Allelopathic effect of potato on Orabanche aegyptiaca Pers. seed germination

Orobanche aegyptiaca is a national-class quarantine species in China which is seriously harmful to melons and other economic crops. In this study, four commercial potato varieties ("Xiabodi", "Qingshu 168", "Jizhangshu No.5" and "Kexin No.1") were planted at a pot experiment, and their rhizosphere soils and plant organs (roots, stems and leaves) sampled at different growth stages (seedling, blossoming and tuber forming stages). Allelopathy potential of extracts (methanol and distilled water) of the above samples was measured in terms of germination rates of O. aegyptiaca seeds treated. The potatoes varieties with O. aegyptiaca seed high germination rates were chosen to prevent and kill off O. aegyptiaca seeds on croplands. The results showed that potato stimulated O. aegyptiaca germination, and the allelopathy potential differed with potato variety. The germination rates of O. aegyptiaca seeds treated with extracts of potato rhizosphere soil increased with potato growth. This suggested that potato secreted O. aegyptiaca germination stimulants at certain period of growth which in turn reduced O. aegyptiaca seed bank in the soil. At seedling stage of potato, the germination rate of O. aegyptiaca seeds treated with 10-fold diluted methanol extracts from potato roots was higher than those from the shoot system. Seeds treated with "Xiabodi" showed the highest germination rate (48.5%). At blossoming stage of potato, the germination rate of O. aegyptiaca seeds treated with 10-fold diluted methanol extracts from stems was highest, followed by those treated with root extracts and leaf extracts. Seeds treated with "Jizhangshu No.5" had the highest germination rate (33.0%). At tuber forming stage of potato, the germination rate of O. aegyptiaca seeds treated with 10-fold diluted methanol extracts from shoot system was higher than those from roots. Also seeds treated with "Xiabodi" gave the highest germination rate (51.2%). While the germination rate of O. aegyptiaca seeds treated with root extracts declined with increasing growth of potato, those treated with aerial part extract increased. This suggested that of O. aegyptiaca germination stimulants in potatoes gradually moved from the root to shoot system. The germination rate of O. aegyptiaca seeds induced by methanol extracts was higher than that induced by water extracts. In other words, methanol extracts had better effects as germination stimulants. Although artificially synthesized analogues had facilitated the germination of parasitic plant seeds, government protocols had limited their field application and dissemination. Other methods for controlling O. aegyptiaca seeds (e.g., artificial weeding, herbicide application, hybridization and transgenic method) for broomrape resistant cultivars had some disadvantages. Using potato to control O. aegyptiaca was therefore a promising strategy that not only reduced and eradicated parasitic weed seed deposition in soils, but also significantly reduced host broomrape damages. Root methanol extracts of "Xiabodi" at seedling stage induced higher germination rate (48.5%) of O. aegyptiaca seeds than other potato varieties. The parts from the shoot system at tuber formation stage also induced the highest germination rate (51.2%) of O. aegyptiaca seeds. Thus among the four potato varieties, "Xiabodi" had the highest allelopathic potential on O. aegyptiaca. Since potato was reproducible from tuber and reasonable quantities were obtainable in a short time, crop rotation was an adoptable method in areas with serious O. aegyptiaca damages. Specifically, "Xiabodi" has been planted for 5~8 years with returning straw to soil to not only reduce O. aegyptiaca seed bank in the soil, but also minimize O. aegyptiaca damages.