Comprehensive estimation of physiological indices related to chilling resistance of melon seedlings

【Objective】The present study aimed to explore the relationships between 10 physiological indi-ces and chilling-resistance of melon seedlings.【Methods】A total of 26 melon germplasms with differentchilling resistance were used as experimental materials to investigate the response of 10 physiological in-dices(relative conductivity,malondialdehyde content,chlorophyll content,soluble sugar content,solu-ble protein content,free proline content,root vigor,POD activity,SOD activity and CAT activity)to lowtemperature. Several methods such as comparison of basic statistics,grey relative analysis,correlationanalysis,and principal component analysis were applied to estimate the chilling resistance of these germ-plasms.【Results】The maximum difference of chilling injury indices was observed among the germplasmseedlings under 4 ℃ for 48 h,with significance at P<0.01. Under this condition,each of the physiologi-cal indices varied significantly among the germplasm. Six indices,i.e.,malondialdehyde content,freeproline content,soluble sugar content,soluble protein content,chlorophyll content,and relative conduc-tivity,were highly related to chilling resistance as they had high relational degrees and correlation coeffi-cients. Also,these indices contributed mostly to chilling resistance in principal component analysis.Based on the dada of the six indices,all the germplasm were grouped into different groups with differentchilling resistance.【Conclusion】The ten physiological indices could be reduced to six indices,i.e.,malondialdehyde content,free proline content,soluble sugar content,soluble protein content,chlorophyllcontent,and relative conductivity. Of these,free proline content,soluble sugar content,and soluble pro-tein content could preferentially act as the indices for estimating melon chilling resistance and be used infurther chilling-resistance breeding.