Using allelopathy and trap crops to eliminate soil bank of broomrape seed

Allelopathy should satisfy the following four factors:1) donor plants release allelochemicals that affect recipient plants continuously and quantitatively; 2) allelochemicals are isolated and identified from donor plants and affect accompanying plants in natural ecosystems, whether indoors or in fields; 3) donor plants produce and release allelochemicals in sufficient concentrations under natural conditions to adjacent recipient plants; and 4) allelochemicals released to recipient plants with enough biological activity to affect plants physiological and biochemical processes, which effect must exclude competition, animal abuse, pathogenic infection and the physical environment. Broomrapes (Orobanche spp.) are root holoparasites belonging to the genus Orobanche that lack chlorophyll and depend entirely on hosts for nutrients. Although the world of broomrape includes some 100 species, sunflower broomrape (O. cumana) and Egyptian broomrape (O. aegyptiace) are the most common species and have the widest distribution in China. Sunflower broomrape is mainly distributed in the northern regions of Shaanxi, Hebei, Xinjiang, Shanxi, Inner Mongolia and also in Northeast China. Egyptian broomrape is mainly distributed in Xinjiang and causes heavy and direct damage to tomatoes and potatoes. Broomrape seeds are light (3-6 μg) and small, and each broomrape plant can produce a huge quantity of tiny dust-like seeds which can survive in the soil for as long as 15-20 years. Broomrape seeds have special germination requirements-seeds should be kept in a warm and moist environment for 1-2 weeks and then exposed to germination stimulants. Under natural conditions, the germination stimulants are from host or the non-host plant root exudates. Once attached to a root, the parasite taps water and assimilates nutrients from host vessels. Efficient and economic control of broomrape is extremely difficult because infestation occurs primarily underground. The most effective way is to decrease soil bank of broomrape seeds. Trap crops are non-host plants whose roots exude chemical stimulants required for broomrape seed germination, but do not allow the attachment and development of the parasitic weed. In the absence of hosts, the seeds would germinate and not survive as the necessary conditions for live attachment to the host plant are not available; a process commonly referred to as "suicidal germination". This paper introduced advanced researches on the use of allelopathy and trap crops (wheat, corn, cotton, soybean, etc.) to eliminate soil bank of broomrape seeds.