In the u . s . at least landscape logistics make it rather unlikely that herbicide - tolerant or bt crops will spread their biotech genes to weeds . that ' s because the gm crops sown in this country have no close relatives in the regions where they grow 在美国，至少还有生物地理的屏障， bt作物不太可能将植入的基因传播给野草，因为美国的基改作物多半种在没有近亲的地区。
