Effects of fluridone and norflurazon on seed conditioning and germination of root parasitic weeds, Orobanche minor, Striga asiatica and S. hermonthlca

摘要

Among the parasitic angiosperms, witchweeds (Striga) and broomrapes (Orobanche) are the two most devastating weeds that parasitise cereals and leguminous crops, respectively. Seeds of these parasites require a period of conditioning in a moist warm environment for several days in the dark to have the potential to germinate. Seeds then germinate only when they are exposed to germination stimulants released from roots of host and some non-host plants. Fluridone (FL) and norflurazon (NF) inhibit carotenoid biosynthesis by blocking desaturation of phytoene and are reported to promote germination of seeds and prevent the induction of secondary dormancy in many plant species. In this study, the effects of FL and NF on conditioning and seed germination ofOrobanche minor Smith, Striga asiatica (L.) Kuntze and S. hermonthica (Del.) Benth. were tested. The parasite seeds were placed in a conditioning solution in the dark or light at an optimal or at a supra-optimal temperature for a total of seven days. After the conditioning period, the seeds were grown in the terminal treatment solution containing 10~(10) M strigol in the dark for four days. The germination rate was determined under a binocular microscope. The conditioning period required before these parasitic weeds would germinate after an exposure to a germination stimulant was shortened by application with FL and NF at an early stage of conditioning. The inhibitory effects caused by both light and supra-optimal temperature on seed germination were eliminated by FL and NL (Table 1). In addition, treatment with FL or NF after conditioning in water induced seed germination and haustorium formation of S. asiatica in a manner similar to the effect of natural germination stimulants and haustorium inducing factors, respectively. In conclusion, FL and NL were shown not only to effectively release the seed dormancy of the root parasitic weeds, but also to stimulate seed germination. Based on these results we suggest that soil application of FL or NL wouldpromote seed conditioning of root parasites and render them more susceptible to control measures. In this way, these compounds may enhance the activity of germination stimulants (synthetic or natural) to induce a more effective 'suicidal germination' ofroot parasites.