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Pythium Diseases of Carrots

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Pythium Diseases of Carrots Pythium Diseases of Carrots Mike Davis Dept. of Plant Pathology UC Davis Pythium • Has cellulolytic activity • Inhabits feeder roots • Inhibited by suberin and lignin • Wide host range • Relatively fast growing • Many do not produce zoospores Pythium differs from true fungi by: • Types of spores (oospores in Pythium) • Nuclei (diploid in Pythium) • Cell wall composition (cellulose in Pythium) • Types of flagella on zoospores (two types in Pythium) • Sterol production (Pythium must acquire from host) APS net Pythium sulcatum P. ultimum P. violae P. irregulare P. ultimum P. irregulare P. irregulare P. violae Effect of soil treatments Effect of methyl bromide fumigation CS (%) MeBr CS (%) None 10.6 a None 19 Metam 5.6 240 lbs/acre 1 MeBr 3.9 b Metalaxyl 1.8 Effect of metam Effect of metam through drip Rotovate + role CS (%) Dieback (%) PPM CS (%) Dieback (%) None 7.5 a 8 a 0 43 a 2 a 30 Gal/acre 8.0 a 4 a 250 19 b 3 a 60 Gal/acre 8.0 a 5 a 500 20 b 2 a Pythium species recovered from CS lesions (n=595) P. violae 60% P. sulcatum 16 P. ultimum 16 P. irregulare 5 P. cryptoirregulare 3 P. dissotocum <1 Plant Dis. 96:384-388. 2012 1991 2001 2011 P. violae 70% 20 88 P. sulcatum 0 15 4 P. ultimum 30 50 6 Symptomatic Asymptomatic hosts hosts Nonhosts carrot celery tomato alfalfa broccoli potato snap pea cowpea pepper lima bean wheat cotton Pythium violae table beet cucumber safflower radish spinach corn lettuce cantaloupe onion cabbage pumpkin chard barley onion cabbage watermelon eggplant parsnip oats ryegrain triticale Pythium sulcatum Plant Dis. 78:335-338. 1994 Effect of crop rotations on root dieback and Pythium Root dieback (%) Pythium cfu/g Trial 1 Trial 2 Trial 1 Trial 2 Fallow-carrots 2 a 3 a 22 a 16 a Carrots-carrots 5 ab 4 a 35 a 26 a Onions-carrots 1 a 3 a 16 a 19 a Barley-carrots 8 bc 2 a 134 b 53 a Alfalfa-carrots 9 c 9 b 112 b 37 a Cotton-carrots 1 a 8 b 44 a 51 a Plant Dis. 83:146-148. 1999 No relationship between CS and: pH 5.7-7.7 EC 0.79-2.82 millimhos/cm Total calcium 12.6 – 71.0 meq/100 g X-calcium 3.6 – 22.1 meq/100 g Moisture -10 kPa 7.5 – 19.0% Moisture -1500 kPa 3.1 – 7.0% Sand 60 – 77% Silt 9 – 24% Clay 8 – 16% OM 0.52 – 1.10% Plant Dis. 75:519-522. 1991 Cavity spot development CS incidence 14 2 12 R = 0.942 57 plants/m 33% 115 plants/m 35% 10 173 plants/m 31% CS 8 NS % 6 4 2 0 10 20 Weeks Nunez, MS Thesis, Fresno St 16 y = -3.60 + 0.67x r = 0.65 12 8 4 Cavity spot incidence spot Cavity incidence (%) 0 2 6 10 14 18 Weeks after planting Plant Dis. 75:519-522. 1991. Cavity Spot Variety Evaluations Cavity Spot Variety Trial 1992 Cultivar Source % Cavity Spot Nogales Bejo Zaden 62.8 Huron Sunseeds 62.4 Apollo Alf. Christianson 55.2 Avenger Petoseed 54.8 Apache Sunseeds 52.5 Caro Best Asgrow 51.2 Orlando Alf. Christianson 50.8 Sierra Northrup King 50.3 Flame Northrup King 47.8 Vita Sweet 711 Abbot & Cobb 44.6 CX 6146 Alf. Christianson 40.2 Vita Sweet 691 Abbot & Cobb 39.5 FMX 351 Ferry-Morse 38.0 XPH 87W335 Asgrow 35.3 Caro Choice Asgrow 35.2 Plato Alf. Christianson 32.7 Caro Pak Asgrow 32.6 FMX 350 Ferry-Morse 27.9 Six Pak II Harris Moran 27.7 HMX 5280 Harris Moran 25.8 Six Pak Harris Moran 23.0 Vita Sweet 781 Abbot & Cobb 20.1 Blaze Northrup King 19.8 Imperator 58 Alf. Christianson 15.8 LSD P=0.05 19.8 %CV 35.6 Incidence of Cavity Spot on Select Cultivars , 1997-1998 Entry Trial 1 Trail 2 Trial 3 2566B 2.7 de 21.5 bcde 3.1 a 3180C 13.8 abcde 0.8 e 1.2 c 3475A 26.6 a 24.5 bcd 3.4 a 4367A 7.5 bcde 80.3 a 17 a 5280B 14.9 abcd 17.8 cde 6274A 6.8 bcde 39.5 b 6333A 1.7 de 12.3 de 7.5 6355B 3.5 cde 34.3 bc 5.1 a 7254A 16.3 abc 21 bcde 7263A 1.2 e 0 e 7279B 6.3 bcde 0 e 5.9 a 7291B 19.1 ab 12.5 de 7322S 6.5 bcde 12.3 de 9304M 2.8 de 42.5 b 0.6 a HCM 2.5 de 4.5 de Dominator 11.6 bcde Six Pak 2.3 de Caro Pak 11.1 bcde 5 a Six Pak II 2.6 a Imperator 58 4 a Orlando Gold 2.8 a Pre- and postplant applications of metalaxyl on cavity spot Carrots with cs (%) (3 trials) Metalaxyl, lbs a.i./acre Preplant, 1 lb 20 % Preplant, 2 lb 17 Preplant, 4 lb 10 Split-postplant, 0.125 lb (8 appl.) 13 Split-postplant, 0.25 lb (8 appl.) 9 None 45 None vs metalaxyl 3/3 trials Preplant vs split 1/3 Preplant 1+2 lb vs split 2/3 Preplant 4 vs split 0/3 Split 1 lb vs split 2 lb 1/3 Preplant linear 3/3 Calif Ag 45 (No. 2):29-30. 1991 Single applications of metalaxyl Metalaxyl (2 lbs ai/acre) CS (%) None 32.0 a 45 days after planting 7.5 b 55 days after planting 10.5 b Alliette (phosphoric acid) trials CS (%) Aliette 1.4 kg product/ha 31 b Aliette 2.8 33 b Aliette 5.6 25 b Metalaxyl 2.2 kg ai/ha 6 a None 25 b Nunez, MS Thesis, Fresno St Cavity Spot Fungicide Trial, 2002 CS (%) None 57 a Ridomil-Gold 8 fl oz/A (3X) 40 bc Reason 0.27 lb ai/A (4X) 35 c Ranman 6 fl oz/A (4X) 36 c Phosgro 4 pts/A (3X) 47 ab CS Fungicide Trial, 2004 and 2005 CS (%) None 11 a 8 ab Ridomil-Gold 8 fl oz/A (3X) 8 a 11 b Reason 5 oz ai/A (4X) 4 b 8 ab Ranman 6 fl oz/A (4X) 8 a 2 a Fungicide Sensitivity Sensitivity to Ridomil-Gold Pythium cryptoirregulare resistant P. sulcatum somewhat tolerant P. irregulare sensitive P. ultimum sensitive P. violae sensitive Pythium cryptoirregulare Enhanced Degradation of Ridomil Gold Calif. Ag. 56(2):76-79. 2002 MITC (Vapam) Dissipation 0.8 0.6 No history Long history 0.4 Organic 0.2 Poor control MITC (mmol/kg) MITC 0 0 20 40 60 80 100 Time (hours) Conversion Efficiency (1 hour) Field/metam use (conversion to MITC) No history 95% Long history 93% Organic 93% Poor control 94% Biological agents: Bacillus species Pseudomonas species Trichoderma species Quantum 4000 Dagger Kodiak Stein A&B Microplex Plus Hurricane Zap Pseudomonas putida Pythium oligandrum (one of the better agents) P. sulcatum P. violae P. irregulare P. ultimum P. sulcatum Quantitative Real-time PCR Cavity Spot Models P. ultimum (68%) 18 2006 15 12 Incidence 9 of cavity spot (%) 6 3 0 0 30 60 90 120 150 180 Total Pythium population (cfu/g soil) 68% 18 2006 15 (r2= .78 w/o 68) 12 Incidence 9 of cavity spot (%) 6 3 0 0 5 10 20 30 40 50 Pythium sulcatum and P. violae (cfu/g soil) (69) (43) 12 18 2007 2007 15 10 12 8 Incidence of forking Incidence 9 6 (%) of cavity spot (%) 6 4 3 2 0 0 0 30 60 90 120 150 180 0 10 20 30 40 50 60 Total Pythium population (cfu/g soil) Pythium ultimum and P. irregulare (cfu/g soil) (69) (43) 18 2007 15 12 Incidence 9 of cavity spot (%) 6 3 0 0 1 2 3 4 5 6 Pythium sulcatum and P. violae (cfu/g soil) • Populations of total Pythium species do not predict cavity spot • Populations of P. violae and P. sulcatum may be important indicators of cavity spot but other factors are involved • Pythium-induced dieback may be related to populations of P. ultimum and P. irregulare • The occurrence of cavity spot is erratic Thank You!.
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