Development of Yield Loss Assessment Model for Potato Late Blight Disease in Korea Md. Aktaruzzaman and Byung-Sup Kim Department of Plant Science, Gangneung-Wonju National University, Gangneung 25457, Korea Abstract Materials & Methods Table 1. Fungicide spray programs with applied rate & interval day Results References 1. James, W. C. 1974. Assessment of plant disease and losses. Annu. Rev. Phytopathol. 12:27-48 2. Kim, D.S., Park, H.C., Chun, S.J., Yu, S.H., Choi, K. J., Oh, J. H., Shin, K.H., Koh, Y.J., Kim, B. S., Hahm, Y. and Chung, B.K. 1999. Field performance of a new fungicide ethaboxam against cucumber downy mildew, potato late blight and pepper phytophthora blight in Korea. Plant Pathol. J. 15(1): 48-52. 3. Shaner G. and R. Finney. 1977. The effect of nitrogen fertilization on the expression of slow- mildewing in Knox wheat. Phytopathology 36: 1307-1311. Location: Gangneung Wangsan Date of Potato Planting: 2 May, 2014 and 27April, 2015 Plot Size: 5m x 7m & Replication: 03 Cultivars Name: Dubaek & Superior BLITECAST System: According to Krause et al. (1975) Date of cumulative disease severity value exit 18: 8 June, 2014 and 18 June, 2015 Spraying started: 13 June, 2014 and 23 June, 2015 (Farmer Schedule: 16 June, 2015) First Disease Observed: 20 June, 2014 and 29 June, 2015 Disease severity: Evaluated according to the following formula given by Kim et al.(1999) Disease severity (%)= {(4a+3b+2c+1d)/4(a+b+c+d+e)}x 100 Where, a= number of leaf with >75% of leaf area infected and stem partially decayed, b= number of leaf with 50.1~75% of leaf area infected, c= number of leaf with 25.1~50% of leaf area infected, d= number of leaf with 0.1~25.1% of leaf area infected, e= number of leaf with no disease Late blight caused by Phytophthora infestans is the major destructive and the most serious fungal disease of potato. Experiments were conducted during the years 2014 and 2015 at Gangneung alpine area of Korea to assess late blight disease severity and determine yield losses for the development of yield loss assessment model. The dynamics of late blight severity were monitored in Dubaek and Superior potato varieties with application of different fungicides spray schedule according to BLITECAST system. Forty linear regression lines were fitted with two years data for Critical point model, Multiple point model and AUDPC model. For 2014 experiment, 77 DAP was critical stage for late blight in both cultivars. Critical point model was: incase of Dubaek Y= 7.6+1.55X (R 2 = 0.84); incase of Superior cultivar Y= 8.88+0.98X (R 2 = 0.69). Multiple point model was: incase of Dubaek cultivar Y= - 17.59+36.72*V1+13.12*V2-1.09*V4 (R 2 = 0.84) for disease severity, Y= -61.29+48.51*V7-13.73*V9 (R 2 = 0.97) for disease increment; incase of Superior cultivar Y= -9.77- 67.4*V1+0.97*V2+3.49*V5 (R 2 = 0.95) for disease severity, Y= 9.46+6.83*V6+7.60*V7-11.61*V9 (R 2 = 0.98) for disease increment. AUDPC model was: for Dubaek cultivar Y= 8.57+0.05X (R 2 = 0.83); for Superior cultivar Y= 11.05+0.03X (R 2 = 0.64). For 2015 experiment, 85 DAP & 78 DAP was critical stage for late blight in for Dubaek and Superior cultivar respectively. Critical point model was: incase of Dubaek cultivar Y= 3.46+5.45X (R 2 = 0.63); incase of Superior cultivar Y= 1.04+9.86X (R 2 = 0.91). Multiple point model was: incase of Dubaek cultivar Y= -17.59+36.72*V1+13.11*V2-1.1*V4 (R 2 = 0.97) for disease severity, Y= 14.94+11.71*V5+9.45*V6-12.08*V7 (R 2 = 0.97) for disease increment; incase of Superior cultivar Y= 0.68+68.15*V1-26.85*V2-0.21*V4 (R 2 = 0.99) for disease severity, Y= 9.46+6.83*V6+7.60*V7-11.61*V9 (R 2 = 0.92) for disease increment. AUDPC model was: for Dubaek cultivar Y= 9.08+0.02X (R 2 = 0.46); for Superior cultivar Y= 8.92+0.43X (R 2 = 0.43). 2014 for Dubaek 2015 for Dubaek Treatments Spray programs Spraying interval (Days) Treatments Spray programs Spraying interval (Days) T 1 Cl-Cl-Dm-Dm-Cm+Mp 10 T 1 Cl-Cl-Dm-Dm-Cm+Mp 10 T 2 Fz-Fz-Dm-Dm-Cm+Mp 10 T 2 Cz-Cz-Dm-Dm-Cm+Mp 7 T 3 Fx-Fx-Dm-Dm-Cm+Mp 7 T 3 Fx-Fx-Dm-Dm-Cm+Mp 7 T 4 Control - T 4 Control - T 5* Mn-Mn-Mn-Dm-Dm- Cm+Mp 7 2014 for Superior 2015 for Superior T 1 Fz-Fz-Dm-Dm-Cm+Mp 7 T 1 Cl-Cl-Dm-Dm-Cm+Mp 7 T 2 Cz-Cz-Dm-Dm-Cm+Mp 10 T 2 Fz-Fz-Dm-Dm-Cm+Mp 10 T 3 Fx-Fx-Dm-Dm-Cm+Mp 7 T 3 Fx-Fx-Dm-Dm-Cm+Mp 7 T 4 Control - T 4 Control - T 5* Mn-Mn-Mn-Dm-Dm- Cm+Mp 7 Mn= Mancozeb (40g/20L); Dm= Dimethomorph (20g/20L); Cm+Mp= Cymoxanil + Mandipropamide (20ml/20L); Cl= Chlorothalonil (33g/20L); Fz= Fluazinam (10ml/20L); Cz= Cyazofamid(10ml/20L); Fx= Famoxadone (20ml/20L). T 5*= Farmer schedule Yield loss: Calculated using the following formula: YL = [(Yh-Yt)/Yh]*100 Where, YL = yield loss per cent, Yh = highest yield obtained among the treatments and Yt = yield obtained from a treatments Critical Point Model: These are based on the presumption that measuring disease at a critical stage of crop’s growth can drive the yield loss relation ship. y= ax+b Where, y= Yield loss (%), x= Disease severity, a & b = parameters Multiple-point models: According to James (1974) The general form of the regression equation is Y = a + b1X1+b2X2 + ... + bnXn where Y is the loss in yield and Xn, = the amount of disease measured at the nth assessment Time.b1…bn= partial regression coefficients for the first and nth assessment time AUDPC model : Using following formula given by Shaner and Finnay (1977) Where “t” is the time of each reading, “y” is the percent of affected foliage at each reading and “n” is the number of readings. Parameter: Disease Severity Variety: Superior Parameter: Disease increment Variety: Superior Equation y= -9.765-67.394*V1+0.967*V2+3.498*V5 Equation y= 9.459+6.828*V6+7.602*V7-11.605*V9 r 2 =0.953 Standard Error of Estimation: 5.326 r 2 = 0.978 Standard error of estimation: 2.643 Treatments a Disease severity (%) AUDPC Yield (kg/20 plants) Yield (t/ ha) Yield loss (%) 63 DAP b 70 DAP 77 DAP 84 DAP 91 DAP T 1 0.3 1.6 4.3 6.0 9.7 118.18 7.7 24.0 24.1 T 2 0.3 1.2 3.7 5.8 8.7 106.17 8.5 26.6 15.8 T 3 0.1 0.6 2.5 3.6 5.8 67.90 10.1 31.6 - T 4 4.2 19.3 29.2 48.6 75.3 957.48 8.4 15.1 52.2 Table 2. Effects of different fungicide spray regimes on disease severity (%), AUDPC, yield and yield loss (%) of potato due to late blight infection on Dubaek potato variety at Gangneung alpine area of Korea in 2014 a treatments are represented in Table 1. b days after planting. Table 3. Effects of different fungicide spray regimes on disease severity (%), AUDPC, yield and yield loss (%) of potato due to late blight infection on Superior potato variety at Gangneung alpine area of Korea in 2014 Treatments a Disease severity (%) AUDPC Yield (kg/20 plants) Yield (t/ ha) Yield loss (%) 63 DAP b 70 DAP 77 DAP 84 DAP 91 DAP T 1 0.3 1.8 6.2 7.2 10.9 145.72 10.9 34.0 10.3 T 2 0.2 4.9 11.8 12.2 16.8 269.50 7.2 22.4 40.9 T 3 0.2 1.0 3.0 3.7 6.3 77.0 12.1 37.9 - T 4 4.6 36.9 48.4 72.6 95.5 1456.0 5.3 17.6 53.6 a treatments are represented in Table 1. b days after planting. 63 DAP Disease severity (%) 0 1 2 3 4 5 Yield loss (%) 0 10 20 30 40 50 60 Dubaek y = 9.98x + 10.763 R² = 0.826 Superior y = 8.3152x + 15.182 R² = 0.519 70 DAP Disease severity (%) 0 10 20 30 40 Yield loss (%) 0 20 40 60 Dubaek y = 2.1865x + 10.617 R² = 0.8265 Superior y = 1.152x + 13.355 R² = 0.6215 77 DAP Disease severity (%) 0 10 20 30 40 50 60 Yield loss (%) 0 10 20 30 40 50 60 70 Dubaek y = 1.5536x + 7.605 R² = 0.8363 Superior y = 0.998x + 8.8855 R² = 0.6924 84 DAP Disease severity (%) 0 20 40 60 80 Yield loss (%) 0 20 40 60 Dubaek y = 0.9148x + 8.3878 R² = 0.8287 Superior y = 0.6125x + 11.547 R² = 0.6289 91 DAP Disease severity (%) 0 20 40 60 80 100 Yield loss (%) 0 10 20 30 40 50 60 Dubaek y = 0.5917x + 8.3062 R² = 0.8294 Superior y = 0.4704x + 10.971 R² = 0.6232 V1= % disease severity at 63 DAP V6= % late blight increment at 63-70 DAP V2= % disease severity at 70 DAP V7= % late blight increment at 70-77 DAP V3= % disease severity at 77 DAP V8= % late blight increment at 77-84 DAP V4= % disease severity at 84 DAP V9= % late blight increment at 84-91 DAP V5= % disease severity at 91 DAP Parameter: Disease severity Variety: Dubaek Parameter: Disease increment Variety: Dubaek Equation y= -10.758-80.309*V1+5.324*V5 Equation y= -61.296+48.506*V7-13.727*V9 r 2 = 0.840 Standard error of estimation: 15.13 r 2 = 0.967 Standard error of estimation: 6.837 Parameter: Disease severity Variety: Dubaek Parameter: Disease increment Variety: Dubaek Equation y= -17.588+36.723*V1+13.117*V2-1.095*V4 Equation y= 14.938+11.713*V5+9.445*V6-12.08*V7 r 2 = 0.97 Standard error of estimation: 3.102 r 2 = 0.97 Standard error of estimation:3.59 Parameter: Disease severity Variety: Superior Parameter: Disease increment Variety: Superior Equation y= 0.678+68.145*V1-26.85*V2-0.208*V4 Equation y= 8.485+4.428*V5+5.327*V6-7.249*V7 r 2 = 0.99 Standard error of estimation: 0.686 r 2 = 0.93 Standard error of estimation:5.82 V1= % disease severity at 78 DAP V5= % late blight increment at 78-85 DAP V2= % disease severity at 85DAP V6= % late blight increment at 85-92 DAP V3= % disease severity at 92 DAP V7= % late blight increment at 92-99 DAP V4= % disease severity at 99 DAP AUDPC Model AUDPC 0 200 400 600 800 1000 1200 1400 Yield loss (%) 0 20 40 60 Dubaek y = 0.0463x + 8.5702 R² = 0.8298 Superior y = 0.0311x + 11.053 R² = 0.6448 Table 5. Effects of different fungicide spray regimes on disease severity (%), AUDPC, yield and yield loss (%) of potato due to late blight infection on Dubaek potato variety at Gangneung alpine area of Korea in 2015 Table 4. Multiple point Model for Dubaek and Superior potato variety in 2014 experiment Treatments a Disease severity (%) AUDPC Yield (kg/20 plants) Yield (t/ha) Yield loss (%) 78 DAP b 85 DAP 92 DAP 99 DAP T 1 0.7 1.7 5.3 8.6 81.3 8.8 27.6 22.29 T 2 0.6 1.1 3.6 6.3 57.2 10.0 31.3 12.02 T 3 0.3 0.7 1.3 3.5 28.0 11.4 35.5 - T 4 2.5 4.5 56.6 98.4 781.3 8.5 26.5 25.51 T 5* 0.5 1.2 3.2 5.8 53.0 10.5 32.8 7.62 Table 6. Effects of different fungicide spray regimes on disease severity (%), AUDPC, yield and yield loss (%) of potato due to late blight infection on Superior potato variety at Gangneung alpine area of Korea in 2015 a treatments are represented in Table 1. b days after planting. T 5* =Farmers Schedule. Treatments a Disease severity (%) AUDPC Yield (kg/20 plants) Yield (t/ha) Yield loss (%) 78 DAP b 85 DAP 92 DAP 99 DAP T 1 0.9 1.8 4.5 6.1 68.7 12.6 39.3 11.92 T 2 1.4 2.9 6.7 8.9 104.7 11.9 37.3 16.36 T 3 0.4 1.0 2.7 5.2 45.4 14.3 44.6 - T 4 3.1 6.0 60.6 99.5 58.3 10.0 31.1 30.14 T 5* 0.9 1.8 4.1 6.3 66.5 12.4 38.9 12.85 Table 7. Multiple point Model for Dubaek and Superior potato variety in 2015 experiment 85DAP Disease severity (%) 0 2 4 6 Yield loss (%) 0 5 10 15 20 25 30 35 Superior y = 5.2099x + 0.1872 R² = 0.8967 Dubaek y = 5.4496x + 3.4608 R² = 0.6305 78 DAP Disease severity (%) 0 1 2 3 Yield losss (%) 0 5 10 15 20 25 30 35 Superior y = 9.8649x + 1.0351 R² = 0.9103 Dubaek y = 8.8389x + 5.3562 R² = 0.5689 92 DAP Disease severity (%) 0 20 40 60 Yield loss (%) 0 5 10 15 20 25 30 35 Superior y = 0.365x + 8.5158 R² = 0.7201 Dubaek y = 0.3011x + 9.2724 R² = 0.4686 99 DAP Disease severity (%) 0 20 40 60 80 100 Yield loss (%) 0 5 10 15 20 25 30 35 Superior y = 0.2175x + 8.7742 R² = 0.6989 Dubaek y = 0.1709x + 9.2979 R² = 0.4532 a treatments are represented in Table 1. b days after planting. T 5* =Farmers Schedule . AUDPC Model AUDPC 0 200 400 600 800 1000 Yield loss (%) 0 5 10 15 20 25 30 Superior y = 0.0205x + 8.9295 R² = 0.4365 Dubaek y = 0.022x + 9.0759 R² = 0.4671 Fig. 1. Critical point models of yield loss (%) by late blight disease severity (%) at various days after planting 63 DAP, 70 DAP, 77 DAP, 84 DAP, and 91 DAP for Dubaek ( ) & Superior ( ) potato variety at Gangneung alpine area of Korea in 2014. Fig. 2. Regression models of yield loss (%) by AUDPC for Dubaek ( ) & Superior ( ) potato variety at Gangneung alpine area of Korea in 2014. Fig. 2. Regression models of yield loss (%) by AUDPC for Dubaek ( ) & Superior ( ) potato variety at Gangneung alpine area of Korea in 2015. Fig. 1. Critical point models of yield loss (%) by late blight disease severity (%) at various days after planting 78 DAP, 85 DAP, 92 DAP, and 99 DAP for Dubaek ( ) & Superior ( ) potato variety at Gangneung alpine area of Korea in 2015.