Biocontrol of <i>Mycosphaerella fijiensis</i> Morelet, the Causal Agent of Black Sigatoka of Banana Tree (<i>Musa</i> spp.) Using Biopesticides in Côte d’Ivoire

Abstract

Black Leaf Streak Disease (BLSD) is the most restricting leaf disease to banana tree cultivation around the world. In order to control this disease, synthetic fungicides are extensively used. However, these products pose a real danger to environmental pollution and the health of applicators and consumers. Faced with this situation, alternative solutions must be considered to overcome their systematic use. This study was initiated in this context so as to assess the effectiveness of 20 biopesticide formulations on <i>Mycosphaerella fijiensis</i> conidia stemming from banana tree leaf samples originating from village plantations and showing the typical symptoms of stage 2 or 3 black Sigatoka. The assessment method used was that of dispersion in solid medium. Observations were made under an optical microscope equipped with a camera and consisted in determining the inhibition rates of conidia germ tube growth. A pathogenicity test was performed with 8 <i>Mycosphaerella</i> spp. isolates according to an inoculation technique under controlled conditions on whole plants of 5 banana tree cultivar vivoplants. The assessment of biopesticide protection effectiveness against BLSD was conducted on cultivar "Orishele" (very susceptible) with the most aggressive and virulent strain selected during isolate pathogenicity test. The results obtained show that all biopesticide formulations have significant antifungal activity on <i>M. fijiensis</i> conidia germ tube elongation. The average inhibition rate ranged from 83.31 to 99.89% for all biopesticides. The 8 <i>M. fijiensis</i> isolates used have all raised symptoms characteristic of black leaf streak disease regardless of the cultivar. In contrast, no isolate caused symptoms characteristic of Sigatoka disease (Yellow Sigatoka). Biopesticides and synthetic fungicides significantly reduced disease development rate compared to inoculated and untreated controls, but at varying degrees. Preventive treatment of seedlings is found to be much more effective than curative treatment. However, in order to protect banana and plantain tree varieties against <i>M. fijiensis</i>, both types of treatments are necessary.