Silicon Fertilization Improves Sunflower Rhizosphere Microbial Community Structure and Reduces Parasitism by <i>Orobanche cumana</i> Wallr.

Sunflower broomrape (<i>Orobanche cumana</i> Wallr.) has severely restricted the development of the sunflower industry in China, and more efficient and convenient control methods are urgently needed. In this experiment, we investigated the effects of N, P and silica fertilizers on the parasitism rate of <i>O. cumana</i>, as well as on the yield of sunflower and native microbial communities in the field. Firstly, pot experiments were conducted to select the most effective fertilization method and to determine the physiological and biochemical indexes of sunflowers. Subsequently, field application studies were carried out to determine the physiological indexes, yield, <i>O. cumana</i> parasitism on sunflower, and the effect on the indigenous microbial community. The results demonstrate that compared with the CNP treatment (Control), the number of parasites under the N1P5 treatment significantly decreased by 66.15%. The exogenous application of silica can significantly reduce the number of <i>O. cumana</i> parasites. The treatments with N1P5 (N/P = 1:5) and available SiO₂ content higher than 40 mg/kg (NS2, NS3, SF2 and SF3) significantly increased superoxide dismutase (SOD) activity and decreased malondialdehyde (MDA) content in sunflower leaves. In the field, fertilization significantly decreased the number of <i>O. cumana</i> parasites. The S treatment improved the native microbial community structure and enriched beneficial microorganisms, including Vicinamibacteria and Pyrinomonadaceae. Additionally, applying the S treatment significantly increased sunflower yield by 23.82% and crude protein content by 20.20%. In summary, the application of silicon fertilizer can effectively improve the host microbial community, reduce <i>O. cumana</i> parasitism and improve the yield and quality of sunflower.