Biological And Chemical Responses Of Allelopathic Rice To Neighboring Plants And The Weed-suppressive Mechanisms Of Rice Allelochemical Derivatives

Recognition and response between plant individuals are one of critical topics of research on plant behaviors.In this study,allelopathic rice and non-allelopathic rice were chose as the research objects to investigate the chemical relationship with different coexisting weeds,as well as kin recognition among intraspecific allelopathic rice,especially biochemical plasticity induced by kin recognition of rice when under competition with barnyardgrass(Echinochloa crus-galli)and its possible mechanism.Meanwhile,inhibition effect of rice allelochemical derivative,particularly herbicide resistant Echinochloa crusgalli in paddy field and its mechanism were also researched,in order to utilize interspecific chemical relationships to suppress weeds and improve the production of rice.Results of this research are as follows.(1)When rice coexisted with a single padddy weed,allelopathic rice showed stronger interference effect than non-allelopathic rice and allelopathic rice inhibited growth of paddy weed roots more than shoots regardless of species.When two or three different weeds grew with rice as the neighborat the same time,there was obvious synergistic effect among them,the dicotyledonous weed Eclipta prostrata played a dominant role in the competition.(2)Rice could change the root morphological plasticity of weeds and its distribution,which depended on species of weeds and allelopathic characteristics of rice.Allelopathic rice significantly reduced total root length,total root area,maximum root amplitude and maximum root depth of paddy weeds,while the weeds adjusted horizontal distribution of their roots in response to the presence of allelopathic rice.With the exception of weedy rice,root growth of weeds avoided expanding towards allelopathic rice.Roots of barnyardgrass and weedy rice grew close to the roots of non-allelopathic rice,while C.difformis and E.prostrata avoided them and L.chinensis had no response.(3)Different root segregation between rice and paddy weeds had effects on the interference of allelopathic rice with paddy weeds at the root level.Compared with root contact,root segregated by 30μm nylon mesh significantly increased inhibition of barnyardgrass,E.Prostrata and L.Chinensis through an increase in rice allelochemicals and induction was strongest during 6 h-9 h after addition.In particular,their root exudates induced production of rice allelochemicals.However,similar results were not observed in C.difformis and weedy rice with either root segregation or root exudate application.The inhibition effect was dropped to about 10%when the root was segregated by plastic film.The interference of allelopathic rice with resistant barnyardgrasswas stronger than that on sensitive biotype barnyardgrass,whereas the former showed significantly weaker capacity to induce allelochemicals in allelopathic rice than the latter.(4)Allelopathic rice 6173 had kin recognition capacity.While accompanied by inter-subspecies stranger Liaojing-9 and intra-subspecies stranger 3826,the root biomass was larger than grown with its self or its kin 6368.Root exudates inhibitor and root segregation could lead to disappearance of kin recognition phenomenon.Root exudates of rice what has different genetic relationships with 6173 could also induce its kin recognition.(5)No matter whether there was competition with barnyardgrass,the total root length,lateral root length and total root square of allelopathic rice PI312777 and 6173were lower than grown with strangers when grown with itself and kins.If there was barnyardgrass competition,kin or strangers could resulted in asymmetrical horizontal distribution of the target rice such as PI312777 and 6173.When grown with self and kin species,the concentration of allelochemicals in rice was remarkably lower than with stranger rice variety,but the inhibition effect on barnyardgrassstrengthened remarkably.(6)The rice allelochemical derivative with 4-hydroxyphenyl-pyruvate dioxygenase(HPPD)inhibiting activity was identified as a target compound on photosynthetic performance of herbicide-susceptible versus herbicide-resistant barmyardgrass.Regardless of bamyardgrass biotypes,the benzothiazine derivative greatly affected chlorophyll fluorescence parameters(Fv/Fm,ETR1min and NPQ1min),reduced the chloroplast fluorescence levels,inbibitied expression of HPPD gene,and led the bamyardgrass to albino and even to death.All the activity above make it an ideal lead compound for bleaching herbicide discovery to meeting the challenge of escalating herbicide-resistant weeds.