MORPHOLOGICAL VARIABILITY WITHIN POPULATIONS OF ALTERNARIA PORRI (ELLIS) CIF., THE CAUSATIVE AGENT OF ONION PURPLE BLOTCH DISEASE IN BURKINA FASO

Onion production in Burkina Faso remains limited due to certain devastating diseases such as purple blotch caused by Alternaria porri.This disease causes significant yield losses and is difficult to control with chemicals.This difficulty could be linked to genetic, pathogenic and/or pathogenicvariability within populations of A. porri.The objective of the present study was to evaluate the morphological variability of Alternaria porri populations occuring in Burkina Faso with a view to better define appropriate methods in controlling the disease. Thus, fiftyisolates of A. porri, obtained from diseased onion leaves collected in the different agroclimatic zones, were morphologically characterized.Multivariate analyses were carried out on the data collected using XLSTAT 2016.7.02 software. These analyses revealed variability of A. porri in its morphological aspects such as colony color, radial growth and micropropagules production.All of the characterized isolates were grouped into three classes. Class 1 with 34 individuals, characterized by weak radial growth but high production of micro propagules. The second class composed of four isolates, is characterized by individuals with strong mycelial growth and a low capacity for the production of micro propagules.A third class, composed of twelve isolates, is characterized by intermediate individuals in terms of growth and production of micro propagules.However, this clustering into classes did not align with the geographic origin of the isolates. A pathogenicity study should be carried out with representatives of the three classes in order to understand whether this observed morphological variability is linked to the virulence of the fungus.