rots, but some cultivars still yielded well 95 90 Striker 85 Royce Radius Barrhead 80 Cooper Patrick Saffron 75 Thunderbird Limerick Raezer Dakota 70 Lacombe 65 Golden Agassiz Amarillo Bronco Earlystar Meadow 60 Cutlass 55 Peace River 50 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 Yield (kg/ha) 26
Control options Rotation with other legume crops? Host range testing with Aphanomyces shows some pulse crops are more resistant than others 27
Host range testing of Aphanomyces Crop Disease reaction Oospores Peas Susceptible Yes Lentils Susceptible Yes Cicer milkvetch Susceptible Yes Dry bean Variable Few Alfalfa Variable Yes Chickpeas Resistant Few Sainfoin Resistant Few Faba bean Resistant? No Soybean Non-host No Fenugreek Non-host No 28
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Diagnostic capacity in Western Canada for root rot pathogen testing 20/20, Biovision, Discovery, Quantum BioSciences All offer molecular (DNA) test of roots and soil for Aphanomyces In-crop testing gives the most accurate results: Roots collected in mid-june to early-july Soil with roots growing in it are best 30
Diagnostic capacity in Western Canada for root rot pathogen testing No crop soil samples (post-harvest or pre-seeding) Sample soil from top 6 inches, low spots in field Some problems with quantitative detection from soils that don t have fresh oospores or low levels of oospores 31
Detection from soil works best on high risk fields 2.5 2.0 log10 oospores/g soil 1.5 1.0 0.5 0.0-0.5 2 3 4 5 Disease severity (greenhouse) 32
Take home messages Root rots are here to stay and are complex Field management is aimed at field avoidance and extended rotations away from peas and lentils Field testing is recommended and research is concentrating on developing robust molecular tests, but it s complicated Breeding for resistance is ongoing, but it s complicated 33
DISEASES ARE COMING
Phytopthora Rot of Soybean Primary causal agent: Phytophthora sojae Caused major losses in ON soybean since the mid-50 s; severe losses worldwide Emerging in Manitoba and western Canada but no information on the prevalence of Phytophthora rot or on races of P. sojae on soybean
Survey of MB Soybean Crops for Phytophthora Rot 2016: 38% of fields with symptomatic plants Confirmation of Phytophthora sojae by sequencing: no plants confirmed positive for P. sojae until molecular testing Confirmation of P. sojae ID in 38% of surveyed fields 2017: confirmation of P. sojae in 34 % of surveyed fields
Symptoms of Phytophthora rot Soybeans are susceptible to PRR at any stage of development Seed rot, pre- and post emergence damping off, reduced stands Empty spaces in field; remnants of dying seedling scattered throughout field Water soaked lesions on seedling that progress up the stem; yellowing of leaves Wilting of plants followed by death; leaves remain attached.
Symptoms of Phytophthora root and stem rot (cont d) Mid- to late season symptoms Stunting, root and stem rot Stem rot = chocolate brown canker that develops up the stem (most diagnostic feature) Internally, cortex and vascular tissue have a brown discolouration Plants wilt and leaves turn yellow as canker develops; canker may develop up one side of plant only Leaves droop and remain attached after plant dies.
Healthy soybean stem vs stem infected with Phytophthora sojae
Races and resistance Phytophthora exists in soils as populations of different races. There is genetic resistance available in soybean varieties Rps (resistance to P. sojae) resistance genes are used to characterize races of P. sojae Need to know what races are present to select the right variety
The value of resistance to P. sojae suseptible (L) and resistant (R) Single gene resistance is still an effective control measure for Phytophthora rot if growers know which pathotypes are present in their fields.
Management of Phytophthora in soybean Use cultivars with appropriate Rps genes Damage increases in areas of reduced tillage, especially no-till because these areas absorb more rainfall and are more easily saturated Crop rotation to reduce inoculum build-up Maintain good soil fertility Manage or avoid compacted fields or areas Seed treatment with fungicides and activity against Phytophthora
Technical Assistance Christine Vucurevich Carol Mueller, Scott Erickson Trina Dubitz Dustin Burke, Carol Pugh Cheryl Cho Telsa Willsey (MSc student) A lot of coop students 43