Defense Mechanisms of Sweet Potato Varieties (<i>Ipomoea batatas</i> L. [Lam]) Enhanced by Neem Seed Extract Against Root-knot Nematodes and <i>Fusarium</i> Wilt

Sweet potato crops are severely threatened by nematodes of the genus <i>Meloidogyne </i>spp. and <i>Fusarium </i>sp. fungi, which are responsible for <i>Fusarium</i> wilt. Nematodes cause root and tuber deformities, as well as wilting of stems and leaves, while <i>Fusarium</i> wilt leads to rot, necrosis, and wilting. These two pests contribute to a significant reduction in yields and substantial losses of production. Control measures primarily rely on the use of chemicals, whose excessive use poses a threat to the environment and human health. This study aims to assess the tolerance of four sweet potato varieties treated with aqueous neem seed extract against combined attacks from nematodes and <i>Fusarium spp</i>. A completely randomized block design with four sweet potato varieties (V1: white variety from the center region (togologo); V2: white variety from Adamawa region (lambadidi); V3: Improved Yellow variety (IRAD 1112); V4: Yellow variety from the center region (Bété)) and four treatments (T0: non-inoculated varieties; T1: varieties inoculated with nematodes + <i>Fusarium</i>; T2: varieties inoculated with nematodes + <i>Fusarium</i> then treated with neem aqueous extract; T3: varieties inoculated with nematodes + <i>Fusarium</i> then treated with synthetic pesticides) was used in a greenhouse. Agro-morphological, epidemiological parameters, and biochemical resistance markers were evaluated. The results revealed that treatment with neem extract (T2) reduced severity rates by 60 to 80% in the different growing bags compared to treatment (T0), followed by treatment (T3). The highest yields were obtained in treatments T1 and T2 across all varieties. The Adamawa White variety (lambadidi) (V2) and the IRAD 1112 variety (V3) exhibited the highest yields with up to 7 t/ha in T3 treatment. The content of phenolic compounds, proteins, and the enzymatic activity of peroxidase were higher in sweet potato plants inoculated with <i>Fusarium</i> and treated with neem aqueous extract. Neem treatment showed strong protective potential in combating fungal diseases and nematodes affecting sweet potato.