Effectiveness Of Broomrape Management Using Maize And Foxtail Millet As Trap Crops

Broomrape(Orobanche spp.and Phelipanche spp.)is a genus of root parasitic herbaceous plant,parasitizing economic crops such as sunflower,tomato,tobacco,resulting in substantial losses in agricultural production.In China,the most widely distributed weedy broomrapes are sunflower broomrape(Orobanche cumana Wallr.)and Egyptian broomrape [Phelipanche aegyptiaca Pers.(syn.O.aegyptiaca)].Management strategies have been largely unsuccessful mainly because of the complex life cycle of broomrape.The use of false hosts(trap crops),which offer the advantage of stimulating broomrape germination without being parasitized can be effective to some extent in reducing broomrape seed bank and controlling broomrape.This study,proceeding from(1)analyzing the effect of conditioning on broomrape seeds sensitivity to various germination simulants,(2)assaying the ability of foxtail millet(Setaria italica L.)and maize(Zea mays L.)under various cultivars and environment to stimulate broomrape seeds germination,(3)the actual effectiveness of cereals rotation on broomrape management to ultimately analyze and evaluate the effectiveness of foxtail millet and maize as trap crops for controlling broomrape from both receptor and donor respects.The main conclusions of our study were showed below:1.Conditioning agents and period significantly influenced the sensitivity of sunflower broomrape and Egyptian broomrape seeds to various germination stimulants.The dormancy of broomrape seeds is released during preconditioning and that seeds,therefore,begin to be sensitive to germination stimulants.Prolonged conditioning resulted in wet dormancy and a reduction in germination(11-20%).A cubic curve model provided a good fit for the germination of the broomrape seeds and conditioning period.In addition to that,the germination rates of sunflower conditioning for 1 and 21 days were 45 and 50% which were significantly higher than that conditioning with distilled water(21 and 18%).The application of GA3 shortened the conditioning period requirement of broomrape seeds and prevented the seeds from entering a stage of wet dormancy.The germination of sunflower broomrape responded to strigol(62.8%)> maize root exudates(58.2%)> GR24(57.9%)> tobacco root exudates(41.6%)> DCL(41.3%).The stimulants that induced Egyptian broomrape germination were ranked in decreasing order as GR24(76.8%),strigol(76.1%),tobacco root exudates(49.5%),dehydrocostus lactones(DCL,39.2%),and maize root exudates(18%).The germination rate of the broomrape seeds reached a maximum under a conditioning period of 4–10 days2.Rhizosphere soil from foxtail millet induced sunflower broomrape seed germination directly.However,foxtail millet didn’t have the ability to induce Egyptian broomrape germination.The germination inducing activity of various millet cultivars was: Hong Guzi(30%)> Cao Guzi and Jingu 21(23 and 20% respectively)> other cultivars(14-17%).Hong Guzi grown in a 1:1 sand/soil ratio induced the highest germination of sunflower broomrape(30.1%).Nitrogen greatly suppressed the germination inducing capacity of foxtail millet.Rotation of appropriate foxtail millet cultivar(Cao Guzi and Jingu 21)reduced the number of sunflower broomrape attachments(50–80%).3.Maize cultivars(108 cultivars)were assayed for their ability to stimulate germination of broomrape seeds.The maize cultivars screened out to have higher ability of inducing sunflower broomrape seeds germination(>40%)were: Xianzhengda 408,Zhengdan 958,Wugu 568,Xianyu 252,Dafeng 30 and Neidan 314.The maize cultivars screened out to have higher ability of inducing Egyptian broomrape seeds germination(>60%)were jinong 107,Daoyuan 8,Fengtian 6,Longyuan 3,Jinongdaqingsi 1,Tiexu 1843 and Zhengdan 958.In addition to that,the broomrape germination inducing ability of maize cultivars under various experiments was significantly correlated which provide the possibility of using leaf extracts as rapid detection technology to assay the broomrape germination inducing capacity of maize.4.Salt and nutrition stress strongly increased the inducing activities of maize root and rhizosphere soil extracts on broomrape germination.The root extracts of maize under salt stress induced higher germination of sunflower broomrape(55%)and Egyptian broomrape(34%)compared with control(48 and 32%).Phosphorus exhibited the largest effect on broomrape germination inducing capacity of maize.Compared with the treatment of applying 750 mg kg-1 phosphorus,the germination rate of broomrape induced by maize grown in soil without phosphorus fertilizer application was 5-20% higher.Under salt and nutrient stress,abscisic acid(ABA)of maize was accumulated in apical parts of the maize roots and the contents of ABA was significant positive correlated with the broomrape germination inducing ability of maize.5.Rotation of maize reduced broomrape infestation on subsequent host and increased host biomass.The effectiveness of broomrape management among various maize cultivars was significantly different.However,the differences among various maize cultivars was decreased with the years of maize cultivated prolonged.After cultivated Neidan 314 for 3 years,sunflower broomrape attachment was the lowest(0.8 attachment plant-1)which was 3% compared to the control,the sunflower shoot dry mass(29 g)was 200% higher compared with control and similar to sunflower grown without broomrape(30 g).After Qingzhu 67,Neidan 314 and Haoyu 19 cultivated for 3 years,there was no Egyptian broomrape attachment on subsequent tomato and shoot dry mass of tomato(25 g)was significantly promoted which was 8 times control(3 g)and formed a homogeneous group with tomato grown without broomrape(26 g).The correlation analysis between the growth parameters of subsequent hosts and broomrape infestation levels showed that reduction of broomrape attachment has contributed to the increasing biomass of sunflower and tomato.In conclusion,this study proposed that maize can be used as trap crop for sunflower broomrape and Egyptian broomrape management.Neidan 314 had the strongest stimulation effect on sunflower broomrape,while Zhengdan 958 had the strongest stimulation effect on Egyptian broomrape.Foxtail millet didn’t have the ability to induce Egyptian broomrape germination,but could be used as trap crop of sunflower broomrape.Environment factors significantly influenced the effectiveness of these two cereals being used to control broomrape.Thus,the use of foxtail millet and maize as trap crops can be effective to reduce the broomrape attachment,increase host biomass and reduce the contamination of pesticide to the environment.These results will be of value for developing new synthetic broomrape management strategies.