| Strigolactones(SLs), a new group of plant hormone, are germination stimulants of seeds of Orobanche/Striga spp. and endogenous regulators on plant architectures. Based on the dose-responses of broomrape seeds to SLs, pretreatment conditions of Orobanche seeds were optimized, and the germination responses of seeds of Orobanche cumana to GR24 and root exudates of rice and corn were promoted. By using Orobanche seeds as bio- indicators, we studied the effects of nutrient stresses on the growth of tobacco seedlings and the germination inducing ability of the root extracts and the root exudates of the seedlings on Orobanche seeds, studied the relations between allelopathic potentials and Orobanche seeds germination inducing abilities of rice root exudates, in order to clarify whether there are relations between SLs and plant allelopathy or stress-response. In crop-weed intercultivation experiments, we analyzed the nutrient uptakes and competitive abilities of d27(mutants of SLs synthesis) and WT(wild type) to weedy rice and barnyard grass to clarify the effects of strigolactones on plant allelopathy and the competitions between crop and weeds, and to provide a scientific basis on the function of plant hormone SLs on allelopathy and interspecific competition.The main results obtained in the research are as follows:1. Three on-test species of broomrape(Orobanche minor, O. cumana and Phelipanche aegytiace) seeds exhibited significant difference on the germination dose-responses to levels of GR24. O. minor seeds were sensitive to the conditioning period(C.V = 66.7%), O. cumana seeds were sensitive to the gradient of GR24(C.V = 106.4%). 12-days conditioning was required for O. minor seeds to obtain the maximum germination response to GR24, while O. cumana and P. aegytiace only needed 4-days conditioning. Germination rates increased with days after GR24 applied, reached the maximum at the 8th~10th day. Pretreatment conditions were optimized by using orthogonal experiments and pairwise analysis. Temperature at 38℃, p H 5.2 and sonication for 8 min were finally chose as pretreated condition, as which could induce the highest sensitivity of broomrape to levels of GR24.2. Nutrient stresses(deficiency and salt toxicity) decreased the biomass of on-test tobacco seedlings, but increased germination inducing abilities of their root exudates on broomrape seeds. The biomass of RG declined by 46% and 29% at the nitrogen(N) and phosphorus(P) deficiency conditions, while the broomrape germination inducing activities of the rhizosphere soil were increased by 2 and 2.7 times. The biomass of WF declined by 77% and 69% at the P deficiency and potassium(K) excess conditions, while the germination inducing activities of the rhizosphere soils were increased by 47% and 20%. Furthermore,-N,-P and +K significantly increased the germination inducing ability of WF to seeds of O. cumana and P. aegytiace by seven times and two times comparing with control, whereas-N,-P and +K also increased the germination inducing ability of RG but not significantly. A significant negative correlation between the biomass of the seedlings and the germination inducing activities of the root exudates of tobacco seedlings was discovered(r =-0.785,p < 0.01), indicating nutrient stresses increased the germination inducing activities of tobacco seedlings.3. The allelopathic potential of the root exudates of rice cultivars to wheat, lettuce and itself were significantly different. Zhongzao 22, Zhongzu 14 and Zhunliangyou 527 had greater inhibitory effects on the germination and root growth of lettuce seeds. I-Kung-Pao, Ganxin 203, Zhongzu 14 and Zhunliangyou 527 had shown the higher autotoxicity effects. All the on-test rice cultivars showed strong inhibitory effects on wheat seeds. I-Kung-Pao, Yongyou 13 and Yongyou 15 were with greater germination inducing ability on O. cumana and O. minor. There were significant correlations between the germination inducing activity of the rice root exudates on c lover broomrape seeds and the allelopathy indexes of rice on wheat(r = 0.691) or itself(r = 0.722). However, lettuce and wheat seeds were not suitable receptors for identifying the allelopathic potentials of the on-test rice cultivars on weeds in comparison with the current acknowledge, whereas broomrape seeds had shown agreeable results.4. The biomass and nutrient uptakes were significantly different between the strigolactone sythesis mutant rice(d27) and the wild type(WT). The germination inducing activities of methanol extracts of root and shoot of WT were significantly higher than that of d27. The height of WT at the heading stage was higher than d27, whereas the tiller number and the productive tiller number of d27 were higher than WT. However, the biomass of WT was significantly higher than that of d27 during the heading and full- ripe stages, especially the dry weight of WT seeds were 4 times of d27. The uptakes of N, P and K of WT were significantly higher than that of d27 at the heading and full-ripe stages, and the N and P accumulation of WT at full- ripe stage showed obviously polar accumulation, that meant the N and P accumulation ratio of seed or root to shoot being increased. Moreover, there were significant negative correlations of the accumulations of nutrients between root and shoot for WT, but for d27, the correlations were positive or less negative than WT.5. The competitive abilities of WT and d27 to weeds were different. At the heading stage, the shoot biomass of WT declined by 46% under the inter-cultivation with barnyard grass B1 and B2, while d27 declined by 63%-75%. Under the inter-cultivation with weedy rice, the increase of root biomass of W T was significant higher than that of d27. At the full-ripe stage, the seed yields of WT were 3-10 times higher than d27 under barnyard grass inter-cultivations. Moreover, WT exhibited higher competitiveness than d27, especially in the inter-cultivations with B1 at the heading stage, the N and K competitive ratio of WT were 2 times of d27, and the N, P and K competitive ratio of WT were 2-3 times of d27 at full-ripe stage. Therefore, by influencing plant architecture and nutrients uptakes, strigolactones could affect the inter-specific competitions bwtween crop and weeds. |
