Institute of Ag Professionals

Transcription

1 Institute of Ag Professionals Proceedings of the 2012 Crop Pest Management Shortcourse & Minnesota Crop Production Retailers Association Trade Show Do not reproduce or redistribute without the written consent of author(s).

2 Jim Kurle, Department of Plant Pathology University of Minnesota St. Paul MN

3 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Managing Phytophthora root rots Managing Resistance Resources Questions

4 Phytophthora Root and Stem Rot Causal agent: Phytophthora sojae Kauf. & Gerd. First observed in 1948 in Indiana. Widespread in soybean growing areas of the US and worldwide (Canada, Australia, Queensland, & East Asia). 2 nd most damaging disease to soybean in north central US from Annual yield loss: 42,218,000 bu in US in 1998 Minnesota losses average ~ 1.0% of yield. On individual field basis losses of 50 to 60%.

5 Phytophthora sojae Host range -relatively narrow -soybean (Glycine max (L.) Merr.) is the only major host -causes disease on some lupine species Infects roots and stems, occasionally leaves Causes seed rot, damping-off, root and stem rot Especially damaging if wet conditions occur during early stages of plant development

6 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Integrated Management Questions

7 Temperature and Moisture Effect on Infection Rhizoctonia Fusarium Phytophthora Pythium Sudden Death Syndrome Fusarium (adapted from Grau et al.,2004; Hanson et al., 2000; Irmak et al., 2006, Meyer, 2011)

8 Phytophthora sojae Oospore Sporangium Zoospore

9 P. sojae Life Cyle cetes/pages/phytophthorasojae.aspx

10 Phaqytophthora Root Rot Seedling Rot & Damping Off

11 Disease Symptoms post-emergence damping-off root & stem rot

12 Field Symptoms

13 Race vs. Virulence Pathotype Race -a designation based on reaction of P. sojae isolate to 8 or 13 Rps genes Virulence pathotype -a list of Rps genes which are susceptible to the P. sojae isolate

14 Pathogenic Diversity of P. sojae Designated as races by differential virulence on 8 or 13 Rps genes 55 races identified using 8 Rps differentials, additional virulence pathotypes Increasing number of virulence pathotypes and adaptation to Rps genes-highly variable pathogen Complex distribution of pathotypes within any one field

15 Diversity : Horizontal and Vertical P. sojae within a single field is highly diverse. Location 1: 21 isolates belonging to 10 races and nine pathotypes were recovered Location 2: a total of 13 isolates of P. sojae belonging to nine races and three pathotypes P. sojae population within the root zone can be diverse. In a single soil sample: Isolate 1, able to defeat Rps1a, 3a, and 7; Isolate 2, defeats Rps1a, 1d, 1k, 3a; Isolate 3 defeats Rps1c and 7; and Isolate 4 defeats Rps1a, 1k, 4, 6, and 7. (Robertson et al., 2007)

16 Within Field Diversity of P. sojae Rps3a Rps1c Rps1k (Dorrance, 2007)

17 How do pathotypes originate? Mutation Occasional outcrossing Other mechanisms

18 Race vs. Virulence Pathotype Rps gene (s) Phytophthora sojae races (pathotypes) Rps1a R S S S S R Rps1c R R S R S R Rps1k R R R R S S Rps3a R R R S R R Rps6 R R R S R S Rps8 R R R R R R Race Pathotype 1 3 1a 4 1a, 1c 7 1a, 3a, a, 1c, 1k 31 1k, 6

19 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Managing Phytophthora root rots Managing Resistance Resources Questions

20 Phytopthora Races Found in Minnesota 1986 Resistance genes Rps1a R S S S S Rps1b R R R R S Rps1c R R S R S Rps1k R R R R S Rps3 R R R S R Rps6 R R R S R

21 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Managing Phytophthora root rots Managing Resistance Resources Questions

22 Phytophthora sojae in MN (2000) 55% MN soybean fields infected -232 isolates collected -18 races identified -race 3 (34%) & race 4 (20%) most frequent -51 isolates not corresponded to known races Cultivars with Rps1c, Rps1k, or Rps6 effective in southern MN: MG (maturity group) I & II cultivars Soybean production expanded in northern MN (Red River Valley): MG 00, 0, & I cultivars

23 Kandiyohi Chisago Traverse Mille Lacs Wadena Clearwater Phytophthora sojae Found in 2000 Kittson Roseau Lake of the Marshall Pennington Red Lake Woods Beltrami Koochiching Cook Polk Itasca St. Louis Lake Norman Mahnomen Clay Becker Cass Otter Tail Crow Wing Aitkin Carlton Grant Douglas Todd Morrison Pine Pope Big Stone Swift Lac Qui Chippewa Parle Yellow Medicine Renville Lyon Murray Redwood Stearns Meeker Wright Brown Waton wan Sibley Nicollet Sher burne Carver Scott Isanti Anoka Rice Dakota Wabasha Winona Rock Nobles Jackson Martin Faribault Freeborn Mower Fillmore Houston

24 Psojae Races in Minnesota in 2000 Race Pathotype Rps0 2 Rps0 Rps1b 3 Rps0 Rps1 4 Rps0 Rps1, Rps1c 6 or 7 Rps0 Rps1, Rps3, Rps4, Rps6 8 or 9 Rps0 Rps1, Rps4, Rps6 13 Rps0 Rps6 15 Rps0 Rps3 18 Rps0 Rps1c 21 Rps0 Rps1, Rps3 22 Rps0 Rps1, Rps1c Rps3, Rps4, Rps6 25 Rps0 Rps1, Rps1b Rps1c Rps1k 27 Rps0 Rps1b Rps1c Rps1k Rps 3, Rps4, Rps6 28 Rps0 Rps1, Rps1b Rps1k Rps4 31 Rps0 Rps1b Rps1c Rps1k Rps4, Rps6 45 Rps0 Rps1, Rps1b Rps1c Rps1k Rps4, Rps6 ND Rps0 Rps1, Rps1k ND Rps0 Rps1, Rps1c Rps6 ND Rps0 Rps1b Rps1k Rps3, Rps6 ND Rps0 Rps1, Rps1c Rps1k Rps4, Rps6 ND Rps0 Rps1c Rps1k Rps 3, Rps6 ND Rps0 Rps1, Rps1c Rps1k Rps3, Rps4, Rps6 ND Rps0 Rps1, Rps1b Rps1c Rps1k Rps3, Rps4 Rps6

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26 Change in number of Phytophthora sojae pathotypes identified in Minnesota Pathotype

27 Proportion of P. sojae Isolates Virulent on Major Resistance Genes

28 Rps Genes Defeated by Isolates found in Minnesota

29 The value of resistance to P. sojae susceptible on the left and resistant on the right (R) Malvick

30 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Integrated Management Questions

31 Qualitative Resistance Resistance genes (Rps genes) 14 Rps genes identified -Rps1a, Rps1b, Rps1c, Rps1d, Rps1k, Rps2, Rps3a, Rps3b, Rps3c, Rps4, Rps5, Rps6, Rps7, & Rps8 9 Rps genes deployed into commercial cultivars -Rps1a, Rps1b, Rps1c, Rps1k, Rps2, Rps3a, Rps4, Rps6, & Rps7

32 Partial Resistance Quantitative, race-nonspecific, highly heritable Tolerance, rate-limiting resistance, general resistance, field resistance No negative effect on yield Allows root rot development but limits damage compared to susceptible cultivars Better protection when plants were exposed to diverse P. sojae population under low-moderate disease pressure

33 Partial Resistance More durable than resistance (Rps genes) -non race-specific -not affected by shifts in race composition of P. sojae -exert no selection pressure on P. sojae population Why have not been widely used? -hard to incorporate into cultivars -polygenic, quantitative trait -identify QTLs before incorporating into cultivars

34 pp728/psojae/p_sojae.htm Hypocotyl Injection Method

35 Reaction Types Susceptible (S) Resistant (R)

36 Inoculum Layer Method 4-week process P. sojae isolate: grown on V8 juice agar in Petri dish at 25ºC for 2 weeks Planting seeds & apply inoculum layer -6 polystyrene pot with vermiculite -one intact agar culture/ pot, 5cm below seeds -10 seeds/ pot 3 weeks later, root rot rating

37 Inoculum Layer Method

38 Partial Resistance to P. sojae 1 to 2 3 to 4 5 to 6 7 to 8 9 to 10 1 to 2--- Healthy, no symptoms. 3 to 4--- Slight discoloration of secondary roots to first signs of pruning of secondary roots. 5 to 6--- Pruning of secondary roots to first appearance of lesions on primary root. 7 to 8--- Secondary roots essentially absent. Lesions present on primary root and tip pruning. 9 to 10-- Damping of seedling. Dead seedling. Rotted seed.

39 Root Rot Rating Root Rot Rating of 28 Soybean Cultivars Evaluated for Partial Resistance (P 0.05) 6.00 HIJ IJ JK 4.00 KL KL L L Cultivar

40 Phytopthora sojae Characteristic of the pathogen Biology & Nomenclature Status in Minnesota Resistance Resources Integrated Management Questions

41 Managing Phytophthora sojae Cultural practices: -crop rotation, soil drainage, tillage Planting resistant cultivars (Rps genes) Planting partially resistant cultivars Chemicals: metalaxyl -seed treatment, in-furrow application

42 Cultural Practices Crop rotation limited in effectiveness Persistence of oospores as inoculum Rapid response to favorable environmental conditions Limited number of cropping options

43 Planting Resistant Cultivars Increasing pathotype complexity. Increase in number of pathotypes compatible with Rps1a, Rps1c, Rps1k, Rps6. Effect of selection on prevalence of pathotype. Sole Reliance on Rps genes encourages populations of P. sojae virulent on most effective resistance genes.

44 Integrated Management Partial Resistance Effective after Emergence. Mefanoxam & Metalaxyl Effective Seed Treatments for Phytophthora. Combination Seed Treatment & Partial Resistance offer Promise.