Effects Of Several Crops,Weeds And Their Straws On Seed Longevity Of Phalaris Minor

Phalaris minor is a common weed in wheat fields.It closely resembles wheat in its morphological characteristics and is difficult to control.Overseas,P.minor has developed a certain degree of herbicide resistance during weed control processes.To avoid the emergence of herbicide resistance in P.minor during its control in China,there is a need to explore an ecological control method that affects the seed longevity of P.minor,thereby reducing the soil seed bank of this weed.This is a requirement for the development of modern agriculture.In this study,a pot experiment was conducted to investigate the control of P.minor seed longevity in two stages: seed dormancy and germination.Fifteen summer crops,nine summer weeds,and eight winter crops were planted individually.Additionally,seven types of summer crop straw were used for cover or mixed cultivation,along with four types of winter crop/weed straw.The crops,weeds,and straw that could control the seed longevity of P.minor were selected.The root exudates of these selected plants were collected and tested through sand culture experiments to examine their effects on seed germination and seedling growth of P.minor.The plant root exudates were extracted using a solvent extraction method,yielding three extract fractions: water phase,dichloromethane phase,and ethyl acetate phase.The impact of these extract fractions on P.minor seed germination was determined.LC-MS analysis was employed to identify the highly active chemical components in the water phase and screen for major secondary metabolites and their allelopathic activities.This study aims to provide a theoretical basis for the development of a rational crop rotation system to reduce the damage caused by P.minor.The results of the research are as follows:(1)In the 2021 experiment,the seed emergence rates of P.minor were 22.0% to27.0% for tomato,chili pepper,corn,soybean,cabbage,and potato,which were higher than the control group(15.5%).The results of the 2022 experiment were consistent with those of 2021.The seed emergence rates of P.minor were 44.0% to76.0% for tomato,chili pepper,corn,soybean,cabbage,and potato,higher than the control group(38.0%).Planting these crops can reduce the number of P.minor seeds in the soil seed bank,but almost all ungerminated seeds remain viable.The decay rate of P.minor seeds during the planting period was only 1% and 4%.Planting sorghum and rice can suppress the emergence of P.minor.Summer cover with P.minor straw and wheat straw can promote the emergence of P.minor seeds.However,when covered with rapeseed and fava bean straw,the seed emergence rate of P.minor was50%,showing inhibitory effects compared to the control group(64.5%).During winter,the application of chili pepper straw in the soil effectively suppressed the emergence of P.minor seeds,and planting peas and shepherd’s purse showed inhibitory effects on P.minor emergence.(2)Through the collection of root exudates from plants during the growing season,sand culture experiments were conducted in the laboratory to examine the inhibitory effects of sorghum and rice root exudates on P.minor seed germination.Sorghum,rice,and cabbage showed a certain degree of inhibition on the seedling growth of P.minor.The root exudates of rice and eggplant exhibited some inhibition on the root elongation of P.minor.The root exudates of tomato,corn,and cabbage had a promoting effect on the germination of P.minor.The root exudates of chili pepper,tomato,potato,corn,and soybean promoted the seedling growth of P.minor,but the promoting effect of corn was relatively weak.The root exudates of cabbage and potato had a certain promoting effect on root elongation.(3)Root exudates were obtained through hydroponic cultivation of sorghum,rice,hollow-root sedge,foxtail grass,shepherd’s purse,peas,tomato,potato,and cabbage.Water extracts were obtained from fava bean,rapeseed,and chili pepper straw,using organic solvents ethyl acetate and dichloromethane for extraction.The effects of different extracts on P.minor seed germination were evaluated,with the inhibitory effect of solvent extraction ranking as water extract > ethyl acetate >dichloromethane.The water extract of rice exhibited inhibition rates ranging from3.58% to 13.22%,showing stronger inhibitory effects compared to other crops.The water extract of tomato demonstrated inhibition rates ranging from-94.14% to-96.83%,indicating a promoting effect on germination,which was stronger than that of cabbage and potato.The water extract of chili pepper straw exhibited inhibition rates ranging from 63.36% to 100%,showing stronger inhibitory effects than fava bean and rapeseed straw.(4)LC-MS analysis was conducted to identify the relative content of major chemical components in the root exudates of sorghum,rice,shepherd’s purse,and tomato,as well as the water extract of chili pepper straw.A total of 839 compounds were detected,including 28 phenolic compounds and their derivatives,35 phenolic acids,86 flavonoids,27 alkaloids and their derivatives,and 29 terpenes.