Based on the conserved sequence of the chitinase of crucifers,about 1 kb DNA fragment and 5'-end fragment(150 bp)were am根据已知的几种十字花科植物几丁质酶基因保守序列设计特异性引物,以大白菜叶片基因组DNA为模板,通过PCR反应扩增出约1kb的DNA片段和几丁质酶基因5′端序列片段(150bp)。