Phenotypic and physiological traits of autotetraploid ‘UF SunLime’ finger lime hybrid plants

Polyploidy induction is a promising strategy for enhancing stress tolerance and physiological resilience in crop plants. In this study, we investigated the efficacy of oryzalin treatment in inducing autoploidy in the finger lime hybrid 'UF SunLime' and examined its implication for cold tolerance and physiological responses to stress. Murashige and Skoog (MS) medium supplemented with oryzalin (0, 4, 6, and 8 mg/L) was applied to germinated seeds or adventitious shoots for 3 or 6 days, and the optimal conditions for maximal tetraploid induction were determined. Ploidy analysis using flow cytometry confirmed the ploidy level of the generated seedlings and shoots. Oryzalin applied at 6 mg/L for 6 days was the most effective concentration at generating the highest percentage of autotetraploids (60%), followed by 6 mg/L for 3 days (40%). Phenotypic characterization revealed significant differences in leaf morphology and chlorophyll content between tetraploid and diploid plants. Moreover, tetraploid plants exhibited decreased water loss and electrolyte leakage during cold stress assessments compared to their diploid counterparts. Pigment content analysis indicated differential responses to cold stress, with tetraploid plants generally exhibiting greater total phenolic compound content. Differential expression of transcription factors related to cold stress were identified as contributing factors to the cold tolerance induced by tetraploidy. Overall, our findings highlight the successful induction of autoploidy in the 'UF SunLime' finger lime hybrid cultivar via oryzalin treatment and provide insights into the physiological responses and stress tolerance conferred by polyploidization in citrus plants.