Abstract: The new lettuce cultivar‘Zhongsheng 4’was bred through self-cross selection using a natural variant of the lettuce germplasm resource named KNV000485. It was bred in only two years by using plant factory-based speed breeding method,which shortened the breeding cycle by two thirds compared with traditional techniques. This new cultivar belongs to the looseleaf lettuce type. The mature leaves are green,narrowly oval in shape,rounded at the tip,soft and of medium thickness. The bubbles on the surface are prominent and the waviness at the edges of the leaves is mild. The ascorbic acid content is 0.125 mg · g^-1,the fresh weight is 367.7 g,the average yield is 39 059.4 kg · hm^-2,and the hydroponic cultivation yield is 39 118.8 kg · hm^-2. It is suitable for open-field cultivation in autumn and winter in the Chengdu Plain and surrounding hilly areas,as well as for hydroponic cultivation in greenhouses and plant factories.

Key words: lettuce, hydroponic cultivation, speed breeding chamber, cultivar