Colchicine-induced polyploidization in the lily cultivar ‘LC-4–1’ provides insights into physiological resistance in postharvest bulbs against Botrytis cinerea infection

Lily grey mould caused by Botrytis cinerea threatens the postharvest lily industry. Polyploidization can improve resistance to grey mould, but the adaptive mechanism is limited, especially in the bulbs. The benefits of polyploidization with respect to the novel Lilium variety ‘LC-4–1’ are unknown. Here, polyploidy was induced in ‘LC-4–1’ cutting shoots using colchicine concentrations of 0%–0.2% for varying durations. The optimal treatment was 0.10% colchicine induction for 36 h, achieving a morphological mutation rate of 81.67%. Of the 45 variant lines obtained for flow cytometry analysis, 17.78% were tetraploids. Cellular observations confirmed A21 and B12 as autotetraploids (2 n = 4x=48). A21 and B12 displayed larger flower diameters, delayed flowering periods, thicker stems, greater bulb weight, wider leaves, and larger guard cells than ‘LC-4–1’, with pollen viability rates of 28.17% and 33.52%, respectively. Critically, grey mould resistance was greater in tetraploid scales than in diploid scales. After B. cinerea infection , superoxide dismutase activity peaked at 2 dpi and peroxidase and oxalate oxidase activities peaked at 6 dpi in A21 and B12, respectively, and they were significantly higher in tetraploids than in diploids. Compared to diploids, the soluble sugar content in tetraploids reached the maximum value at 6 dpi and was maintained at higher levels, and the contents of total phenolic acids and total flavonoids were 6 dpi and 10 dpi higher, respectively. ISSR marker analysis revealed genetic variations in two tetraploids with rates of 14.61% and 16.85%, respectively. These results provide a novel germplasm resources for lily quality improvement and theoretical basis for disease control in postharvest bulb storage.