Epidemiology of potato late blight disease and other major postharvest biotic stressesin Malawi

The epidemiology of Potato Foliar Late Blight (PFLB) disease (Phytophthora infestans) was quantified in major potato production areas of Malawi. Seed multiplication fields, tests clones and local farmers’ fields were sampled basing on Area Under Disease Progress Curve (AUDPC). The determined severity values were transformed into AUDPC coefficients 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 significant statistical differences in PLB disease across seed multiplication fields, test clones and local farmers’ fields. AUDPC values differed significantly (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 (coefficients, 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 significant differences 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 influenced by the district where the tubers were sampled (x2= 9.26, p-value < 0.001) while the type of variety sampled did not have any significant difference on PBW (x2= 3.59, p-value = 0.268). The presence of potato tuber moth which varied among the sampled districts, was not influenced by variety sampled. The paper has documented and quantified increasing epidemic spread of late blight disease and the consequent effect on sustainable potato production and clean seed systems in Malawi.