Potentiel bioactif des extraits des graines de Jatropha curcas L. contre la fusariose, la sclérotiniose et quelques insectes ravageurs du niébé (Vigna unguiculata L. Walp)

Abstract

Cowpea (Vigna unguiculata L. Walp.), a legume native to Africa, is widely cultivated in arid and semi-arid regions. In these areas, fusarium wilt caused by Fusarium oxysporum f.sp. . tracheiphilum, white mold due to Sclerotinia sclerotiorum, and insect pests are the main biotic threats, leading to crop losses ranging from 50 % to 100 %. The intensive use of chemical pesticides to combat these issues raises serious environmental and health concerns. In this context, the present study aims to control these attacks using seed extracts from Jatropha curcas. A GC-MS analysis was performed on aqueous, acetone, and hexane extracts from J. curcas seeds. These extracts were then tested in vitro in triplicate at concentrations of 15, 30, 60, and 120 μL/mL, and compared to a synthetic fungicide containing 80 g/kg of Metalaxyl and 640 g/kg of Mancozeb as active ingredients. The seed extracts were also evaluated under field conditions on two cowpea varieties (improved and local) using a split-plot design with four replications and six different treatments. Their effects were assessed on disease severity, insect damage, and yield. Additionally, the biochemical compounds and the activity of several oxidative enzymes were measured in the treated cowpea leaves. The GC MS analysis of J. curcas seed extracts revealed the presence of several secondary metabolites known for their biopesticide activity. In vitro tests showed complete inhibition of mycelial growth of F. oxysporum and S. sclerotiorum with aqueous and acetone extracts at concentrations of 60 and 120 µL/mL, comparable to the synthetic fungicide. The aqueous extract stood out with lower minimum inhibitory concentrations (MIC50) and strong effectiveness against spore germination. In field trials, the seed extracts significantly reduced disease incidence and severity, as well as insect damage, leading to improved crop yield. For the improved variety Lori 24-130, the highest yield was obtained with the synthetic fungicide (1080 kg/ha), closely followed by the aqueous extract (1035 kg/ha), while untreated plots recorded the lowest yields (630 kg/ha). For the local variety, the aqueous extract resulted in the highest yield (885 kg/ha), followed by the synthetic fungicide (882.98 kg/ha), with significantly lower yields in the control plots (330 kg/ha). J. curcas seed extracts significantly improved cowpea yield by stimulating the production of biochemical compounds and oxidative enzymes essential for plant development.