Identification and Biological Control of Fungal Pathogens Associated with Cactus Pear Diseases in Morocco

The cactus pear (Opuntia spp.) is a crop of major economic and ecological importance in arid and semi-arid regions. However, with its domestication and intensification, symptoms of fungal diseases have begun to emerge in different cultivation areas. This study was conducted to identify the pathogenic fungi associated with symptoms observed on cladodes in different regions of Morocco and to evaluate the effectiveness of bacterial and fungal antagonists. The study enabled the isolation and identification of several fungal agents from symptomatic cladodes, namely Alternaria alternata, Alternaria tenuissima, Colletotrichum gloeosporioides, and Aspergillus tubingensis. Among these pathogens, A. alternata proved to be the most aggressive and was therefore selected for in vitro and in vivo antagonism assays. Twelve bacterial isolates belonging to the genera Bacillus and Pseudomonas, as well as one isolate of Trichoderma harzianum, were evaluated for their antifungal activity. All antagonists showed significant inhibitory effects against A. alternata in vitro preliminary assay. However, the bacterial isolates B. siamensis, B. halotolerans, and P. peli, as well as T. harzianum, exhibited the highest efficacy. This efficacy was confirmed through direct confrontation tests in vivo on one-year-old cladodes for the three bacterial isolates. In contrast, T. harzianum showed significant pathogenic potential on cladodes of O. ficus-indica and O. megacantha. Investigation of the mechanisms of action of the three most effective bacterial isolates revealed their ability to produce antifungal volatile organic compounds. Enzymatic analyses showed differential production of amylase, chitinase, cellulase and protease among the three isolates, while genes associated with the biosynthesis of antifungal lipopeptides were detected only in P. peli.