These crops have been cultivated for a long time and only few cultivated varieties have spreaded to great area. The genetic resources of these crops has become more and more limited.

这些作物经长期的人工栽培和少数基因型品种的大面积推广，使这些农作物遗传资源越来越狭窄，受病虫和非生物逆境的危害越来越严重。