Effect of maize and gibberellic acid on sunflower broomrape germination, control and growth in sunflower field

Sunflower broomrape (Orobanche cumana Wallr.) is a parasitic, herbaceous root plant that has severe effect on industrial crops like sunflower. In order to reduce the parasitic effect of sunflower broomrape on sunflower and sunflower broomrape seed bank, two generalized maize varieties ('Jingnuo No. 1', 'Xinyu No. 57') in Xinjiang Uygur Autonomous Region of China were used in a plug tray experiment to study the effects of application of two exogenous concentrations of gibberellin acid (10^-4 mol·L^-1 and 10^-5 mol·L^-1) at different periods (10 d and 15 d after germination) on maize growth and development, and secretion of stimulant of sunflower broomrape seed germination. The study screened out more capable maize variety for pot experiment by collecting and extracting root exudates of maize to stimulate sunflower broomrape seed germination after 24 days. Through applying GA₃(10^-4 mol·L^-1) at different times after planting, the study also explored the combined effects of maize and GA₃ on controlling sunflower broomrape seeds. Thus in the pot experiment, GA₃ was exogenously applied 20 and 40 days after planting maize, and plant samples (leaves, stems and roots) and rhizosphere soils collected at harvest (105 d) were used to further analyze sunflower broomrape seed germination. Sunflowers were planted in pots that were planted with maize in the past years. The epigaeous number of sunflower broomrape was counted and sunflower plants of agronomic index measured at harvest. The results showed the application of GA₃ in the plug tray experiment had a significant effect on maize height. In addition, there was no inhibiting effect on maize in terms of secreting germination stimulant of sunflower broomrape. Thus, it was productive to apply GA₃(10^-4 mol·L^-1 and 10^-5 mol·L^-1) during maize growth period. Moreover, 100-dilution of root exudate of 'Xinyu No. 57' maize variety showed more significantly stimulating effect on sunflower broomrape germination rate than 'Jingnuo No. 1', 'Xinyu No. 57' was finally used in the pot experiment. In the pot experiment, maize heights under 10^-4 mol·L^-1 GA₃ application after 20 and 40 days of maize planting were higher than that under the control (no application of GA₃), with respective increases of 22.5% and 19.1%. Sunflower was planted in the second year after maize, which was treated by GA₃at 20 days after planting. The diameter of sunflower disk increased by 57.1% compared with the control. Compared with control, the number of epigaeous sunflower broomrape was 1.3·plot^-1 and 1.8·plot^-1, which suggested decreases of 76.4% and 67.3%, respectively. In conclusion, the application of 10^-4 mol·L^-1 GA₃ to maize after 20 and 40 days of planting stopped sunflower broomrape seed germination and thereby reduced sunflower broomrape damage to sunflower.