Submit Manuscript | http://medcraveonline.com Introduction Potato (Solanum tuberosum L.) is the third most consumed crops, after wheat and rice world-wide. 1 . However, potato plants are susceptible to many pests and pathogens that seriously limit its production. Potato late blight, caused by the oomycete Phytophthora infestans, is one of the main diseases in potato production. 2,3 Phytophthora in Greek means ‘plant destroyer’ which is an apt name for this aggressive pathogen. A historical catastrophe that shows the devastating efects of this disease occurred in Europe in the mid- nineteenth century, 4,5 Potatoes originated in South-America and were introduced to Europe in the 16th century, without late blight. Since then potato had become the most important crop in Europe, still free of late blight. 4 Around 1845 a strain of P. infestans arrived in Europe, which resulted in severe late blight outbreak, especially in Ireland, where about a third of the population relied on the crop for food, and the impact was severe. The late blight epidemic led to the ‘Irish potato famine’ during which one million people died because of starvation and another million emigrated to Britain, the U.S. and Canada. 5,6 Potato late blight disease causes annual losses of several billion dollars and it is a global threat for potato growers. 7 The pathogen originated from Central Mexico. 8 In the middle of the 19th century the pathogen was introduced into the US and Europe, 7 Phytophthora infestans is a hemi-biotrophic flamentous fungus-like heterothallic oomycete that attacks living parts of plants from the family Solanaceae. The pathogen causes lesions with necrotic cells in the middle, surrounded by a ring of gradually necrotizing tissue. Once infected, plants initially appear healthy, before necrotic lesions develop. Under favorable weather conditions, the pathogen can destroy potato foliage in 10 to 15 days and potential yield can be reduced by 50 to 70%. 7 The Department of Agricultural Research Services (DARS) and the International Potato Centre (CIP) in Malawi have introduced population B3-clones as a way of fghting the disease in Malawi. Population B3 is the most advanced source of horizontal resistance available at CIP to deal with the potato late blight disease other than the transgenic lines. In this population, testing and selection is for horizontal resistance to late blight, 9,10 unlike those previously applied to population A clones, which had a focus on dominant R-genes. Despite these eforts high incidences of late blight continue to be observed. Studies have shown that LB incidences has been ranging from 15% to 25% in Dedza and Ntcheu in on-station evaluation sites. 11 However, there has been no documented survey covering the magnitude of the problem in farmers’ felds other than work done in experimental trials. Disease severity in a plant-pathosystem can be assessed either at the peak of the epidemic or several times at some intervals starting from disease initiation until the end of the epidemic. The former method of assessment measures the cumulative efects of all the factors operating during the course of epidemic viz. the terminal disease severity scores (TDS), while the latter can be used to estimate diferent parameters like the area under the disease progress curves (AUDPC), relative area under the disease progress curve (RAUDPC), logistic and Gompertz apparent infection rates, the time required MOJ Food Process Technols. 2021;9(2):80‒86. 80 ©2021 Mbewe et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially. Epidemiology of potato late blight disease and other major postharvest biotic stresses in Malawi Volume 9 Issue 2 - 2021 Willard K Mbewe, 1 Obed J Mwenye, 2 Ellen Gondwe, 3 Antony Nyirenda, 4 Gloria Supa, 1 Kennedy Masamba, 1 Stanley P Kwendani, 1 Margaret Chiipanthenga, 1 Felistus P Chipungu 2 1 Department of Agricultural Research Services, Bvumbwe Agricultural Research Station, Malawi 2 International Potato Centre, Malawi 3 University of Malawi, Chancellor College, Mathematical Sciences Department, Malawi 4 Department of Agricultural Research Services, Malawi Correspondence: Willard K Mbewe, Department of Agricultural Research Services, Bvumbwe Agricultural Research Station, P. O. Box 5748, Limbe, Malawi, Tel +265997930099, Email Received: September 03, 2021 | Published: September 15, 2021 Abstract The epidemiology of Potato Foliar Late Blight (PFLB) disease (Phytophthora infestans) was quantifed in major potato production areas of Malawi. Seed multiplication felds, tests clones and local farmers’ felds were sampled basing on Area Under Disease Progress Curve (AUDPC). The determined severity values were transformed into AUDPC coefcients characterizing rate of disease spreading across the crop. Results indicate minimum and maximum AUDPC values of 0 and 1050 respectively, with an average value of 233.57. The results show signifcant statistical diferences in PLB disease across seed multiplication felds, test clones and local farmers’ felds. AUDPC values difered signifcantly (p < 0.001) among potato growing districts, as well as sources of seed (aeroponics, sandponics, and vendors). Post-harvest survey targeting potato tubers showed that tubers that were sampled from Mzimba district had the highest likelihood of being infected with Potato Tuber Late Blight (PTLB), followed by potatoes that were sampled from Lilongwe (coefcients, b= 1.89, t = 6.11, p-value<0.001) while the potatoes tubers that were sampled from Ntcheu did not vary in the severity with those that were sampled in Dedza. Susceptibility to potato PTLB among potato varieties were varied, with Rosita likelihood to PTLB disease, while there were no other signifcant diferences to PTLB in the rest varieties (b=1.12, t=4.23, p-value<0.001). An extended study on bacterial wilt (PBW) revealed that disease was infuenced by the district where the tubers were sampled (x 2 = 9.26, p-value < 0.001) while the type of variety sampled did not have any signifcant diference on PBW (x 2 = 3.59, p-value = 0.268). The presence of potato tuber moth which varied among the sampled districts, was not infuenced by variety sampled. The paper has documented and quantifed increasing epidemic spread of late blight disease and the consequent efect on sustainable potato production and clean seed systems in Malawi. Keywords: epidemiology, area under disease progress curve, disease management, potato, Malawi MOJ Food Processing & Technology Research Article Open Access