Studies On Seed Germination And Its Regulation Of Root Parasitic Weed Orobanche

Three widely distributed species of broomrapes (Orobanche ramosa L., O. minor Sm. and O. aegyptiaca Pers.) were used in the experiments. The effects of preconditioning temperature, water potential and conditioning periods on germination of root parasitic weed Orobanche seeds were studied, the change of ABA content in seed was determined, and the method of quantitative trait with orthogonal polynomials was applied to analyze Orobanche seed germination percentage by regression model. The experiments were also conducted to investigate the regulation of various plant growth regulators and new herbicide ZJ273 {Propyl 4 - [2 - [(4,6-dimethoxy -2 -pyrimidinyl) oxy]-benzyl amino]benzoate} on germination of Orobanche seeds, and the restoration of various plant growth regulators on germination of Orobanche seeds conditioned under suboptimal temperature (at 13 ℃) and under water stress (at -1 MPa and -2 MPa). Meanwhile, in vitro culture of Orobanche was also studied in the experiment. The results showed that the highest germination percentage could be observed after Orobanche seeds conditioned at 18℃ and OMPa for 7 days. The linear or quadratic regression between germination percentages of O. aegyptiaca, O. ramosa seeds and preconditioning temperature or water potential was obtained. Their regression parameters mostly reached the most significant level, and the effect of preconditioning temperature or water potential on germination percentage could be predicted. However, for O. minor, there was no linear or quadratic regression relationship between germination percentage and preconditioning temperature or water potential.The results also showed that Orobanche seeds gain the ability to respond to germination stimulants only after conditioning for one day. All three species of Orobanche seeds reached the most highest germination percentage after conditioning for 7 days, but the germination was decreased sharply in O. aegyptiaca and O. ramosa when seeds conditioned for 9 days, while O. minor seeds could still kept higher germination. ABA contents in Orobanche seeds decreased remarkably after conditioning for 2 days. Though there were some variation in ABA contents regarding to O. ramosa, O. aegyptiaca and O. minorseeds, ABA levels decreased gradually with prolonged the conditioning period. No clear difference in ABA levels was observed among various water potential treatments. With the increase of the conditioning period (7, 14, 21 and 28 days), the germination percentage of O. ramosa and O. aegyptiaca progressively decreased. When conditioned at -2 MPa the germination percentage was lower than at 0 MPa and -1 MPa, especially at 13 °C and 28 °C. O. minor seeds could retain relatively high germination if conditioned at 18 "C, 23 °C or 28 °C, even after significantly extended conditioning periods (up to 84 days).Exogenous GA3 (30-100 mg L'1), norflurazon and fluridone (10-100 mg L'1), and brassinolide (0.5-1.0 mg L"1) increased seed germination, while 0.01 mg L"1 uniconazole significantly reduced germination rates of all three Orobanche spp. The promotive effects of GA3 and norflurazon and the inhibitory effect of uniconazole were evident even when they were treated for 3 days. Germination of Orobanche seeds was much lower when the unconditioned seeds were directly exposed to GR24 at 10"6 M. This early GR24 induced inhibition was however alleviated or even eliminated by the inclusion of GA3 or norflurazon (10-50 mg L'1) in the conditioning medium. On the other hand, the inclusion of uniconazole aggravated the GR24 inhibition effect, particularly in the case of O. ramosa.Exogenous GA3 (10 mg L"1), brassinolide (1 mg L'1) and fluridone (10 mg L'1) significantly increased the broomrape seed response to the germination stimulant GR24 (10"6 M) even when seeds were first conditioned at a suboptimal temperature and under water stress. The highest germination was obtained when the combined treatments with fluridone and brassinolide, or with GA3 and brassinolide were applied together with the germination stimulant. This indicates that there were additive effects among various plant growth regulators in the regulation of germination response in Orobanche seeds. With the prolongation of conditioning periods under low temperature stress, the restoration capacities of seed germination by a single growth regulator decreased, but the combined treatments of growth regulators retained their positive effects in restoring seed germination.There were no response to artifical germination stimulant GR24 after Orobanche aegyptiaca seeds conditioned for 3 days with 1-50 mg L'1 ZJ273. However, the germination was improved obviously if fluridone was applied together with GR24, these treatments could retained effective in restoring the seed germination even after Orobanche aegyptiaca seeds conditioned for 7 days with 1-20 mg L"1 ZJ273. For the treatment with 50 mg L"1 ZJ273, fluridone injected together with GR24 could partly restore the seed germination. The restoration of fluridone was decreased sharply while fluridone was applied in the conditioning medium, ZJ273 could partly neutralized the promotive effect of fluridone while they wereapplied together in the conditioning medium. Germination of conditioned seeds was inhibited by ZJ273 injected together with GR24. With the increase of the concentration of ZJ273, the germiantion percentage was decreased. However, the germination was higher while seeds conditioned with fluridone than with GA3 or water (the control). There was no seed germinated while 50 mg L'1 ZJ273 was applied together with GR24.Neither the B5 nor MS media alone could support the development of calli, the most effective callus induction were observed in the media containing 0.5-1.0 mg L*1 IAA or the combination of 0.2 mg L"1 NAA with 5.0 mg L'1 kinetin. These protocols produced root protrusions that resembled attachment organs of Orobanche seedlings, and proved effective in parasitizing host roots. Direct contact with medium inhibited haustorium development and prevented infection. To overcome this problem, certain root portions were isolated from the medium by inserting thin glass plates underneath. Calli were then placed on the raised root portions and successfully infected the roots.