Sweetpotato stem rot nematode (Ditylenchus destructor) causes the most devastating disease affecting sweetpotato production in China. The objectives of this study were to (i) establish a quantification method using real-time PCR for D. destructor of sweetpotato; (ii) analyze the effect of D. destructor density at harvest on the percentage of disease incidence in sweetpotatoes; and (iii) evaluate the effect of soil physical properties on disease incidence. Populations of D. destructor isolated from 28 different production areas in Henan Province exhibited identical sequences, and then real-time PCR-specific primers (PRNf and PRNr) were designed. The primer set demonstrated a 100% match with the sequences of D. destructor from three regions in China but did not align perfectly with different species within the genus Ditylenchus isolated from nine other countries. There were two and thirteen base mismatches with the closely related species D. africanus and D. gallaeformans, respectively. The log-transformed number of inoculated nematodes (x) to soil was highly correlated with the corresponding Ct value (y), resulting in the quantification curve (y = −1.0859x + 32.025, R² = 0.9866, P < 0.01). This quantification curve was utilized to evaluate the densities of D. destructor in wheat fields that were not cultivated with sweetpotato and in fields under continuous sweetpotato cultivation. The results showed no detection in the wheat fields, and the densities ranged from 0 to 13,300 ± 1,020 individuals per 20 g of dry soil. At harvest, the D. destructor density established a negative correlation with soil pH (y = −1.7431x + 12.568, R² = 0.6028, P < 0.05). When soil pH values were between 5.6 and 6.8, and the density of D. destructor at harvest was less than 160 ± 30 per 20 g of soil, the percentage of disease incidence at harvest was 0. A significant correlation was established between D. destructor density and the severity of sweetpotato disease. The results indicate that the specific primer set developed in this study allows for the accurate and rapid quantification of D. destructor density in the soil, as well as the prediction of disease incidence in sweetpotato.

Tobacco Fusarium root rot, caused mainly by Fusarium oxysporum and F. solani, poses a major threat to tobacco production by severely impairing root function and reducing yield and quality. In the context of sustainable agriculture, biological control has gained increasing attention as an environmentally friendly and effective alternative to chemical pesticides. This study evaluated four tobacco rhizosphere Bacillus strains to clarify how key biological traits relate to field performance in controlling Fusarium root rot. Strains were assessed for antifungal activity, indole-3-acetic acid (IAA) production, chemotaxis toward root exudates, biofilm formation, and colonization capacity. Significant differences were observed, with G12 and G51 exhibiting the most favorable profiles. Both showed strong antifungal activity (42.42%-57.50%), robust chemotaxis toward root exudates from healthy tobacco plants (RCI up to 35.86), efficient biofilm formation, and successful colonization of tobacco tissues. Greenhouse assays demonstrated that G12 and G51 reduced disease indices to below 10.00 and achieved control efficacy above 90%, approaching that of chemical treatment. Multi-location field trials in 2024-2025 further confirmed their effectiveness, with both strains reducing disease incidence by more than 60% and consistently improving agronomic traits. G51 provided the most stable yield benefits across years and sites, while G12 and G51 also accelerated the decline of chlorophyll and leaf nitrogen content at later stages, suggesting a role in promoting earlier maturation. Overall, this study establishes a link between chemotaxis, biofilm formation, colonization, and field efficacy, underscoring the importance of integrating multiple biological traits when screening biocontrol agents. These findings provide scientific support for the application of tobacco rhizosphere Bacillus strains in the sustainable management of Fusarium root rot.

Introduction: Unmanned aerial vehicles (UAVs) have rapidly developed as efficient plant protection machinery and are widely used for pesticide application across complex terrains. However, optimal operating parameters for UAV spraying in tobacco fields remain insufficiently defined across different growth stages. Methods: This study assessed the spraying performance of two UAV models, T20P and T40, under multiple combinations of flight height, flight speed, and spray volume. Experiments were conducted during the rosette stage, vigorous growth stage, and maturity stage of tobacco plants. Using a multi-index weighted analysis method, the optimal combinations of operational parameters for different tobacco growth stages were evaluated. Results and Discussion: The results indicated that variations in operational parameters significantly affected the deposition and distribution of droplets. For T20P, the optimal parameters for the rosette stage were a flight speed of 3 m•s ^-1 , a flight height of 2 m, and a spray volume of 50 L•ha ^-1 . During the vigorous growth stage, the optimal parameters were a flight height of 2.5 m, a flight speed of 4 m•s ^-1 , and a spray volume of 50 L•ha ^-1 . For the maturity stage, the parameters were a flight height of 2.5 m, a flight speed of 3 m•s-1, and a spray volume of 50 L•ha ^-1 . For T40, the optimal parameters for the rosette stage were a flight height of 3 m, a flight speed of 3 m•s ^-1 , and a spray volume of 50 L•ha ^-1 . During the vigorous growth stage, the parameters were a flight height of 3.5 m, a flight speed of 4 m•s ^-1 , and a spray volume of 50 L•ha ^-1 . For the maturity stage, the parameters were a flight height of 3.5 m, a flight speed of 3 m•s-¹, and a spray volume of 50 L•ha ^-1 . By applying these optimized parameters at the corresponding growth stages, a balanced spray performance can be achieved, thereby maximizing pesticide utilization. These findings provide a practical reference for improving droplet deposition and enhancing the effectiveness of UAV pesticide application in tobacco production.