Developmental, cytological and transcriptional analysis of colchicine-induced autotetraploid fruit derived from Actinidia chinensis cv. ‘Hongyang’

• The tetraploid ‘Hongyang’ kiwifruit displays a distinct increase in fruit size compared to the diploid. • The tetraploid exhibits enhanced tolerance to bacterial canker disease (Psa). • Cytological analysis reveals that the larger fruit size results from both increased cell number and enlarged cell size. • Putative candidate DEGs associated with fruit size enlargement were identified through comparative transcriptome analysis. • The tetraploid ‘Hongyang’ represents a valuable new genetic resource for improved kiwifruit breeding. ‘Hongyang’ is the most widely cultivated red-fleshed diploid kiwifruit variety ( Actinidia chinensis ) in China. However, due to its relatively small fruit size, growers typically rely on the application of plant hormones to increase fruit size and yield. Here we report on the development and gene expression changes of ‘Hongyang’ autotetraploid fruits resulting from colchicine-induced chromosome doubling. The tetraploid displays a distinct increase in fruit size and tolerance to the canker disease caused by Pseudomonas syringae pv. actinidiae compared to the diploid. In addition, we found that both tetraploid and diploid fruits are characterized with similar nutritional composition. Cytological analysis showed that progression in fruit size from diploid to tetraploid is resulted from a concurrent increase in both cell number and cell size. Transcriptome analysis reveals the gene expression profiles at different fruit developmental stages, as well as candidate differentially expressed genes (DEGs) putatively associated with fruit size change. This study provides new resources for kiwifruit cultivation and genetic improvement, and sheds light into understanding the cytological/physiological aspects involved in enlargement of polyploid organs.