The Effects of Crop Rotation with Chili Peppers and Arbuscular Mycorrhizal Fungi on Root-Knot Nematode Disease in Watermelons

Root-knot nematodes have emerged as one of the most detrimental diseases in continuous cropping of watermelon in protected cultivation. Prolonged reliance on chemical control measures risks soil contamination and heightened nematode resistance. Consequently, there is an urgent need to develop green and sustainable control technologies. Both chili pepper rotation and arbuscular mycorrhizal fungi (AMF) have been proven to suppress root-knot nematodes and promote watermelon growth, but the synergistic mechanisms between them remain unclear. This study employed a greenhouse pot experiment design, planting crops in the soil of continuous cropping watermelon over two seasons. The first season cultivated pepper (Capsicum annuum) and watermelon (Citrullus lanatus) respectively, and the second season uniformly planted watermelon. During the growth of the second season's watermelon, two AMF were inoculated separately: Funneliformis mosseae (Fm) and Glomus versiforme (Gv), to systematically evaluate their combined inoculation effects on the control of root-knot nematode disease and the comprehensive impact on watermelon growth. Results indicate that both pepper rotation and AMF inoculation enhance root vigour, osmotic regulation and antioxidant capacity, thereby improving plant growth and enhancing resistance to Meloidogyne incognita. Among them, the treatment of nematode-resistant pepper rotation combined with Gv inoculation showed the best effect. High-throughput sequencing further demonstrated that this treatment enriched beneficial microbial communities such as Ochrobactrum, upregulated stress-resistant metabolic pathways, and enhanced both rhizosphere microbial stability and systemic resistance. In summary, nematode-resistant pepper rotation combined with Gv inoculation is an effective green control strategy, which can provide a theoretical basis for the sustainable production of watermelon.