The potential of foxtail millet as a trap crop for sunflower broomrape

Heavy infestation of large areas in China by the root parasitic sunflower broomrape (Orobanche cumana Wallr.) constitutes a major threat to sunflower production. This study was conducted to investigate the potential of foxtail millet as a trap crop for the management of sunflower broomrape (SB). To assay the ability of foxtail millet to stimulate germination of SB seeds, the rhizosphere soil of six foxtail millet cultivars cultured in various sand/soil ratios and fertilizer levels were employed to directly induce SB germination. Among all sand/soil treatments, Hong Guzi grown in a 1:1 sand/soil ratio induced the highest germination of SB (30.1%). Phosphorus resulted in a small but significantly higher germination of SB compared with the control without any fertilizer, while in contrast, nitrogen greatly suppressed the germination inducing capacity of foxtail millet even at concentrations as low as 28 mg kg−1 soil (based on N). Cropping rotation experiment was undertaken to quantify the effect of foxtail millet on SB infection in a subsequent sunflower crop. All foxtail millet rotation treatments reduced broomrape infection and gave higher shoot and flower disk dry mass of sunflowers than the control grown without a fore-rotating crop. These results suggest that efficacious cultivars of foxtail millet reduce SB parasitism and increase sunflower yields and that using foxtail millet as trap crop is probably an effective way to reduce the broomrape weed problem in China, especially in the dry, infertile, and sandy soils of the Loess Plateau.