POTATO LATE BLIGHT EPIDEMIOLOGY AND EPIDEMIC ANALYSIS IN EGYPT

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1 ;; OTATO LATE BLIGHT EIDEMIOLOGY AND EIDEMIC ANALYSIS IN EGYT reface MOHAMED ALI FAHIM 1 AND AYMAN FARID ABOU-HADID 2 mohamedali@clac.claes.sci.eg Central Laboratory for Agricultural Climate,.O. Box 296, Imbaba 12411, Giza, Egypt (phone: ; fax: ) (Cairo, 20 th June 2004) otato (Solanum tuberosum L.) is one of the most important economic crops in Egypt. The total cultivated area was 73,473 feddans (Hectare = 2.38 Feddans) yielded about 604,423 tons at late summer (i.e Nili) plantation, 75,744 feddans yielded about 752,665 tons at summer plantation and 62,244 feddans yielded about 626,925 tons of potato tubers at winter plantation. otato area represents about 17% of the total vegetable area and about 1.5 % of the total cropped area in Egypt. otato late blight caused by hytophthora infestans (Mont.) de Bary is still am ong the most destructive of plant diseases. Under favourable environmental conditions, and in the absence of any control measures, this disease can destroy virtually 100% of the above-ground parts of susceptible cultivars. Infection efficiency is a function of the environmental conditions and the potato cultivar. Sever epidemics of late blight have emerged in 1999/2000, 2000/2001 and 2003/2004 growing seasons. An indicator variable for the occurrence of outbreak during the season based on the number of favorable days in terms of temperature and relative humidity during November to January. Weather conditions prevailing during potato-growing winter seasons were studied. Mild and warm nights allow the disease to become established on first-early cultivars. This build-up of inoculums early in the year leads to a tendency for blight to appear in later-planted potato crops in the area sooner than it does in other regions. Wet warm winter seasons were identified as important factors influencing development of the recent late blight epidemics in Egypt. The results of the present study show that disease incidence varied among seasons and different locations in most surveyed areas. The most affected area by late blight was at Giza, Behaira, Dakahliya and Ismailia. The highest severity of late blight in many fields indicated that these fields were grown under favorable weather conditions. 1 otato Late Blight Epidemiology Researcher, Central Laboratory for Agricultural Climate 2 Director of Central Laboratory for Agricultural Climate (CLAC)

2 Late blight disease distributions in Egypt Based on disease observations, the epidemic seasons late blight was shows in following maps: Disease rates (r) From the analysis of disease progress curves, late blight epidemic started shortly and progressed steadily in most of potato growing area in Egypt during epidemic winter seasons. The late-blight rates (r) in potato growing area in non-epidemic season were calculated and fall between However, during epidemic seasons, late-blight rates (r) were calculated and fall between From this analysis, the late blight rates during epidemic years were increased to highest value

3 during potato age from days after planting. The absolute daily rate was calculated for disease progess curves of late blight in different potato growing area between Based on disease data, the regression models were the most appropriate for description the disease progress data. The estimated r values are the slope of linearized y versus time x for disease models. Area under disease progress curves (AUDC) AUDC have been estimated by integrations the progress curves. Graphic Analysis programme has been used for the integrations. For the epidemics of late blight on the main potato growing area in Egypt, AUDC was calculated from the disease progress curve for each location. The AUDC in potato growing area at nonepidemic season 1998/1999 was ranged from 2.16 to 4.99 % in all of studied area. However, during epidemic seasons , AUDC was estimated between % in all of epidemic locations (Fig. 3-4). The integration equation has been formed in equation 1, 2 (for example) in Badrashin 1998/1999 & 1999/2000, respectively: in which the final gotten value divided by 120 (Length of season), multiple in 100 (Disease severities percent). AUDC 120 = n= (-0.001x x x x x x) = (1) = 599.5/120*100 = = 4.99 % AUDC = 120 n = 1 (-0.016x x x x x) = (2) = /120*100 = 0.25 = 25 %

4 Yield loses assessment and prediction There were three-disease assessment methods (i.e. Single-point model, Multiple-point, and area under the disease curve) were used and tested for yield loss assessment and prediction. The actual yield loss has been estimated from Agricultural Economic Annual Reports and from personal communication with farmers. 1. Single-point model The single-point model has been used the time (days after planting) to a certain disease severity level. The potato age has been divided into 3 stages, as 40-70, , and >100 days. The estimated losses (y) in yield which associated with progress curves were calculated. The equations were resulted as following: y = x 1 R 2 = (1) y = x 2 R 2 = (2) y = x3 R2 = (3) in which x 1, x 2, and x 3 are disease severity or a transformation of disease severity at age 40-70, , and >100, respectively, and the equations 1, 2, and 3 are prediction of yield loss at age 40-70, , and >100, respectively. 2. Multiple-point or Multiple Regression Model Multiple regression analysis to develop an empirical equation to relate yield losses directly to the epidemic using MINTAB analysis program. The growth season was divided into three stages, which mentioned above. The equation obtained from the multiple regressions is as follows: Y = x x x 3 R = 0.98 where Y is present tuber yield loss and x 1, x 2, and x 3 are disease severity at age 40-70, , and >100, respectively. The estimated losses in yield associated with progress curves were calculated, and the results in Fig. 40. Difference between estimated loss and actual loss was less than 5%. The equation predicts no loss at 0 % disease because there is no intercept. 3. Area under the Curve (AUDC) or Integral Model Correlation between yield and AUDC in this study was highly significant (R 2 = 0.96). Regression between yield y (10 3 kg/feddan) and AUDC (proportion-day) resulted in the following relationship: y= * AUDC R 2 = where y is predicted tuber yield loss and AUDC is the area under disease progress curve. As mentioned above for multiple-point a difference between estimated loss and actual loss was less than 5%. The equation predicts no loss at 0 % disease because there is no intercept.

5 Disease Disease severity and percentage of loss yield in different locations during winter seasons Regions Growing seasons a Disease severity Days after planting >100 otato yield (Ton/feddan)* roductivity Estimated Yield loss% b Badrashin Kom Hamada Kafr El-Zayat Bosaily Badr Salhia Meet Ghamer '-' indicator sign for unsurveied seasons. a assessment keys, which described by Clive James (1947). b yield lose % is (100 ((normal yield productivity / estimating yield)*100)). * Data of yield and productivity obtained from FAO HStatistical DatabasesH Report

6 (A) % Yield loss (B) AUDC % Actual redicted (A) Fitting between estimated (redicted Y) and actual (Y) yield % loss using data analysis by liner regression. (B) AUDC related yield loss to disease severity at the growing season of potato during winter season